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[[File:Cloud computing.svg|400px|thumb|Cloud computing logical diagram]]
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'''Cloud computing''' is the use of [[computing]] resources (hardware and software) which are available in a remote location and accessible over a [[Computer network|network]] (typically the [[Internet]]). The name comes from the common use of a cloud-shaped symbol as an abstraction for the complex infrastructure it contains in system diagrams. Cloud computing entrusts remote services with a user's data, software and computation.

End users access cloud-based [[application software|applications]] through a [[web browser]] or a light-weight desktop or [[mobile app]] while the [[business software]] and user's data are stored on servers at a remote location. Proponents claim that cloud computing allows companies to avoid upfront infrastructure costs, and focus on projects that differentiate their businesses instead of infrastructure.<ref name="aws.amazon">{{cite web|url=http://aws.amazon.com/what-is-cloud-computing/|title=What is Cloud Computing? |work=Amazon Web Services |date=2013-3-19 |accessdate=2013-3-20}}</ref> Proponents also claim that cloud computing allows enterprises to get their applications up and running faster, with improved manageability and less maintenance, and enables IT to more rapidly adjust resources to meet fluctuating and unpredictable business demand.<ref name="aws.amazon" /><ref>{{cite web|url=http://it.tmcnet.com/channels/cloud-storage/articles/211183-rising-cloud-storage-market-opportunity-strengthens-vendors.htm |title=Baburajan, Rajani, "The Rising Cloud Storage Market Opportunity Strengthens Vendors," infoTECH, August 24, 2011 |publisher=It.tmcnet.com |date=2011-08-24 |accessdate=2011-12-02}}</ref><ref>{{cite web|url=http://www.thectoforum.com/content/converged-infrastructure-0|author=Oestreich, Ken, |title=Converged Infrastructure |work=CTO Forum |publisher=Thectoforum.com |date=2010-11-15 |accessdate=2011-12-02}}</ref>

In the [[business model]] using software as a service (SaaS), users are provided access to application software and databases. Cloud providers manage the infrastructure and platforms that run the applications. SaaS is sometimes referred to as "on-demand software" and is usually priced on a pay-per-use basis. SaaS providers generally price applications using a subscription fee.

Proponents claim SaaS allows a business the potential to reduce IT operational costs by outsourcing hardware and software maintenance and support to the cloud provider. This enables the business to reallocate IT operations costs away from hardware/software spending and personnel expenses, towards meeting other goals. In addition, with applications hosted centrally, updates can be released without the need for users to install new software. One drawback of SaaS is that the users' data are stored on the cloud provider's server. As a result, there could be unauthorized access to the data.

Cloud computing relies on sharing of resources to achieve coherence and [[economies of scale]] similar to a [[utility computing|utility]] (like the [[Electrical grid|electricity grid]]) over a network.<ref name="nist">{{cite web|title=The NIST Definition of Cloud Computing |url=http://csrc.nist.gov/publications/nistpubs/800-145/SP800-145.pdf|publisher=National Institute of Standards and Technology|accessdate=24 July 2011}}</ref> At the foundation of cloud computing is the broader concept of [[converged infrastructure]] and [[shared services]].

==History==

The underlying concept of cloud computing dates back to the 1950s, when large-scale [[Mainframe computer|mainframe]] became available in academia and corporations, accessible via [[thin client]]s / [[computer terminal|terminal]] computers, often referred to as "dumb terminals", because they were used for communications but had no internal computational capacities. To make more efficient use of costly mainframes, a practice evolved that allowed multiple users to share both the physical access to the computer from multiple terminals as well as to share the [[CPU]] time. This eliminated periods of inactivity on the mainframe and allowed for a greater return on the investment. The practice of sharing CPU time on a mainframe became known in the industry as [[time-sharing]].<ref name="StracheyTSO">{{cite journal|last=Strachey|first=Christopher|title=Time Sharing in Large Fast Computers|journal=Proceedings of the International Conference on Information processing, UNESCO|year=1959|month=June|series=paper B.2.19|pages=336–341}}</ref>

In the 1990s, telecommunications companies, who previously offered primarily dedicated point-to-point data circuits, began offering [[virtual private network]] (VPN) services with comparable quality of service, but at a lower cost. By switching traffic as they saw fit to balance server use, they could use overall network bandwidth more effectively. They began to use the cloud symbol to denote the demarcation point between what the provider was responsible for and what users were responsible for. Cloud computing extends this boundary to cover servers as well as the network infrastructure.<ref>{{cite web|url=http://mirror.switch.ch/ftp/doc/ietf/ipatm/atm-minutes-93jul.txt | publisher = Switch | location = [[Switzerland|CH]] |title=July, 1993 meeting report from the IP over ATM working group of the IETF | accessdate=2010-08-22}}</ref>

As computers became more prevalent, scientists and technologists explored ways to make large-scale computing power available to more users through time sharing, experimenting with algorithms to provide the optimal use of the infrastructure, platform and applications with prioritized access to the CPU and efficiency for the end users.<ref name="MITCorbato">{{cite web|last=Corbató|first=Fernando J.|title=An Experimental Time-Sharing System|url=http://larch-www.lcs.mit.edu:8001/~corbato/sjcc62/|work=SJCC Proceedings|publisher=MIT|accessdate=3 July 2012}}</ref>

[[John McCarthy (computer scientist)|John McCarthy]] opined in the 1960s that "computation may someday be organized as a [[public utility]]." [http://www.technologyreview.com/news/425623/the-cloud-imperative/] Almost all the modern-day characteristics of cloud computing (elastic provision, provided as a utility, online, illusion of infinite supply), the comparison to the electricity industry and the use of public, private, government, and community forms, were thoroughly explored in [[Douglas Parkhill]]'s 1966 book, ''The Challenge of the Computer Utility''. Other scholars have shown that cloud computing's roots go all the way back to the 1950s when scientist [[Herb Grosch]] (the author of [[Grosch's law]]) postulated that the entire world would operate on dumb terminals powered by about 15 large data centers.<ref>{{Cite journal | url = http://ssrn.com/abstract=1941494 | title = Regulation of the Cloud in India | last = Ryan | last2 = Falvey | last3 = Merchant | journal = Journal of Internet Law | volume = 15 | month = October | year = 2011 | issue = 4 | postscript = <!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->{{inconsistent citations}}}}</ref> Due to the expense of these powerful computers, many corporations and other entities could avail themselves of computing capability through time sharing and several organizations, such as GE's GEISCO, IBM subsidiary The [[Service Bureau Corporation]] (SBC, founded in 1957), Tymshare (founded in 1966), National CSS (founded in 1967 and bought by Dun & Bradstreet in 1979), Dial Data (bought by Tymshare in 1968), and [[Bolt, Beranek and Newman]] (BBN) marketed time sharing as a commercial venture.

The development of the Internet from being document centric via semantic data towards more and more services was described as "Dynamic Web".<ref>Andreas Tolk. 2006. What Comes After the Semantic Web - PADS Implications for the Dynamic Web. 20th Workshop on Principles of Advanced and Distributed Simulation (PADS '06). IEEE Computer Society, Washington, DC, USA</ref> This contribution focused in particular in the need for better meta-data able to describe not only implementation details but also conceptual details of model-based applications.

The ubiquitous availability of high-capacity networks, low-cost computers and storage devices as well as the widespread adoption of [[hardware virtualization]], [[service-oriented architecture]], [[Autonomic Computing|autonomic]], and utility computing have led to a tremendous growth in cloud computing.<ref>{{Cite news|url= http://www.economist.com/displaystory.cfm?story_id=14637206|title= Cloud Computing: Clash of the clouds|date= 2009-10-15 | publisher = The Economist|accessdate=2009-11-03}}</ref><ref name="gartner">{{cite web|url=http://www.gartner.com/it/page.jsp?id=707508 |title= Gartner Says Cloud Computing Will Be As Influential As E-business |publisher=Gartner |accessdate=2010-08-22}}</ref><ref name="really">{{cite web|url =http://www.infoworld.com/d/cloud-computing/what-cloud-computing-really-means-031 |title=What cloud computing really means|last=Gruman|first= Galen|date = 2008-04-07 | work= [[InfoWorld]]| accessdate= 2009-06-02}}</ref>

After the [[dot-com bubble]], [[Amazon.com|Amazon]] played a key role in the development of cloud computing by modernizing their [[data center]]s, which, like most [[computer networks]], were using as little as 10% of their capacity at any one time, just to leave room for occasional spikes. Having found that the new cloud architecture resulted in significant internal efficiency improvements whereby small, fast-moving "two-pizza teams" (teams small enough to feed with two pizzas) could add new features faster and more easily, Amazon initiated a new product development effort to provide cloud computing to external customers, and launched [[Amazon Web Services|Amazon Web Service (AWS)]] on a utility computing basis in 2006.<ref name="amazon">{{Cite journal | url = http://www.businessweek.com/magazine/content/06_46/b4009001.htm | title = Jeff Bezos' Risky Bet | journal = Business Week | postscript = <!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->{{inconsistent citations}}}}</ref><ref name="AWS">{{Cite journal | date = 2010-06-17 | url =http://itknowledgeexchange.techtarget.com/cloud-computing/2010/06/17/amazons-early-efforts-at-cloud-computing-partly-accidental/ | publisher = Tech Target | title = IT Knowledge Exchange | contribution = Amazon's early efforts at cloud computing partly accidental | postscript = <!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->{{inconsistent citations}}}}</ref>

In early 2008, [[Eucalyptus (computing)|Eucalyptus]] became the first open-source, AWS API-compatible platform for deploying private clouds. In early 2008, [[OpenNebula]], enhanced in the RESERVOIR European Commission-funded project, became the first open-source software for deploying private and hybrid clouds, and for the federation of clouds.<ref>B Rochwerger, J Caceres, RS Montero, D Breitgand, E Elmroth, A Galis, E Levy, [[Ignacio M. Llorente|IM Llorente]], K Nagin, Y Wolfsthal, E Elmroth, J Caceres, M Ben-Yehuda, W Emmerich, F Galan. "The RESERVOIR Model and Architecture for Open Federated Cloud Computing", IBM Journal of Research and Development, Vol. 53, No. 4. (2009)</ref> In the same year, efforts were focused on providing [[quality of service]] guarantees (as required by real-time interactive applications) to cloud-based infrastructures, in the framework of the IRMOS European Commission-funded project, resulting to a '''real-time cloud environment'''.<ref>D Kyriazis, A Menychtas, G Kousiouris, K Oberle, T Voith, M Boniface, E Oliveros, T Cucinotta, S Berger, "A Real-time Service Oriented Infrastructure", International Conference on Real-Time and Embedded Systems (RTES 2010), Singapore, November 2010</ref> By mid-2008, Gartner saw an opportunity for cloud computing "to shape the relationship among consumers of IT services, those who use IT services and those who sell them"<ref>[http://www.networkworld.com/newsletters/itlead/2008/070708itlead1.html Keep an eye on cloud computing], Amy Schurr, Network World, 2008-07-08, citing the [[Gartner]] report, "Cloud Computing Confusion Leads to Opportunity". Retrieved 2009-09-11.</ref> and observed that "organizations are switching from company-owned hardware and software assets to per-use service-based models" so that the "projected shift to computing&nbsp;... will result in dramatic growth in IT products in some areas and significant reductions in other areas."<ref>[http://www.gartner.com/it/page.jsp?id=742913 Gartner Says Worldwide IT Spending On Pace to Surpass Trillion in 2008], Gartner, 2008-08-18. Retrieved 2009-09-11.</ref>

On March 1, 2011, IBM announced the [[IBM cloud computing#IBM_SmartCloud|IBM SmartCloud]] framework to support Smarter Planet.<ref>{{cite web|title=Launch of IBM Smarter Computing|url=https://www-304.ibm.com/connections/blogs/IBMSmarterSystems/date/201102?lang=en_us|accessdate=1 March 2011}}</ref> Among the various components of the Smarter Computing foundation, cloud computing is a critical piece.

==Similar systems and concepts==
<!-- this need not enumerate every different type of computing, just the top half-dozen that are provably linked to cloud computing -->

Cloud Computing is the result of evolution and adoption of existing technologies and paradigms. The goal of cloud computing is to allow users to take benefit from all of these technologies, without the need for deep knowledge about or expertise with each one of them. The cloud aims to cut costs, and help the users focus on their core business instead of being impeded by IT obstacles.<ref name=HAM2012>{{cite book|last=HAMDAQA|first=Mohammad|title=Cloud Computing Uncovered: A Research Landscape|year=2012|publisher=Elsevier Press|isbn=0-12-396535-7|pages=41–85|url=http://www.stargroup.uwaterloo.ca/~mhamdaqa/publications/Cloud_Computing_Uncovered.pdf}}</ref>

The main enabling technology for cloud computing is [[virtualization]]. Virtualization abstracts the physical infrastructure, which is the most rigid component, and makes it available as a soft component that is easy to use and manage. By doing so, virtualization provides the agility required to speed up IT operations, and reduces cost by increasing infrastructure [[utilization]]. On the other hand, autonomic computing automates the process through which the user can provision resources [[Code on demand|on-demand]]. By minimizing user involvement, automation speeds up the process and reduces the possibility of human errors.<ref name=HAM2012/>

Users face difficult business problems every day. Cloud computing adopts concepts from [[Service-oriented Architecture]] (SOA) that can help the user break these problems into [[Service (systems architecture)|services]] that can be integrated to provide a solution. Cloud computing provides all of its resources as services, and makes use of the well-established standards and best practices gained in the domain of SOA to allow global and easy access to cloud services in a standardized way.

Cloud computing also leverages concepts from [[utility computing]] in order to provide [[Performance metric|metric]]s for the services used. Such metrics are at the core of the public cloud pay-per-use models. In addition, measured services are an essential part of the feedback loop in autonomic computing, allowing services to scale on-demand and to perform automatic failure recovery.

Cloud computing is a kind of [[grid computing]]; it has evolved from grid computing by addressing the [[Quality of service|QoS]] (quality of service) and [[reliability (computer networking)|reliability]] problems. Cloud computing provides the tools and technologies to build data/compute intensive parallel applications with much more affordable prices compared to traditional [[parallel computing]] techniques.<ref name=HAM2012/>

Cloud computing shares characteristics with:
* [[Client–server model]] — ''Client–server computing'' refers broadly to any [[distributed application]] that distinguishes between service providers (servers) and service requesters (clients).<ref>{{cite web|url=http://java.sun.com/developer/Books/jdbc/ch07.pdf|publisher=Sun Microsystem|title=Distributed Application Architecture|accessdate=2009-06-16}}</ref>
* [[Grid computing]] — "A form of [[distributed computing|distributed]] and [[parallel computing]], whereby a 'super and virtual computer' is composed of a [[Cluster (computing)|cluster]] of networked, [[Loose coupling|loosely coupled]] computers acting in concert to perform very large tasks."
* [[Mainframe computer]] — Powerful computers used mainly by large organizations for critical applications, typically bulk data processing such as [[census]], industry and consumer statistics, police and secret intelligence services, [[enterprise resource planning]], and financial [[transaction processing]].<ref>{{cite web|url=http://itknowledgeexchange.techtarget.com/mainframe-blog/sun-cto-cloud-computing-is-like-the-mainframe/ |title=Sun CTO: Cloud computing is like the mainframe |publisher=Itknowledgeexchange.techtarget.com |date=2009-03-11 |accessdate=2010-08-22}}</ref>
* [[Utility computing]] — The "packaging of [[Computational resource|computing resources]], such as computation and storage, as a metered service similar to a traditional public utility, such as electricity."<ref name="It's you've">{{cite web|url=http://portal.acm.org/citation.cfm?id=1496091.1496100&coll=&dl=ACM&CFID=21518680&CFTOKEN=18800807|title=It's probable that you've misunderstood 'Cloud Computing' until now | publisher= TechPluto |accessdate=2010-09-14}}</ref><ref>{{cite web|last=Danielson |first=Krissi |url=http://www.ebizq.net/blogs/saasweek/2008/03/distinguishing_cloud_computing/ |title=Distinguishing Cloud Computing from Utility Computing |publisher=Ebizq.net |date=2008-03-26 |accessdate=2010-08-22}}</ref>
* [[Peer-to-peer]] means distributed architecture without the need for central coordination. Participants are both suppliers and consumers of resources (in contrast to the traditional client–server model).
* [[Cloud gaming]]—also known as on-demand gaming—is a way of delivering games to computers. Gaming data is stored in the provider's server, so that gaming is independent of client computers used to play the game.

==Characteristics==
<!-- Pros and Cons are discussed as 'key features' as each typically has both -->
<!-- Separate pros and cons lists are very confusing, with the same topics, e.g., security, listed in both -->
Cloud computing exhibits the following key characteristics:
* '''Agility''' improves with users' ability to re-provision technological infrastructure resources.
* '''[[Application programming interface]]''' (API) accessibility to software that enables machines to interact with cloud software in the same way that a traditional user interface (e.g., a computer desktop) facilitates interaction between humans and computers. Cloud computing systems typically use Representational State Transfer ([[representational state transfer|REST]])-based APIs.
* '''Cost''' is claimed to be reduced, and in a public cloud delivery model [[capital expenditure]] is converted to [[operational expenditure]].<ref>{{cite web|url=http://www.cloudave.com/link/recession-is-good-for-cloud-computing-microsoft-agrees |title=Recession Is Good For Cloud Computing – Microsoft Agrees |publisher=CloudAve |date= |accessdate=2010-08-22}}</ref> This is purported to lower [[barriers to entry]], as infrastructure is typically provided by a third-party and does not need to be purchased for one-time or infrequent intensive computing tasks. Pricing on a utility computing basis is fine-grained with usage-based options and fewer IT skills are required for implementation (in-house).<ref name="idc">{{cite web|url=http://blogs.idc.com/ie/?p=190 |title=Defining "Cloud Services" and "Cloud Computing" |publisher=IDC |date=2008-09-23 |accessdate=2010-08-22}}</ref> The e-FISCAL project's state of the art repository<ref>{{cite web|url=http://www.efiscal.eu/state-of-the-art |title=e-FISCAL project state of the art repository}}</ref> contains several articles looking into cost aspects in more detail, most of them concluding that costs savings depend on the type of activities supported and the type of infrastructure available in-house.
* '''[[Device independence|Device and location independence]]'''<ref name="yarmis">{{cite web|last=Farber |first=Dan |url=http://news.cnet.com/8301-13953_3-9977049-80.html |title=The new geek chic: Data centers |publisher=[[CNET News]] |date=2008-06-25 |accessdate=2010-08-22}}</ref> enable users to access systems using a web browser regardless of their location or what device they are using (e.g., PC, mobile phone). As infrastructure is off-site (typically provided by a third-party) and accessed via the Internet, users can connect from anywhere.<ref name="idc" />
* '''[[Virtualization]]''' technology allows servers and storage devices to be shared and utilization be increased. Applications can be easily migrated from one physical server to another.
* '''[[Multitenancy]]''' enables sharing of resources and costs across a large pool of users thus allowing for:
** '''Centralization''' of infrastructure in locations with lower costs (such as real estate, electricity, etc.)
** '''Peak-load capacity''' increases (users need not engineer for highest possible load-levels)
** '''Utilisation and efficiency''' improvements for systems that are often only 10–20% utilised.<ref name="amazon"/><ref>{{cite journal|last=He|first=Sijin|coauthors=L. Guo, Y. Guo, M. Ghanem, |title=Improving Resource Utilisation in the Cloud Environment Using Multivariate Probabilistic Models|url=http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6253553 |publisher=2012 2012 IEEE 5th International Conference on Cloud Computing (CLOUD) |doi=10.1109/CLOUD.2012.66|isbn=978-1-4673-2892-0|pages=574–581}}</ref>
* '''[[Reliability (computer networking)|Reliability]]''' is improved if multiple redundant sites are used, which makes well-designed cloud computing suitable for [[business continuity]] and [[disaster recovery]].<ref>{{cite web|last=King |first=Rachael |url=http://www.businessweek.com/technology/content/aug2008/tc2008083_619516.htm |title=Cloud Computing: Small Companies Take Flight |publisher=Businessweek |date=2008-08-04 |accessdate=2010-08-22}}</ref>
* '''Scalability and elasticity''' via dynamic ("on-demand") [[provisioning]] of resources on a fine-grained, self-service basis near real-time,<ref name="vmstartuptime2012">{{cite journal|last=Mao|first=Ming|coauthors=M. Humphrey|title=A Performance Study on the VM Startup Time in the Cloud|journal=Proceedings of 2012 IEEE 5th International Conference on Cloud Computing (Cloud2012)|year=2012|url=http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6253534&isnumber=6253471|doi=10.1109/CLOUD.2012.103|isbn=978-1-4673-2892-0|pages=423}}</ref><ref>{{cite journal|last=He|first=Sijin|coauthors=L. Guo, Y. Guo|title=Real Time Elastic Cloud Management for Limited Resources|journal=Proceedings of 2011 IEEE 4th International Conference on Cloud Computing (Cloud2011)|year=2011|url=http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6008763|doi=10.1109/CLOUD.2011.47|isbn=978-0-7695-4460-1|pages=622–629}}</ref> without users having to engineer for peak loads.<ref>{{cite web|title=Defining and Measuring Cloud Elasticity|url=http://digbib.ubka.uni-karlsruhe.de/volltexte/1000023476|publisher=KIT Software Quality Departement|accessdate=13 August 2011}}</ref><ref>{{cite web|title=Economies of Cloud Scale Infrastructure|url=http://www.youtube.com/watch?v=nfDsY3f4nVI|publisher=Cloud Slam 2011|accessdate=13 May 2011}}</ref><ref>{{cite journal|last=He|first=Sijin|coauthors=L. Guo, Y. Guo, C. Wu, M. Ghanem, R. Han|title=Elastic Application Container: A Lightweight Approach for Cloud Resource Provisioning|url=http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6184989 |publisher=2012 IEEE 26th International Conference on Advanced Information Networking and Applications (AINA) |doi=10.1109/AINA.2012.74|isbn=978-1-4673-0714-7|pages=15–22}}</ref>
* '''[[Computer performance|Performance]]''' is monitored, and consistent and loosely coupled architectures are constructed using [[web services]] as the system interface.<ref name="idc" />
* '''[[Computer security|Security]]''' could improve due to centralization of data, increased security-focused resources, etc., but concerns can persist about loss of control over certain sensitive data, and the lack of security for stored kernels.<ref>{{cite web|url=http://www.cryptoclarity.com/CryptoClarityLLC/Welcome/Entries/2009/7/23_Encrypted_Storage_and_Key_Management_for_the_cloud.html |title=Encrypted Storage and Key Management for the cloud |publisher=Cryptoclarity.com |date=2009-07-30 |accessdate=2010-08-22}}</ref> Security is often as good as or better than other traditional systems, in part because providers are able to devote resources to solving security issues that many customers cannot afford.<ref>{{cite web|last=Mills |first=Elinor |url=http://news.cnet.com/8301-1009_3-10150569-83.html |title=Cloud computing security forecast: Clear skies |publisher=CNET News |date=2009-01-27 |accessdate=2010-08-22}}</ref> However, the complexity of security is greatly increased when data is distributed over a wider area or greater number of devices and in multi-tenant systems that are being shared by unrelated users. In addition, user access to security [[audit log]]s may be difficult or impossible. Private cloud installations are in part motivated by users' desire to retain control over the infrastructure and avoid losing control of information security.
* ''' [[Software maintenance|Maintenance]]''' of cloud computing applications is easier, because they do not need to be installed on each user's computer and can be accessed from different places.

The National Institute of Standards and Technology's definition of cloud computing identifies "five essential characteristics":{{quote|text=''On-demand self-service.'' A consumer can unilaterally provision computing capabilities, such as server time and network storage, as needed automatically without requiring human interaction with each service provider.

''Broad network access.'' Capabilities are available over the network and accessed through standard mechanisms that promote use by heterogeneous thin or thick client platforms (e.g., mobile phones, tablets, laptops, and workstations).

''Resource pooling.'' The provider's computing resources are pooled to serve multiple consumers using a multi-tenant model, with different physical and virtual resources dynamically assigned and reassigned according to consumer demand.&nbsp;...

''Rapid elasticity.'' Capabilities can be elastically provisioned and released, in some cases automatically, to scale rapidly outward and inward commensurate with demand. To the consumer, the capabilities available for provisioning often appear unlimited and can be appropriated in any quantity at any time.

''Measured service.'' Cloud systems automatically control and optimize resource use by leveraging a metering capability at some level of abstraction appropriate to the type of service (e.g., storage, processing, bandwidth, and active user accounts). Resource usage can be monitored, controlled, and reported, providing transparency for both the provider and consumer of the utilized service.|sign=National Institute of Standards and Technology<ref name="nist"/>}}

===On-demand self-service===
{{See also|Provisioning#Self-service provisioning for cloud computing services|label 1=Self-service provisioning for cloud computing services|Service catalog#Service catalogs for cloud computing services|label 2=Service catalogs for cloud computing services}}
On-demand self-service allows users to obtain, configure and deploy cloud services themselves using cloud service catalogues, without requiring the assistance of IT.<ref>{{cite web|author=David Perera |url=http://www.fiercegovernmentit.com/story/real-obstacle-federal-cloud-computing/2012-07-12 |title=The real obstacle to federal cloud computing |publisher=FierceGovernmentIT |date=2012-07-12 |accessdate=2012-12-15}}</ref><ref>{{cite web|author=|url=http://cloudstory.in/2012/07/top-10-reasons-why-startups-should-consider-cloud/ |title=Top 10 Reasons why Startups should Consider Cloud |publisher=Cloudstory.in |date=2012-09-05 |accessdate=2012-12-15}}</ref> This feature is listed by the [[National Institute of Standards and Technology]] (NIST) as a characteristic of cloud computing.<ref name="nist" />

The self-service requirement of cloud computing prompts infrastructure vendors to create cloud computing templates, which are obtained from cloud service catalogues. Manufacturers of such templates or blueprints include [[BMC Software]] (BMC), with Service Blueprints as part of their cloud management platform<ref>{{cite web|url=http://www.eweek.com/reviews/bmc-service-catalog-enforces-workload-location |title=BMC Service Catalog Enforces Workload Location |publisher=eweek.com |date=2011-08-02 |accessdate=2013-03-10}}</ref> [[Hewlett-Packard]] (HP), which names its templates as HP Cloud Maps<ref>{{cite web|url=http://adtmag.com/blogs/watersworks/2010/08/hps-turn-key-private-cloud.aspx |title=HP's Turn-Key Private Cloud - Application Development Trends |publisher=Adtmag.com |date=2010-08-30 |accessdate=2012-12-15}}</ref> [[RightScale]]<ref name="Babcock">{{cite web|last=Babcock |first=Charles |url=http://www.informationweek.com/news/cloud-computing/infrastructure/229900165 |title=RightScale Launches App Store For Infrastructure - Cloud-computing |publisher=Informationweek.com |date=2011-06-03 |accessdate=2012-12-15}}</ref> and [[Red Hat]], which names its templates CloudForms.<ref name="Jackson">{{cite web|url=http://www.techworld.com.au/article/426861/red_hat_launches_hybrid_cloud_management_software |title=Red Hat launches hybrid cloud management software - Open Source |publisher=Techworld |date=2012-06-06 |accessdate=2012-12-15}}</ref>

The templates contain predefined configurations used by consumers to set up cloud services. The templates or blueprints provide the technical information necessary to build ready-to-use clouds.<ref name="Babcock" /> Each template includes specific configuration details for different cloud infrastructures, with information about servers for specific tasks such as hosting applications, databases, websites and so on.<ref name="Babcock" /> The templates also include predefined Web service, the operating system, the database, security configurations and load balancing.<ref name="Jackson" />

Cloud computing consumers use cloud templates to move applications between clouds through a self-service portal. The predefined blueprints define all that an application requires to run in different environments. For example, a template could define how the same application could be deployed in cloud platforms based on Amazon Web Service, VMware or Red Hat.<ref>{{cite web |last=Brown |first=Rodney |title=Spinning up the instant cloud |work=CloudEcosystem |date=April 10, 2012 |url=http://www.cloudecosystem.com/author.asp?section_id=1873&doc_id=242031}}</ref> The user organization benefits from cloud templates because the technical aspects of cloud configurations reside in the templates, letting users to deploy cloud services with a push of a button.<ref>{{cite web |url= http://searchcloudapplications.techtarget.com/news/2240111861/VIP-Art-Fair-picks-OpDemand-over-RightScale-for-IaaS-management |title=VIP Art Fair picks OpDemand over RightScale for IaaS management |first=Adam |last=Riglian |work=Search Cloud Applications |publisher=TechTarget |date=December 1, 2011 |accessdate=January 25, 2013}}</ref><ref>{{cite web |url=http://www.infoworld.com/t/hybrid-cloud/hp-advances-public-cloud-part-of-ambitious-hybrid-cloud-strategy-190524 |title=HP advances public cloud as part of ambitious hybrid cloud strategy |publisher=InfoWorld |author=Samson, Ted |date=April 10, 2012 |deadurl=no |accessdate=2012-12-14}}</ref> Cloud templates can also be used by developers to create a catalog of cloud services.<ref>{{cite web |url=http://www.siliconindia.com/shownews/HP_Cloud_Maps_can_Ease_Application_Automation-nid-103866-cid-7.html |title=HP Cloud Maps can ease application automation |last1= |first1= |last2= |first2= |date= |work=SiliconIndia |publisher= |accessdate=22 January 2013}}</ref>

==Service models==
Cloud computing providers offer their services according to several fundamental models:<ref name="nist" /><ref name="Buyya">
{{cite book
|title=Cloud Computing: Principles and Paradigms
|editor=R. Buyya, J. Broberg, A.Goscinski
|year=February 2011
|publisher=Wiley Press
|location=New York, USA
|isbn=978-0-470-88799-8
|url=http://media.johnwiley.com.au/product_data/excerpt/90/04708879/0470887990-180.pdf
|chapter = Introduction to Cloud Computing
|first1 = William
|last1 = Voorsluys
|first2 = James
|last2 = Broberg
|first3 = Rajkumar
|last3 = Buyya
|pages=1–44
}}
</ref> infrastructure as a service (IaaS), platform as a service (PaaS), and software as a service (SaaS) where IaaS is the most basic and each higher model abstracts from the details of the lower models. Other key components in XaaS are described in a comprehensive taxonomy model published in 2009,<ref>{{cite web|title=Tony Shan, "Cloud Taxonomy and Ontology" |url=http://cloudonomic.blogspot.com/2009/02/cloud-taxonomy-and-ontology.html |year=February 2009 |accessdate=2 February 2009}}</ref> such as Strategy-as-a-Service, Collaboration-as-a-Service, Business Process-as-a-Service, Database-as-a-Service, etc. In 2012, network as a service (NaaS) and communication as a service (CaaS) were officially included by ITU (International Telecommunication Union) as part of the basic cloud computing models, recognized service categories of a telecommunication-centric cloud ecosystem.<ref>{{cite web|title=ITU-T NEWSLOG - CLOUD COMPUTING AND STANDARDIZATION: TECHNICAL REPORTS PUBLISHED|url=http://www.itu.int/ITU-T/newslog/Cloud+Computing+And+Standardization+Technical+Reports+Published.aspx|publisher=International Telecommunication Union (ITU)|accessdate=16 December 2012}}</ref>
[[File:Cloud computing layers.png|right]]

===Infrastructure as a service (IaaS)===
{{See also|Category:Cloud infrastructure}}

In the most basic cloud-service model, providers of IaaS offer computers - physical or (more often) virtual machines - and other resources. (A [[hypervisor]], such as [[Xen]] or [[Kernel-based Virtual Machine|KVM]], runs the virtual machines as guests. Pools of hypervisors within the cloud operational support-system can support large numbers of virtual machines and the ability to scale services up and down according to customers' varying requirements.) IaaS clouds often offer additional resources such as a virtual-machine [[disk image]] library, raw (block) and file-based storage, firewalls, load balancers, IP addresses, [[VLAN|virtual local area networks]] (VLANs), and software bundles.<ref name="DHAC">
{{cite book
|title=Developing and Hosting Applications on the Cloud
|year=July 2012
|publisher=IBM Press
|isbn=978-0-13-306684-5
|url=http://www.ibmpressbooks.com/bookstore/product.asp?isbn=9780133066845
|chapter = Infrastructure as a Service Cloud Concepts
|first1 = Alex
|last1 = Amies
|first2 = Harm
|last2 = Sluiman
|first3 = Qiang Guo
|last3 = Tong
|first4 = Guo Ning
|last4 = Liu
}}
</ref>
IaaS-cloud providers supply these resources on-demand from their large pools installed in [[data centers]]. For [[Wide area network|wide-area]] connectivity, customers can use either the Internet or [[carrier cloud]]s (dedicated virtual private networks).

To deploy their applications, cloud users install operating-system images and their application software on the cloud infrastructure. In this model, the cloud user patches and maintains the operating systems and the application software. Cloud providers typically bill IaaS services on a utility computing basis{{citation needed|date=February 2013}}: cost reflects the amount of resources allocated and consumed.

Examples of IaaS providers include: [[Amazon EC2]], [[AirVM]], [[Azure Services Platform]], [[DynDNS]], [[Google Compute Engine]], [[HP Cloud Services|HP Cloud]], [[iland]], [[Joyent]], [[LeaseWeb]], [[Linode]], [[NaviSite]], [[Oracle Corporation|Oracle Infrastructure as a Service]], [[Rackspace]], [[ReadySpace Cloud Services]], [[Reliacloud|ReliaCloud]], [[SAVVIS]], [[SingleHop]], and [[Terremark]]

[[Cloud communications]] and [[cloud telephony]], rather than replacing local computing infrastructure, replace local telecommunications infrastructure with [[Voice over IP]] and other off-site Internet services.

===Platform as a service (PaaS)===
{{Main|Platform as a service}}
{{See also|Category:Cloud platforms}}

In the PaaS model, cloud providers deliver a [[computing platform]] typically including operating system, programming language execution environment, database, and web server. Application developers can develop and run their software solutions on a cloud platform without the cost and complexity of buying and managing the underlying hardware and software layers. With some PaaS offers, the underlying computer and storage resources scale automatically to match application demand such that cloud user does not have to allocate resources manually.

Examples of PaaS include: [[AWS Elastic Beanstalk]], [[Cloud Foundry]], [[Heroku]], [[Force.com]], [[Engine Yard|EngineYard]], [[Mendix]], [[OpenShift]], [[Google App Engine]], [[Azure Services Platform|Windows Azure Cloud Services]] and [[OrangeScape]].

===Software as a service (SaaS)===
{{Main|Software as a service}}

In the SaaS model, cloud providers install and operate application software in the cloud and cloud users access the software from cloud clients. Cloud users do not manage the cloud infrastructure and platform where the application runs. This eliminates the need to install and run the application on the cloud user's own computers, which simplifies maintenance and support. Cloud applications are different from other applications in their scalability—which can be achieved by cloning tasks onto multiple [[virtual machines]] at run-time to meet changing work demand.<ref name="hamdaqa">{{cite book
|title = A Reference Model for Developing Cloud Applications
|first = Mohammad
|last = Hamdaqa
|url = http://www.stargroup.uwaterloo.ca/~mhamdaqa/publications/A%20REFERENCEMODELFORDEVELOPINGCLOUD%20APPLICATIONS.pdf
}}</ref> [[Load balancer]]s distribute the work over the set of virtual machines. This process is transparent to the cloud user, who sees only a single access point. To accommodate a large number of cloud users, cloud applications can be ''[[multitenant]],'' that is, any machine serves more than one cloud user organization. It is common to refer to special types of cloud based application software with a similar naming convention: [[desktop as a service]], business process as a service, [[test environment as a service]], communication as a service.

The pricing model for SaaS applications is typically a monthly or yearly flat fee per user,<ref name="Chou">
{{cite book
|title = Introduction to Cloud Computing: Business & Technology
|first = Timothy
|last = Chou
|url = http://www.scribd.com/doc/64699897/Introduction-to-Cloud-Computing-Business-and-Technology
}}
</ref> so price is scalable and adjustable if users are added or removed at any point.<ref>{{cite web|title=HVD: the cloud's silver lining|url=http://www.intrinsictechnology.co.uk/FileUploads/HVD_Whitepaper.pdf|publisher=Intrinsic Technology|accessdate=30 August 2012}}</ref>

Examples of SaaS include: [[Google Apps]], [[Microsoft Office 365]], [[Onlive]], [[GT Nexus]], [[Marketo]], [[Casengo]] and [[TradeCard]].

===Network as a service (NaaS)===
{{Main|Network as a service}}

A category of cloud services where the capability provided to the cloud service user is to use network/transport connectivity services and/or inter-cloud network connectivity services.<ref name="ITU Focus Group">{{cite web|title=ITU Focus Group on Cloud Computing - Part 1|url=http://www.itu.int/en/ITU-T/focusgroups/cloud/Documents/FG-coud-technical-report.zip|publisher=International Telecommunication Union (ITU) TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU|accessdate=16 December 2012}}</ref> NaaS involves the optimization of resource allocations by considering network and computing resources as a unified whole.<ref>{{cite web|title=Cloud computing in Telecommunications|url=http://www.ericsson.com/res/thecompany/docs/publications/ericsson_review/2010/cloudcomputing.pdf|publisher=Ericsson|accessdate=16 December 2012}}</ref>

Traditional NaaS services include flexible and extended VPN, and bandwidth on demand.<ref name="ITU Focus Group" /> NaaS concept materialization also includes the provision of a virtual network service by the owners of the network infrastructure to a third party (VNP – VNO).<ref>{{cite web|title=Network Virtualisation – Opportunities and Challenges|url=http://archive.eurescom.eu/~pub/deliverables/documents/P1900-series/P1956/D1/P1956-D1.pdf|publisher=Eurescom|accessdate=16 December 2012}}</ref><ref>{{cite web|title=The role of virtualisation in future network architectures|url=http://www.change-project.eu/fileadmin/publications/Presentations/CHANGE_-_The_role_of_virtualisation_in_future_network_infrastructures_-_Warsaw_cluster_workshop_contribution.pdf|publisher=Change Project|accessdate=16 December 2012}}</ref>

==Cloud clients==
{{See also|Category:Cloud clients}}

Users access cloud computing using networked client devices, such as [[desktop computers]], [[laptop]]s, [[tablet computer|tablet]]s and [[smartphones]]. Some of these devices - ''cloud clients'' - rely on cloud computing for all or a majority of their applications so as to be essentially useless without it. Examples are [[thin clients]] and the browser-based [[Chromebook]]. Many cloud applications do not require specific software on the client and instead use a web browser to interact with the cloud application. With [[Ajax (programming)|Ajax]] and [[HTML5]] these [[Web user interface]]s can achieve a similar, or even better, [[look and feel]] to native applications. Some cloud applications, however, support specific client software dedicated to these applications (e.g., [[desktop virtualization|virtual desktop]] clients and most email clients). Some legacy applications (line of business applications that until now have been prevalent in [[thin client]] Windows computing) are delivered via a screen-sharing technology.

==Deployment models==
<!-- TODO: find source & add community cloud -->
[[File:Cloud computing types.svg|thumb|395px|right|Cloud computing types]]

===Public cloud===
{{mergefrom|Public cloud|date=February 2013}}
Public cloud applications, storage, and other resources are made available to the general public by a service provider. These services are free or offered on a pay-per-use model. Generally, public cloud service providers like Amazon AWS, Microsoft and Google own and operate the infrastructure and offer access only via Internet (direct connectivity is not offered).<ref name="idc"/>

===Community cloud===
[[Community cloud]] shares infrastructure between several organizations from a specific community with common concerns (security, compliance, jurisdiction, etc.), whether managed internally or by a third-party and hosted internally or externally. The costs are spread over fewer users than a public cloud (but more than a private cloud), so only some of the cost savings potential of cloud computing are realized.<ref name="nist" />

===Hybrid cloud===
Hybrid cloud is a composition of two or more clouds (private, community or public) that remain unique entities but are bound together, offering the benefits of multiple deployment models.<ref name="nist" />
Such composition expands deployment options for cloud services, allowing IT organizations to use public cloud computing resources to meet temporary needs.<ref>Metzler, Jim; Taylor, Steve. (2010-08-23) "Cloud computing: Reality vs. fiction," Network World. [http://www.networkworld.com/newsletters/frame/2010/082310wan1.html]</ref> This capability enables hybrid clouds to employ cloud bursting for scaling across clouds.<ref name="nist" />

Cloud bursting is an application deployment model in which an application runs in a private cloud or data center and "bursts" to a public cloud when the demand for computing capacity increases. A primary advantage of cloud bursting and a hybrid cloud model is that an organization only pays for extra compute resources when they are needed.<ref>Rouse, Margaret. "Definition: Cloudbursting," May 2011. SearchCloudComputing.com. [http://searchcloudcomputing.techtarget.com/definition/cloud-bursting]</ref>

Cloud bursting enables data centers to create an in-house IT infrastructure that supports average workloads, and use cloud resources from public or private clouds, during spikes in processing demands.<ref>Vizard, Michael. "How Cloudbursting 'Rightsizes' the Data Center", (2012-06-21). Slashdot. [http://slashdot.org/topic/datacenter/how-cloudbursting-rightsizes-the-data-center/]</ref>

By utilizing "hybrid cloud" architecture, companies and individuals are able to obtain degrees of fault tolerance combined with locally immediate usability without dependency on internet connectivity. Hybrid cloud architecture requires both on-premises resources and off-site (remote) server-based cloud infrastructure.

Hybrid clouds lack the flexibility, security and certainty of in-house applications.<ref>{{cite web | url=http://www.theregister.co.uk/2011/06/29/hybrid_cloud/ | title=When hybrid clouds are a mixed blessing | publisher=[http://www.theregister.co.uk ''The Register''] | date=June 29, 2011 | accessdate=March 28, 2012 | author=Stevens, Alan}}</ref> Hybrid cloud provides the flexibility of in house applications with the fault tolerance and scalability of cloud based services.

===Private cloud===
Private cloud is cloud infrastructure operated solely for a single organization, whether managed internally or by a third-party and hosted internally or externally.<ref name="nist" /> Undertaking a private cloud project requires a significant level and degree of engagement to virtualize the business environment, and requires the organization to reevaluate decisions about existing resources. When done right, it can improve business, but every step in the project raises security issues that must be addressed to prevent serious vulnerabilities.<ref>{{cite web|url= http://www.dell.com/Learn/us/en/rc956904/large-business/private-cloud-more-secure|title= Is a Private Cloud Really More Secure?|publisher=Dell.com | accessdate=07-11-12}} {{dead link|date=December 2012}}</ref>

They have attracted criticism because users "still have to buy, build, and manage them" and thus do not benefit from less hands-on management,<ref name="iwpc">{{cite web|last=Foley |first=John |url=http://www.informationweek.com/news/services/business/showArticle.jhtml?articleID=209904474 |title=Private Clouds Take Shape |publisher=InformationWeek |date= |accessdate=2010-08-22}}
</ref>
essentially "[lacking] the economic model that makes cloud computing such an intriguing concept".<ref>
{{cite web|last=Haff |first=Gordon |url=http://news.cnet.com/8301-13556_3-10150841-61.html |title=Just don't call them private clouds |publisher=CNET News |date=2009-01-27 |accessdate=2010-08-22}}</ref><ref>{{cite web|url=http://www.informationweek.com/cloud-computing/theres-no-such-thing-as-a-private-cloud/229207922 |title=There's No Such Thing As A Private Cloud |publisher=InformationWeek |date=2010-06-30 |accessdate=2010-08-22}}</ref>

{| class="wikitable"
|+ Comparison for SaaS
|-
! !! Public cloud !! Private cloud
|-
! scope="row" | Initial cost
| Typically zero || Typically high
|-
! scope="row" | Running cost
| Predictable || Unpredictable
|-
! scope="row" | Customization
| Impossible || Possible
|-
! scope="row" | Privacy
| No (Host has access to the data) || Yes
|-
! scope="row" | Single sign-on
| Impossible || Possible
|-
! scope="row" | Scaling up
| Easy while within defined limits || Laborious but no limits
|}

==Architecture==
[[File:CloudComputingSampleArchitecture.svg|thumb|325px|right|Cloud computing sample architecture]]

''Cloud architecture'',<ref>{{cite web|url=http://developer.amazonwebservices.com/connect/entry.jspa?externalID=1632&categoryID=100 |title=Building GrepTheWeb in the Cloud, Part 1: Cloud Architectures |publisher=Developer.amazonwebservices.com |date= |accessdate=2010-08-22}}</ref> the [[systems architecture]] of the [[software systems]] involved in the delivery of cloud computing, typically involves multiple ''cloud components'' communicating with each other over a loose coupling mechanism such as a messaging queue. Elastic provision implies intelligence in the use of tight or loose coupling as applied to mechanisms such as these and others.

===The Intercloud===
{{Main|Intercloud}}
The Intercloud<ref>{{Cite journal|date=2009-05-24|title= Blueprint for the Intercloud – Protocols and Formats for Cloud Computing Interoperability|publisher=IEEE Computer Society|pages=328–336|url=http://www2.computer.org/portal/web/csdl/doi/10.1109/ICIW.2009.55|doi=10.1109/ICIW.2009.55|last1=Bernstein|first1=David|last2=Ludvigson|first2=Erik|last3=Sankar|first3=Krishna|last4=Diamond|first4=Steve|last5=Morrow|first5=Monique|chapter=Blueprint for the Intercloud - Protocols and Formats for Cloud Computing Interoperability|isbn=978-1-4244-3851-8}}</ref> is an interconnected global "cloud of clouds"<ref name="kk">{{cite web|url=http://www.kk.org/thetechnium/archives/2007/11/a_cloudbook_for.php |title=Kevin Kelly: A Cloudbook for the Cloud |publisher=Kk.org |date= |accessdate=2010-08-22}}</ref><ref>{{cite web|url=http://samj.net/2009/06/intercloud-is-global-cloud-of-clouds.html |title=Intercloud is a global cloud of clouds |publisher=Samj.net |date=2009-06-22 |accessdate=2010-08-22}}</ref> and an extension of the Internet "network of networks" on which it is based.<ref>{{cite web|url=http://www.readwriteweb.com/archives/vint_cerf_despite_its_age_the.php?mtcCampaign=2765 |title=Vint Cerf: Despite Its Age, The Internet is Still Filled with Problems |publisher=Readwriteweb.com |date= |accessdate=2010-08-22}}</ref><ref>{{cite web|url=http://blogs.cisco.com/sp/comments/from_india_to_intercloud/ |title=SP360: Service Provider: From India to Intercloud |publisher=Blogs.cisco.com |date= |accessdate=2010-08-22}}</ref><ref>{{Cite news|author=Canada |url=http://www.theglobeandmail.com/servlet/story/LAC.20071129.TWLINKS29/TPStory/Business |title=Head in the clouds? Welcome to the future |publisher=Theglobeandmail.com |date= 2007-11-29|accessdate=2010-08-22 |location=Toronto}}</ref>

===Cloud engineering===
'''Cloud engineering''' is the application of [[engineering]] disciplines to cloud computing. It brings a systematic approach to the high-level concerns of commercialisation, standardisation, and governance in conceiving, developing, operating and maintaining cloud computing systems. It is a multidisciplinary method encompassing contributions from diverse areas such as [[systems engineering|systems]], [[software engineering|software]], [[web engineering|web]], [[performance engineering|performance]], [[information engineering|information]], [[security engineering|security]], [[platform engineering|platform]], [[Risk analysis (engineering)|risk]], and [[Quality control|quality]] engineering.

==Issues==

===Threats and opportunities of the cloud===
56% of European decision-makers estimate that the cloud is a priority between 2013 and 2014.<ref>{{cite book|title=Challenges & Opportunities for IT partners when transforming or creating a business in the Cloud|year=2012|publisher=compuBase consulting|page=16|page=77}}</ref> The cloud budget should reach 30% of the overall IT budget.{{citation needed|date=April 2013}}
But several deterrents to the cloud remain. Among them, are: reliability, availability of services and data, security, complexity, costs, regulations and legal issues, performance, migration, reversion, the lack of standards, and limited customization. The cloud also offers several strong points, however: infrastructure flexibility, faster deployment of applications and data, cost control, adaptation of cloud resources to real needs, improved productivity, etc.
The early 2010s cloud market is dominated by software and services in SaaS mode and IaaS (infrastructure), especially the private cloud. PaaS and the public cloud are further back.

===Privacy===
Privacy advocates have criticized the cloud model for hosting companies' greater ease can control—and thus, can monitor at will—communication between host company and end user, and access user data (with or without permission). Instances such as the [[Room 641A|secret NSA program]], working with [[AT&T]], and [[Verizon]], which recorded over 10 million telephone calls between American citizens, causes uncertainty among privacy advocates, and the greater powers it gives to telecommunication companies to monitor user activity.<ref>{{Cite news|last=Cauley |first=Leslie |url=http://www.usatoday.com/news/washington/2006-05-10-nsa_x.htm |title=NSA has massive database of Americans' phone calls |publisher=USATODAY.com |date=2006-05-11 |accessdate=2010-08-22}}</ref> A cloud service provider (CSP) can complicate data privacy because of the extent of virtualization (virtual machines) and [[cloud storage]] used to implement cloud service.<ref name="Securing The Cloud Winkler">{{cite book|last= Winkler |first= Vic |title= Securing the Cloud: Cloud Computer Security Techniques and Tactics |year= 2011 |publisher= Elsevier |location= [[Waltham, Massachusetts]] |isbn= 978-1-59749-592-9 |page= 60 |url= http://www.elsevier.com/wps/find/bookdescription.cws_home/723529/description }}</ref> CSP operations, customer or tenant data may not remain on the same system, or in the same data center or even within the same provider's cloud; this can lead to legal concerns over jurisdiction. While there have been efforts (such as [[US-EU Safe Harbor]]) to "harmonise" the legal environment, providers such as Amazon still cater to major markets (typically the United States and the [[European Union]]) by deploying local infrastructure and allowing customers to select "availability zones."<ref>{{cite web|url= http://developer.amazonwebservices.com/connect/entry.jspa?externalID=1347&categoryID=112 |title= Feature Guide: Amazon EC2 Availability Zones |publisher= Amazon Web Services |date= |accessdate= 2010-08-22 }}</ref>
Cloud computing poses privacy concerns because the service provider may access the data that is on the cloud at any point in time. They could accidentally or deliberately alter or even delete information.<ref>{{cite web|url= http://cacm.acm.org/magazines/2011/1/103200-cloud-computing-privacy-concerns-on-our-doorstep/fulltext |title= Cloud Computing Privacy Concerns on Our Doorstep }}</ref>

Postage and delivery services company [[Pitney Bowes]] launched Volly, a cloud-based, digital mailbox service to leverage its communication management assets. They also faced the technical challenge of providing strong data security and privacy. However, they were able to address the same concern by applying customized, application-level security, including encryption.<ref>{{cite web|url= http://smartenterpriseexchange.com/community/execution/blog/2011/06/13/cloud-enables-new-business-opportunity/fulltext |title= Cloud Enables New Business Opportunity }}</ref>

===Compliance===
To comply with regulations including [[FISMA]], [[HIPAA]], and [[Sarbox|SOX]] in the United States, the [[Data Protection Directive]] in the EU and the credit card industry's [[Payment Card Industry Data Security Standard|PCI DSS]], users may have to adopt ''community'' or ''hybrid'' deployment modes that are typically more expensive and may offer restricted benefits. This is how [[Google]] is able to "manage and meet additional government policy requirements beyond FISMA"<ref>{{cite web|url=http://searchcompliance.techtarget.com/news/article/0,289142,sid195_gci1377298,00.html |title=FISMA compliance for federal cloud computing on the horizon in 2010 |publisher=SearchCompliance.com |date= |accessdate=2010-08-22}}</ref><ref>{{cite web|url=http://googleenterprise.blogspot.com/2009/09/google-apps-and-government.html |title=Google Apps and Government |publisher=Official Google Enterprise Blog |date=2009-09-15 |accessdate=2010-08-22}}</ref> and Rackspace Cloud or QubeSpace are able to claim PCI compliance.<ref>{{cite web|url=http://www.rackspace.com/cloud/blog/2009/03/05/cloud-hosting-is-secure-for-take-off-mosso-enables-the-spreadsheet-store-an-online-merchant-to-become-pci-compliant/ |title=Cloud Hosting is Secure for Take-off: Mosso Enables The Spreadsheet Store, an Online Merchant, to become PCI Compliant |publisher=Rackspace |date=2009-03-14 |accessdate=2010-08-22}}</ref>

Many providers also obtain a [[Statement on Auditing Standards No. 70: Service Organizations|SAS 70 Type II]] audit, but this has been criticised on the grounds that the hand-picked set of goals and standards determined by the auditor and the auditee are often not disclosed and can vary widely.<ref>{{cite web|url=http://searchcloudcomputing.techtarget.com/news/article/0,289142,sid201_gci1374629,00.html |title=Amazon gets SAS 70 Type II audit stamp, but analysts not satisfied |publisher=SearchCloudComputing.com |date=2009-11-17 |accessdate=2010-08-22}}</ref> Providers typically make this information available on request, under [[non-disclosure agreement]].<ref>{{cite web|url=http://wistechnology.com/articles/6954/ |title=Assessing Cloud Computing Agreements and Controls |publisher=WTN News |date= |accessdate=2010-08-22}}</ref><ref>{{cite web|url=http://www.youtube.com/watch?v=wYiFdnZAlNQ |title=Cloud Certification From Compliance Mandate to Competitive Differentiator |publisher=Cloudcor |date= |accessdate=2011-09-20}}</ref>

Customers in the EU contracting with cloud providers outside the EU/EEA have to adhere to the EU regulations on export of personal data.<ref>{{cite web|url=http://www.thomashelbing.com/en/how-new-eu-rules-data-export-affect-companies-and-outside-eu |title=How the New EU Rules on Data Export Affect Companies in and Outside the EU &#124; Dr. Thomas Helbing – Kanzlei für Datenschutz-, Online- und IT-Recht |publisher=Dr. Thomas Helbing |date= |accessdate=2010-08-22}}</ref>

U.S. Federal Agencies have been directed by the Office of Management and Budget to use a process called FedRAMP (Federal Risk and Authorization Management Program) to assess and authorize cloud products and services. Federal CIO Steven VanRoekel issued a memorandum to federal agency Chief Information Officers on December 8, 2011 defining how federal agencies should use FedRAMP. FedRAMP consists of a subset of NIST Special Publication 800-53 security controls specifically selected to provide protection in cloud environments. A subset has been defined for the FIPS 199 low categorization and the FIPS 199 moderate categorization. The FedRAMP program has also established a Joint Accreditation Board (JAB) consisting of Chief Information Officers from DoD, DHS and GSA. The JAB is responsible for establishing accreditation standards for 3rd party organizations who perform the assessments of cloud solutions. The JAB also reviews authorization packages, and may grant provisional authorization (to operate). The federal agency consuming the service still has final responsibility for final authority to operate.<ref>{{cite web|url=http://www.gsa.gov/portal/category/102371|title=FedRAMP|date=2012-06-13|work=U.S. General Services Administration|accessdate=2012-06-17}}</ref>

A multitude of laws and regulations have forced specific compliance requirements onto many companies that collect, generate or store data. These policies may dictate a wide array of data storage policies, such as how long information must be retained, the process used for deleting data, and even certain recovery plans. Below are some examples of compliance laws or regulations.
*In the United States, the Health Insurance Portability and Accountability Act (HIPAA) requires a contingency plan that includes, data backups, data recovery, and data access during emergencies.
*The privacy laws of the Switzerland demand that private data, including emails, be physically stored in the Switzerland.
*In the United Kingdom, the Civil Contingencies Act of 2004 sets forth guidance for a Business contingency plan that includes policies for data storage.
In a virtualized cloud computing environment, customers may never know exactly where their data is stored. In fact, data may be stored across multiple data centers in an effort to improve reliability, increase performance, and provide redundancies. This geographic dispersion may make it more difficult to ascertain legal jurisdiction if disputes arise.<ref name="rtwadc01">{{cite web |url=http://rebustechnologies.com/wp-content/uploads/2011/12/WindowsAzure.pdf |title=Windows Azure: Using Windows Azure’s Service Bus to Solve Data Security Issues] |first1=Don|last1=Chambers |work=Rebus Technologies |date=July 2010 |deadurl=no |accessdate=2012-12-14}}</ref>

===Legal===
As with other changes in the landscape of computing, certain legal issues arise with cloud computing, including trademark infringement, security concerns and sharing of proprietary data resources.

The [[Electronic Frontier Foundation]] has criticized the [[United States government]] for considering during the [[Megaupload]] seizure process that people lose [[property right]]s by storing data on a cloud computing service.<ref>{{cite web |url=https://www.eff.org/deeplinks/2012/10/governments-attack-cloud-computing |title=Megaupload and the Government's Attack on Cloud Computing] |first1=Cindy |last1=Cohn |first2=Julie |last2=Samuels |work=Electronic Frontier Foundation |date=31 October 2012 |deadurl=no |accessdate=2012-12-14}}</ref>

One important but not often mentioned problem with cloud computing is the problem of who is in "possession" of the data. If a cloud company is the possessor of the data, the possessor has certain legal rights. If the cloud company is the "custodian" of the data, then a different set of rights would apply. The next problem in the legalities of cloud computing is the problem of legal ownership of the data. Many Terms of Service agreements are silent on the question of ownership.<ref>{{cite news |url=http://articles.latimes.com/2012/apr/26/business/la-fi-tech-savvy-cloud-services-20120426 |title=Who owns your stuff in the cloud? |date=26 April 2012 |first=Michelle |last=Maltais |newspaper=Los Angeles Times |deadurl=no |accessdate=2012-12-14}}</ref>

These legal issues are not confined to the time period in which the cloud based application is actively being used. There must also be consideration for what happens when the provider-customer relationship ends. In most cases, this event will be addressed before an application is deployed to the cloud. However, in the case of provider insolvencies or bankruptcy the state of the data may become blurred.<ref name="rtwadc01" />

===Vendor lock-in===
Because cloud computing is still relatively new, standards are still being developed.<ref name="joe">McKendrick, Joe. (2011-11-20) "Cloud Computing's Vendor Lock-In Problem: Why the Industry is Taking a Step Backward," Forbes.com [http://www.forbes.com/sites/joemckendrick/2011/11/20/cloud-computings-vendor-lock-in-problem-why-the-industry-is-taking-a-step-backwards/]</ref> Many cloud platforms and services are proprietary, meaning that they are built on the specific standards, tools and protocols developed by a particular vendor for its particular cloud offering.<ref name="joe" /> This can make migrating off a proprietary cloud platform prohibitively complicated and expensive.<ref name="joe" />

Three types of vendor lock-in can occur with cloud computing:<ref>Hinkle, Mark. (2010-6-9) "Three cloud lock-in considerations", Zenoss Blog [http://community.zenoss.org/blogs/zenossblog/2010/06/09/three-cloud-lock-in-considerations]</ref>

* Platform lock-in: cloud services tend to be built on one of several possible virtualization platforms, for example VMWare or Xen. Migrating from a cloud provider using one platform to a cloud provider using a different platform could be very complicated.
* Data lock-in: since the cloud is still new, standards of ownership, i.e. who actually owns the data once it lives on a cloud platform, are not yet developed, which could make it complicated if cloud computing users ever decide to move data off of a cloud vendor's platform.
* Tools lock-in: if tools built to manage a cloud environment are not compatible with different kinds of both virtual and physical infrastructure, those tools will only be able to manage data or apps that live in the vendor's particular cloud environment.

Heterogeneous cloud computing is described as a type of cloud environment that prevents vendor lock-in, and aligns with enterprise data centers that are operating hybrid cloud models.<ref>Staten, James (2012-07-23). "Gelsinger brings the 'H' word to VMware". ZDNet. [http://www.zdnet.com/gelsinger-brings-the-h-word-to-vmware-7000001416/]</ref> The absence of vendor lock-in lets cloud administrators select his or her choice of hypervisors for specific tasks, or to deploy virtualized infrastructures to other enterprises without the need to consider the flavor of hypervisor in the other enterprise.<ref>Vada, Eirik T. (2012-06-11) "Creating Flexible Heterogeneous Cloud Environments", page 5, Network and System Administration, Oslo University College [https://www.duo.uio.no/bitstream/handle/123456789/34153/thesis.pdf?sequence=1]</ref>

A heterogeneous cloud is considered one that includes on-premise private clouds, public clouds and software-as-a-service clouds. Heterogeneous clouds can work with environments that are not virtualized, such as traditional data centers.<ref>Geada, Dave. (June 2, 2011) "The case for the heterogeneous cloud," Cloud Computing Journal [http://cloudcomputing.sys-con.com/node/1841850]</ref> Heterogeneous clouds also allow for the use of piece parts, such as hypervisors, servers, and storage, from multiple vendors.<ref>Burns, Paul (2012-01-02). "Cloud Computing in 2012: What's Already Happening". Neovise.[http://www.neovise.com/cloud-computing-in-2012-what-is-already-happening]</ref>

Cloud piece parts, such as cloud storage systems, offer APIs but they are often incompatible with each other.<ref name= "Livenson">Livenson, Ilja. Laure, Erwin. (2011) "Towards transparent integration of heterogeneous cloud storage platforms", pages&nbsp;27–34, KTH Royal Institute of Technology, Stockholm, Sweden. [http://dl.acm.org/citation.cfm?id=1996020]</ref> The result is complicated migration between backends, and makes it difficult to integrate data spread across various locations.<ref name="Livenson" /> This has been described as a problem of vendor lock-in.<ref name="Livenson" />
The solution to this is for clouds to adopt common standards.<ref name="Livenson" />

Heterogeneous cloud computing differs from homogeneous clouds, which have been described as those using consistent building blocks supplied by a single vendor.<ref name="gannes">Gannes, Liz. GigaOm, "Structure 2010: Intel vs. the Homogeneous Cloud," June 24, 2010. [http://gigaom.com/2010/06/24/structure-2010-intel-vs-the-homogeneous-cloud/]</ref> Intel General Manager of high-density computing, Jason Waxman, is quoted as saying that a homogenous system of 15,000 servers would cost $6 million more in capital expenditure and use 1 megawatt of power.<ref name="gannes" />

===Open source===
{{See also|Category:Free software for cloud computing}}

[[Open-source software]] has provided the foundation for many cloud computing implementations, prominent examples being the [[Apache Hadoop|Hadoop framework]]<ref>{{cite web |url=http://www.networkworld.com/news/2008/072808-open-source-cloud-computing.html |title=Open source fuels growth of cloud computing, software-as-a-service |publisher=Network World |date=July 28, 2008 |author=Jon Brodkin |deadurl=no |accessdate=2012-12-14}}</ref> and [[VMware]]'s [[Cloud Foundry]].<ref>{{cite web |url=http://www.cmswire.com/cms/information-management/vmware-launches-open-source-paas-cloud-foundry-010941.php |title=VMware Launches Open Source PaaS Cloud Foundry |publisher=Simpler Media Group, Inc. |date=2011-04-21 |deadurl=no |accessdate=2012-12-14}}</ref> In November 2007, the [[Free Software Foundation]] released the [[Affero General Public License]], a version of [[GNU General Public License|GPLv3]] intended to close a perceived [[Legal technicality|legal loophole]] associated with [[free software]] designed to run over a network.<ref>{{cite web|url=http://redmonk.com/sogrady/2009/04/15/open-source-licensing-in-a-networked-age/ |title=AGPL: Open Source Licensing in a Networked Age |publisher=Redmonk.com |date=2009-04-15 |accessdate=2010-08-22}}</ref>

===Open standards===
{{See also|Category:Cloud standards}}
Most cloud providers expose APIs that are typically well-documented (often under a [[Creative Commons]] license<ref>[http://www.gogrid.com/company/press-releases/gogrid-moves-api-specification-to-creativecommons.php GoGrid Moves API Specification to Creative Commons]{{Dead link|date=August 2010}}</ref>) but also unique to their implementation and thus not interoperable. Some vendors have adopted others' APIs and there are a number of open standards under development, with a view to delivering interoperability and portability.<ref>{{cite web|url=http://ostatic.com/blog/eucalyptus-completes-amazon-web-services-specs-with-latest-release |title=Eucalyptus Completes Amazon Web Services Specs with Latest Release |publisher=Ostatic.com |date= |accessdate=2010-08-22}}</ref> As of November 2012, the Open Standard with broadest industry support is probably [[OpenStack]], founded in 2010 by [[NASA]] and [[Rackspace]], and now governed by the OpenStack Foundation.<ref>{{cite web|url=http://www.infoworld.com/d/cloud-computing/openstack-foundation-launches-202694/ |title=OpenStack Foundation launches |publisher=Infoworld.com |date=2012-09-19 |accessdate=2012-17-11}}</ref> [[OpenStack]]
supporters include [[AMD]], [[Intel]], [[Canonical Ltd.|Canonical]], [[SUSE Linux]], [[Red Hat]], [[Cisco]], [[Dell]], [[HP]], [[IBM]], [[Yahoo]] and now [[VMware]].<ref>{{cite web|url=http://www.informationweek.com/development/open-source/did-openstack-let-vmware-into-the-henhou/240009337 |title=Did OpenStack Let VMware Into The Henhouse? |publisher=Informationweek.com |date=2012-10-19 |accessdate=2012-17-11}}</ref>

===Security===
{{Main|Cloud computing security}}

As cloud computing is achieving increased popularity, concerns are being voiced about the security issues introduced through adoption of this new model. The effectiveness and efficiency of traditional protection mechanisms are being reconsidered as the characteristics of this innovative deployment model can differ widely from those of traditional architectures.<ref name="Zissis 10">{{cite journal|last=Zissis|first=Dimitrios|coauthors=Lekkas|title=Addressing cloud computing security issues|journal=Future Generation Computer Systems|year=2010|doi=10.1016/j.future.2010.12.006|url=http://www.sciencedirect.com/science/article/pii/S0167739X10002554|volume=28|issue=3|pages=583}}</ref> An alternative perspective on the topic of cloud security is that this is but another, although quite broad, case of "applied security" and that similar security principles that apply in shared multi-user mainframe security models apply with cloud security.<ref name="Securing The Cloud Winkler 2">{{cite book|last=Winkler|first=Vic|title=Securing the Cloud: Cloud Computer Security Techniques and Tactics|year=2011|publisher=Syngress|location=Waltham, MA USA|isbn=978-1-59749-592-9|pages=187, 189|url=http://www.elsevier.com/wps/find/bookdescription.cws_home/723529/description#description}}</ref>

The relative security of cloud computing services is a contentious issue that may be delaying its adoption.<ref>{{cite web|url=http://www.networkworld.com/news/2009/042709-burning-security-cloud-computing.html |title=Are security issues delaying adoption of cloud computing? |publisher=Network World |date= |accessdate=2010-08-22}}</ref> Physical control of the Private Cloud equipment is more secure than having the equipment off site and under someone else's control. Physical control and the ability to visually inspect data links and access ports is required in order to ensure data links are not compromised. Issues barring the adoption of cloud computing are due in large part to the private and public sectors' unease surrounding the external management of security-based services. It is the very nature of cloud computing-based services, private or public, that promote external management of provided services. This delivers great incentive to cloud computing service providers to prioritize building and maintaining strong management of secure services.<ref>{{cite web|url=http://www.networkworld.com/news/2010/022210-virtualization-cloud-security-debate.html |title=Security of virtualization, cloud computing divides IT and security pros |publisher=Network World |date=2010-02-22 |accessdate=2010-08-22}}</ref> Security issues have been categorised into sensitive data access, data segregation, privacy, bug exploitation, recovery, accountability, malicious insiders, management console security, account control, and multi-tenancy issues. Solutions to various cloud security issues vary, from cryptography, particularly public key infrastructure (PKI), to use of multiple cloud providers, standardisation of APIs, and improving virtual machine support and legal support.<ref name="Zissis 10" /><ref>{{cite journal|last=Armbrust|first=M|coauthors=Fox, A., Griffith, R., Joseph, A., Katz, R., Konwinski, A., Lee, G., Patterson, D., Rabkin, A., Zaharia,|title=A view of cloud computing|journal=Communication of the ACM|year=2010|volume=53|issue=4|pages=50–58|doi=10.1145/1721654.1721672}}</ref><ref>{{cite journal|last=Anthens|first=G|title=Security in the cloud|journal=Communications of the ACM|volume=53|issue=11|doi=10.1145/1839676.1839683|year=2010|pages=16}}</ref>

Cloud computing offers many benefits, but is vulnerable to threats. As cloud computing uses increase, it is likely that more criminals find new ways to exploit system vulnerabilities. Many underlying challenges and risks in cloud computing increase the threat of data compromise. To mitigate the threat, cloud computing stakeholders should invest heavily in risk assessment to ensure that the system encrypts to protect data, establishes trusted foundation to secure the platform and infrastructure, and builds higher assurance into auditing to strengthen compliance. Security concerns must be addressed to maintain trust in cloud computing technology.{{citation needed|date=February 2013}}

===Sustainability===
Although cloud computing is often assumed to be a form of ''[[green computing]]'', no published study substantiates this assumption.<ref>{{Cite news
| author = James Urquhart
| title = Cloud computing's green paradox
| quote =...&nbsp;there is some significant evidence that the cloud is encouraging more compute consumption
| publisher = CNET News
| date = January 7, 2010
| pages =
| url = http://news.cnet.com/8301-19413_3-10428065-240.html
| accessdate = March 12, 2010
}}</ref> Citing the servers' effects on the environmental effects of cloud computing, in areas where climate favors natural cooling and renewable electricity is readily available, the environmental effects will be more moderate. (The same holds true for "traditional" data centers.) Thus countries with favorable conditions, such as Finland,<ref>[http://www.fincloud.freehostingcloud.com/ Finland – First Choice for Siting Your Cloud Computing Data Center.]. Retrieved 4 August 2010.</ref> Sweden and Switzerland,<ref>[http://www.greenbiz.com/news/2010/06/30/swiss-carbon-neutral-servers-hit-cloud Swiss Carbon-Neutral Servers Hit the Cloud.]. Retrieved 4 August 2010.</ref> are trying to attract cloud computing data centers.
Energy efficiency in cloud computing can result from energy-aware [[scheduling (computing)|scheduling]] and server consolidation.<ref>Berl, Andreas, et al., [http://comjnl.oxfordjournals.org/content/53/7/1045.short Energy-Efficient Cloud Computing], The Computer Journal, 2010.</ref> However, in the case of distributed clouds over data centers with different source of energies including renewable source of energies, a small compromise on energy consumption reduction could result in high carbon footprint reduction.<ref>Farrahi Moghaddam, Fereydoun, et al., [http://ieeexplore.ieee.org/search/srchabstract.jsp?tp=&arnumber=6008718 Low Carbon Virtual Private Clouds], IEEE Cloud 2011.</ref>

===Abuse===
As with privately purchased hardware, customers can purchase the services of cloud computing for nefarious purposes. This includes password cracking and launching attacks using the purchased services.<ref>{{cite web|last=Alpeyev |first=Pavel |url=http://www.bloomberg.com/news/2011-05-13/sony-network-said-to-have-been-invaded-by-hackers-using-amazon-com-server.html |title=Amazon.com Server Said to Have Been Used in Sony Attack |publisher=Bloomberg |date=2011-05-14 |accessdate=2011-08-20}}</ref> In 2009, a banking [[Trojan horse (computing)|trojan]] illegally used the popular Amazon service as a command and control channel that issued software updates and malicious instructions to PCs that were infected by the malware.<ref>{{cite web|last=Goodin |first=Dan |url=http://www.theregister.co.uk/2011/05/14/playstation_network_attack_from_amazon/ |title=PlayStation Network hack launched from Amazon EC2 |publisher=The Register |date=2011-05-14 |accessdate=2012-05-18}}</ref>

===IT governance===
{{Main|Corporate governance of information technology}}

The introduction of cloud computing requires an appropriate IT governance model to ensure a secured computing environment and to comply with all relevant organizational information technology policies.<ref>Hsu, Wen-Hsi L., "Conceptual Framework of Cloud Computing Governance Model - An Education Perspective", IEEE Technology and Engineering Education (ITEE), Vol 7, No 2 (2012) [http://www.ewh.ieee.org/soc/e/sac/itee/index.php/meem/article/view/240]</ref><ref>Stackpole, Beth, "Governance Meets Cloud: Top Misconceptions", InformationWeek, 7 May 2012 [http://www.informationweek.com/cloud-computing/infrastructure/governance-meets-cloud-top-misconception/232901483]</ref> As such, organizations need a set of capabilities that are essential when effectively implementing and managing cloud services, including demand management, relationship management, data security management, application lifecycle management, risk and compliance management.<ref>Joha, A and M. Janssen (2012) "Transformation to Cloud Services Sourcing: Required IT Governance Capabilities", ICST Transactions on e-Business 12(7-9) [http://eudl.eu/pdf/10.4108/eb.2012.07-09.e4]</ref>
A danger lies with the explosion of companies joining the growth in cloud computing by becoming providers. However, many of the infrastructural and logistical concerns regarding the operation of cloud computing businesses are still unknown. This over-saturation may have ramifications for the industry as whole.<ref name="wired">[http://www.wired.com/insights/2013/01/beware-7-sins-of-cloud-computing Beware: 7 Sins of Cloud Computing]</ref>

===Consumer end storage===
The increased use of cloud computing could lead to a reduction in demand for high storage capacity consumer end devices, due to cheaper low storage devices that stream all content via the cloud becoming more popular.{{citation needed|date=February 2013}}
In a Wired article, Jake Gardner explains that while unregulated usage is beneficial for IT and tech moguls like Amazon, the anonymous nature of the cost of consumption of cloud usage makes it difficult for business to evaluate and incorporate it into their business plans.<ref name="wired" />

===Ambiguity of terminology===
Outside of the information technology and software industry, the term "cloud" can be found to reference a wide range of services, some of which fall under the category of cloud computing, while others do not. The cloud is often used to refer to a product or service that is discovered, accessed and paid for over the Internet, but is not necessarily a computing resource. Examples of service that are sometimes referred to as "the cloud" include, but are not limited to, [[crowd sourcing]], [[cloud printing]], [[crowd funding]], [[cloud manufacturing]].<ref>S. Stonham and S. Nahalkova (2012) "What is the Cloud and how can it help my business?" [http://www.ovasto.com/2013/01/what-is-the-cloud-how-can-the-cloud-help-my-business/]</ref><ref>S. Stonham and S. Nahalkova (2012), Whitepaper "Tomorrow Belongs to the Agile (PDF)" [http://www.ovasto.com/full-service-business-marketing-consultancy/strategic-agility-and-the-cloud/]</ref>

==Alternatives as normal user ==
Another possibility of cloud storage is to create your own cloud and keep the data on your own server (KYOD). Many manufacturers of home NAS devices provides this functionality out of the box. If you want to keep your data accessible at all times but don't trust the providers this is an viable option. The cons are that you have to secure the data on your end. The pros are that you know where your data is located. [http://personal-clouds.org/wiki/Main_Page]

==Origin of the cloud symbol==
The origin of the term ''cloud computing'' was derived from the practice of using drawings of stylized clouds to denote networks in diagrams of computing and communications systems. The word ''cloud'' was used as a metaphor for the Internet, based on the standardized use of a cloud-like shape to denote a network on telephony schematics and later to depict the Internet in [[computer network diagram]]s. The cloud symbol was used to represent the Internet as early as 1994.<ref>Figure 8, "A network 70 is shown schematically as a cloud", US Patent 5,485,455, column 17, line 22, filed Jan 28, 1994</ref><ref>Figure 1, "the cloud indicated at 49 in Fig. 1.", US Patent 5,790,548, column 5 line 56-57, filed April 18, 1996</ref> Servers were then shown connected to, but external to, the cloud symbol.

==Research==
Many universities, vendors and government organizations are investing in research around the topic of cloud computing:<ref>{{cite web|url=http://www.cloudbook.net/directories/research-clouds |title=Cloud Net Directory. Retrieved 2010-03-01 |publisher=Cloudbook.net |date= |accessdate=2010-08-22}}</ref><ref>{{cite web|url=http://www.nsf.gov/news/news_summ.jsp?cntn_id=114686 |title=– National Science Foundation (NSF) News – National Science Foundation Awards Millions to Fourteen Universities for Cloud Computing Research – US National Science Foun |publisher=Nsf.gov |date= |accessdate=2011-08-20}}</ref>

* In October 2007, the Academic Cloud Computing Initiative (ACCI) was announced as a multi-university project designed to enhance students' technical knowledge to address the challenges of cloud computing.<ref>{{cite web|url=http://www.datacenterknowledge.com/archives/2008/05/02/ibm-google-team-on-an-enterprise-cloud/ |title=IBM, Google Team on an Enterprise Cloud |date=2008-05-02 |author=Rich Miller |accessdate=2010-08-22 |publisher=DataCenterKnowledge.com}}</ref>

* In April 2009, UC Santa Barbara released the first open source platform-as-a-service, [[AppScale]], which is capable of running Google App Engine applications at scale on a multitude of infrastructures.

* In April 2009, the St Andrews Cloud Computing Co-laboratory was launched, focusing on research in the important new area of cloud computing. Unique in the UK, StACC aims to become an international centre of excellence for research and teaching in cloud computing and provides advice and information to businesses interested in cloud-based services.<ref>{{cite web|url=http://www.cs.st-andrews.ac.uk/stacc|title=StACC - Collaborative Research in Cloud Computing|publisher=University of St Andrews department of Computer Science|accessdate=2012-06-17}}</ref>

* In October 2010, the TClouds (Trustworthy Clouds) project was started, funded by the European Commission's 7th Framework Programme. The project's goal is to research and inspect the legal foundation and architectural design to build a resilient and trustworthy cloud-of-cloud infrastructure on top of that. The project also develops a prototype to demonstrate its results.<ref>{{cite web |url=http://www.tclouds-project.eu|title=Trustworthy Clouds: Privacy and Resilience for Internet-scale Critical Infrastructure|accessdate=2012-06-17}}</ref>

* In December 2010, the TrustCloud research project <ref name="communications2011">{{cite journal|last=Ko|first=Ryan K. L.|coauthors=Jagadpramana, Peter; Lee, Bu Sung|title=Flogger: A File-centric Logger for Monitoring File Access and Transfers within Cloud Computing Environments|journal=Proceedings of the 10th IEEE International Conference on Trust, Security and Privacy of Computing and Communications (TrustCom-11)|year=2011|url=http://www.hpl.hp.com/techreports/2011/HPL-2011-119.pdf|doi=10.1109/TrustCom.2011.100|isbn=978-1-4577-2135-9|pages=765}}</ref><ref>{{cite journal|last=Ko|first=Ryan K. L.|coauthors=Jagadpramana, Peter; Mowbray, Miranda; Pearson, Siani; Kirchberg, Markus; Liang, Qianhui; Lee, Bu Sung|title=TrustCloud: A Framework for Accountability and Trust in Cloud Computing|journal=Proceedings of the 2nd IEEE Cloud Forum for Practitioners (IEEE ICFP 2011), Washington DC, USA, July 7–8, 2011|year=2011|url=http://www.hpl.hp.com/techreports/2011/HPL-2011-38.pdf}}</ref> was started by HP Labs Singapore to address transparency and accountability of cloud computing via detective, data-centric approaches<ref>{{cite journal|last=Ko|first=Ryan K. L. Ko|coauthors=Kirchberg, Markus; Lee, Bu Sung|title=From System-Centric Logging to Data-Centric Logging - Accountability, Trust and Security in Cloud Computing|journal=Proceedings of the 1st Defence, Science and Research Conference 2011 - Symposium on Cyber Terrorism, IEEE Computer Society, 3–4 August 2011, Singapore|year=2011|url=http://www.hpl.hp.com/people/ryan_ko/RKo-DSR2011-Data_Centric_Logging.pdf}}</ref> encapsulated in a five-layer TrustCloud Framework. The team identified the need for monitoring data life cycles and transfers in the cloud,<ref name="communications2011"/> leading to the tackling of key cloud computing security issues such as cloud data leakages, cloud accountability and cross-national data transfers in transnational clouds.

* In June 2011, two Indian Universities i.e. [[University of Petroleum and Energy Studies]] and [[University of Technology and Management]] introduced cloud computing as a subject in India, in collaboration with [[IBM]].<ref>{{cite web|title=UTM/UPES-IBM India Collaboration |year=2011|url=http://www.youtube.com/watch?v=bDVKQKBN8XY}}</ref>

* In July 2011, the High Performance Computing Cloud (HPCCLoud) project was kicked-off aiming at finding out the possibilities of enhancing performance on cloud environments while running the scientific applications - development of HPCCLoud Performance Analysis Toolkit which was funded by CIM-Returning Experts Programme - under the coordination of Prof. Dr. Shajulin Benedict.

* In June 2011, the [[Telecommunications Industry Association]] developed a Cloud Computing White Paper, to analyze the integration challenges and opportunities between cloud services and traditional U.S. telecommunications standards.<ref>{{cite web|url=http://www.tiaonline.org/market_intelligence/publication_download.cfm?file=TIA_Cloud_Computing_White_Paper |title=Publication Download |publisher=Tiaonline.org |date= |accessdate=2011-12-02}}</ref>

* In February 2013, the BonFIRE project launched a multi-site cloud experimentation and testing facility. The facility provides transparent access to cloud resources, with the control and observability necessary to engineer future cloud technologies, in a way that is not restricted, for example, by current business models.<ref>{{cite web |url=http://www.bonfire-project.eu|title=Testbeds for cloud experimentation and testing|accessdate=2013-04-09}}</ref>

==See also==
*[[Cloud collaboration]]
*[[Cloud computing comparison]]
*[[Cloud telephony]]
*[[List of cloud computing conferences]]
*[[Mobile cloud computing]]
*[[Web operating system]]

==References==
{{Reflist|30em}}

==External links==
{{Commons category|Cloud computing}}
* [http://csrc.nist.gov/publications/nistpubs/800-145/SP800-145.pdf The NIST Definition of Cloud Computing]. Peter Mell and Timothy Grance, NIST Special Publication 800-145 (September 2011). National Institute of Standards and Technology, U.S. Department of Commerce.
* [http://nvlpubs.nist.gov/nistpubs/sp/2011/sp800-144.pdf Guidelines on Security and Privacy in Public Cloud Computing]. Wayne Jansen and Timothy Grance, NIST Special Publication 800-144 (December 2011). National Institute of Standards and Technology, U.S. Department of Commerce.
* [http://www.enisa.europa.eu/activities/risk-management/files/deliverables/cloud-computing-risk-assessment Cloud Computing - Benefits, risks and recommendation for information security]. Daniele Cattedu and Giles Hobben, European Network and Information Security Agency 2009.
* [http://www.europarl.europa.eu/committees/en/studiesdownload.html?languageDocument=EN&file=79050 Fighting cyber crime and protecting privacy in the cloud. European Parliament - Directorate-General for Internal Policies. 2012]
*[http://purl.fdlp.gov/GPO/gpo32975 Cloud Computing: What are the Security Implications?: Hearing before the Subcommittee on Cybersecurity, Infrastructure Protection, and Security Technologies of the Committee on Homeland Security, House of Representatives, One Hundred Twelfth Congress, First Session, October 6, 2011]
{{Cloud computing}}

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Revision as of 05:27, 13 May 2013

Cloud computing logical diagram

Cloud computing is the use of computing resources (hardware and software) which are available in a remote location and accessible over a network (typically the Internet). The name comes from the common use of a cloud-shaped symbol as an abstraction for the complex infrastructure it contains in system diagrams. Cloud computing entrusts remote services with a user's data, software and computation.

End users access cloud-based applications through a web browser or a light-weight desktop or mobile app while the business software and user's data are stored on servers at a remote location. Proponents claim that cloud computing allows companies to avoid upfront infrastructure costs, and focus on projects that differentiate their businesses instead of infrastructure.[1] Proponents also claim that cloud computing allows enterprises to get their applications up and running faster, with improved manageability and less maintenance, and enables IT to more rapidly adjust resources to meet fluctuating and unpredictable business demand.[1][2][3]

In the business model using software as a service (SaaS), users are provided access to application software and databases. Cloud providers manage the infrastructure and platforms that run the applications. SaaS is sometimes referred to as "on-demand software" and is usually priced on a pay-per-use basis. SaaS providers generally price applications using a subscription fee.

Proponents claim SaaS allows a business the potential to reduce IT operational costs by outsourcing hardware and software maintenance and support to the cloud provider. This enables the business to reallocate IT operations costs away from hardware/software spending and personnel expenses, towards meeting other goals. In addition, with applications hosted centrally, updates can be released without the need for users to install new software. One drawback of SaaS is that the users' data are stored on the cloud provider's server. As a result, there could be unauthorized access to the data.

Cloud computing relies on sharing of resources to achieve coherence and economies of scale similar to a utility (like the electricity grid) over a network.[4] At the foundation of cloud computing is the broader concept of converged infrastructure and shared services.

History

The underlying concept of cloud computing dates back to the 1950s, when large-scale mainframe became available in academia and corporations, accessible via thin clients / terminal computers, often referred to as "dumb terminals", because they were used for communications but had no internal computational capacities. To make more efficient use of costly mainframes, a practice evolved that allowed multiple users to share both the physical access to the computer from multiple terminals as well as to share the CPU time. This eliminated periods of inactivity on the mainframe and allowed for a greater return on the investment. The practice of sharing CPU time on a mainframe became known in the industry as time-sharing.[5]

In the 1990s, telecommunications companies, who previously offered primarily dedicated point-to-point data circuits, began offering virtual private network (VPN) services with comparable quality of service, but at a lower cost. By switching traffic as they saw fit to balance server use, they could use overall network bandwidth more effectively. They began to use the cloud symbol to denote the demarcation point between what the provider was responsible for and what users were responsible for. Cloud computing extends this boundary to cover servers as well as the network infrastructure.[6]

As computers became more prevalent, scientists and technologists explored ways to make large-scale computing power available to more users through time sharing, experimenting with algorithms to provide the optimal use of the infrastructure, platform and applications with prioritized access to the CPU and efficiency for the end users.[7]

John McCarthy opined in the 1960s that "computation may someday be organized as a public utility." [17] Almost all the modern-day characteristics of cloud computing (elastic provision, provided as a utility, online, illusion of infinite supply), the comparison to the electricity industry and the use of public, private, government, and community forms, were thoroughly explored in Douglas Parkhill's 1966 book, The Challenge of the Computer Utility. Other scholars have shown that cloud computing's roots go all the way back to the 1950s when scientist Herb Grosch (the author of Grosch's law) postulated that the entire world would operate on dumb terminals powered by about 15 large data centers.[8] Due to the expense of these powerful computers, many corporations and other entities could avail themselves of computing capability through time sharing and several organizations, such as GE's GEISCO, IBM subsidiary The Service Bureau Corporation (SBC, founded in 1957), Tymshare (founded in 1966), National CSS (founded in 1967 and bought by Dun & Bradstreet in 1979), Dial Data (bought by Tymshare in 1968), and Bolt, Beranek and Newman (BBN) marketed time sharing as a commercial venture.

The development of the Internet from being document centric via semantic data towards more and more services was described as "Dynamic Web".[9] This contribution focused in particular in the need for better meta-data able to describe not only implementation details but also conceptual details of model-based applications.

The ubiquitous availability of high-capacity networks, low-cost computers and storage devices as well as the widespread adoption of hardware virtualization, service-oriented architecture, autonomic, and utility computing have led to a tremendous growth in cloud computing.[10][11][12]

After the dot-com bubble, Amazon played a key role in the development of cloud computing by modernizing their data centers, which, like most computer networks, were using as little as 10% of their capacity at any one time, just to leave room for occasional spikes. Having found that the new cloud architecture resulted in significant internal efficiency improvements whereby small, fast-moving "two-pizza teams" (teams small enough to feed with two pizzas) could add new features faster and more easily, Amazon initiated a new product development effort to provide cloud computing to external customers, and launched Amazon Web Service (AWS) on a utility computing basis in 2006.[13][14]

In early 2008, Eucalyptus became the first open-source, AWS API-compatible platform for deploying private clouds. In early 2008, OpenNebula, enhanced in the RESERVOIR European Commission-funded project, became the first open-source software for deploying private and hybrid clouds, and for the federation of clouds.[15] In the same year, efforts were focused on providing quality of service guarantees (as required by real-time interactive applications) to cloud-based infrastructures, in the framework of the IRMOS European Commission-funded project, resulting to a real-time cloud environment.[16] By mid-2008, Gartner saw an opportunity for cloud computing "to shape the relationship among consumers of IT services, those who use IT services and those who sell them"[17] and observed that "organizations are switching from company-owned hardware and software assets to per-use service-based models" so that the "projected shift to computing ... will result in dramatic growth in IT products in some areas and significant reductions in other areas."[18]

On March 1, 2011, IBM announced the IBM SmartCloud framework to support Smarter Planet.[19] Among the various components of the Smarter Computing foundation, cloud computing is a critical piece.

Similar systems and concepts

Cloud Computing is the result of evolution and adoption of existing technologies and paradigms. The goal of cloud computing is to allow users to take benefit from all of these technologies, without the need for deep knowledge about or expertise with each one of them. The cloud aims to cut costs, and help the users focus on their core business instead of being impeded by IT obstacles.[20]

The main enabling technology for cloud computing is virtualization. Virtualization abstracts the physical infrastructure, which is the most rigid component, and makes it available as a soft component that is easy to use and manage. By doing so, virtualization provides the agility required to speed up IT operations, and reduces cost by increasing infrastructure utilization. On the other hand, autonomic computing automates the process through which the user can provision resources on-demand. By minimizing user involvement, automation speeds up the process and reduces the possibility of human errors.[20]

Users face difficult business problems every day. Cloud computing adopts concepts from Service-oriented Architecture (SOA) that can help the user break these problems into services that can be integrated to provide a solution. Cloud computing provides all of its resources as services, and makes use of the well-established standards and best practices gained in the domain of SOA to allow global and easy access to cloud services in a standardized way.

Cloud computing also leverages concepts from utility computing in order to provide metrics for the services used. Such metrics are at the core of the public cloud pay-per-use models. In addition, measured services are an essential part of the feedback loop in autonomic computing, allowing services to scale on-demand and to perform automatic failure recovery.

Cloud computing is a kind of grid computing; it has evolved from grid computing by addressing the QoS (quality of service) and reliability problems. Cloud computing provides the tools and technologies to build data/compute intensive parallel applications with much more affordable prices compared to traditional parallel computing techniques.[20]

Cloud computing shares characteristics with:

  • Client–server modelClient–server computing refers broadly to any distributed application that distinguishes between service providers (servers) and service requesters (clients).[21]
  • Grid computing — "A form of distributed and parallel computing, whereby a 'super and virtual computer' is composed of a cluster of networked, loosely coupled computers acting in concert to perform very large tasks."
  • Mainframe computer — Powerful computers used mainly by large organizations for critical applications, typically bulk data processing such as census, industry and consumer statistics, police and secret intelligence services, enterprise resource planning, and financial transaction processing.[22]
  • Utility computing — The "packaging of computing resources, such as computation and storage, as a metered service similar to a traditional public utility, such as electricity."[23][24]
  • Peer-to-peer means distributed architecture without the need for central coordination. Participants are both suppliers and consumers of resources (in contrast to the traditional client–server model).
  • Cloud gaming—also known as on-demand gaming—is a way of delivering games to computers. Gaming data is stored in the provider's server, so that gaming is independent of client computers used to play the game.

Characteristics

Cloud computing exhibits the following key characteristics:

  • Agility improves with users' ability to re-provision technological infrastructure resources.
  • Application programming interface (API) accessibility to software that enables machines to interact with cloud software in the same way that a traditional user interface (e.g., a computer desktop) facilitates interaction between humans and computers. Cloud computing systems typically use Representational State Transfer (REST)-based APIs.
  • Cost is claimed to be reduced, and in a public cloud delivery model capital expenditure is converted to operational expenditure.[25] This is purported to lower barriers to entry, as infrastructure is typically provided by a third-party and does not need to be purchased for one-time or infrequent intensive computing tasks. Pricing on a utility computing basis is fine-grained with usage-based options and fewer IT skills are required for implementation (in-house).[26] The e-FISCAL project's state of the art repository[27] contains several articles looking into cost aspects in more detail, most of them concluding that costs savings depend on the type of activities supported and the type of infrastructure available in-house.
  • Device and location independence[28] enable users to access systems using a web browser regardless of their location or what device they are using (e.g., PC, mobile phone). As infrastructure is off-site (typically provided by a third-party) and accessed via the Internet, users can connect from anywhere.[26]
  • Virtualization technology allows servers and storage devices to be shared and utilization be increased. Applications can be easily migrated from one physical server to another.
  • Multitenancy enables sharing of resources and costs across a large pool of users thus allowing for:
    • Centralization of infrastructure in locations with lower costs (such as real estate, electricity, etc.)
    • Peak-load capacity increases (users need not engineer for highest possible load-levels)
    • Utilisation and efficiency improvements for systems that are often only 10–20% utilised.[13][29]
  • Reliability is improved if multiple redundant sites are used, which makes well-designed cloud computing suitable for business continuity and disaster recovery.[30]
  • Scalability and elasticity via dynamic ("on-demand") provisioning of resources on a fine-grained, self-service basis near real-time,[31][32] without users having to engineer for peak loads.[33][34][35]
  • Performance is monitored, and consistent and loosely coupled architectures are constructed using web services as the system interface.[26]
  • Security could improve due to centralization of data, increased security-focused resources, etc., but concerns can persist about loss of control over certain sensitive data, and the lack of security for stored kernels.[36] Security is often as good as or better than other traditional systems, in part because providers are able to devote resources to solving security issues that many customers cannot afford.[37] However, the complexity of security is greatly increased when data is distributed over a wider area or greater number of devices and in multi-tenant systems that are being shared by unrelated users. In addition, user access to security audit logs may be difficult or impossible. Private cloud installations are in part motivated by users' desire to retain control over the infrastructure and avoid losing control of information security.
  • Maintenance of cloud computing applications is easier, because they do not need to be installed on each user's computer and can be accessed from different places.

The National Institute of Standards and Technology's definition of cloud computing identifies "five essential characteristics":

On-demand self-service. A consumer can unilaterally provision computing capabilities, such as server time and network storage, as needed automatically without requiring human interaction with each service provider.

Broad network access. Capabilities are available over the network and accessed through standard mechanisms that promote use by heterogeneous thin or thick client platforms (e.g., mobile phones, tablets, laptops, and workstations).

Resource pooling. The provider's computing resources are pooled to serve multiple consumers using a multi-tenant model, with different physical and virtual resources dynamically assigned and reassigned according to consumer demand. ...

Rapid elasticity. Capabilities can be elastically provisioned and released, in some cases automatically, to scale rapidly outward and inward commensurate with demand. To the consumer, the capabilities available for provisioning often appear unlimited and can be appropriated in any quantity at any time.

Measured service. Cloud systems automatically control and optimize resource use by leveraging a metering capability at some level of abstraction appropriate to the type of service (e.g., storage, processing, bandwidth, and active user accounts). Resource usage can be monitored, controlled, and reported, providing transparency for both the provider and consumer of the utilized service.

— National Institute of Standards and Technology[4]

On-demand self-service

On-demand self-service allows users to obtain, configure and deploy cloud services themselves using cloud service catalogues, without requiring the assistance of IT.[38][39] This feature is listed by the National Institute of Standards and Technology (NIST) as a characteristic of cloud computing.[4]

The self-service requirement of cloud computing prompts infrastructure vendors to create cloud computing templates, which are obtained from cloud service catalogues. Manufacturers of such templates or blueprints include BMC Software (BMC), with Service Blueprints as part of their cloud management platform[40] Hewlett-Packard (HP), which names its templates as HP Cloud Maps[41] RightScale[42] and Red Hat, which names its templates CloudForms.[43]

The templates contain predefined configurations used by consumers to set up cloud services. The templates or blueprints provide the technical information necessary to build ready-to-use clouds.[42] Each template includes specific configuration details for different cloud infrastructures, with information about servers for specific tasks such as hosting applications, databases, websites and so on.[42] The templates also include predefined Web service, the operating system, the database, security configurations and load balancing.[43]

Cloud computing consumers use cloud templates to move applications between clouds through a self-service portal. The predefined blueprints define all that an application requires to run in different environments. For example, a template could define how the same application could be deployed in cloud platforms based on Amazon Web Service, VMware or Red Hat.[44] The user organization benefits from cloud templates because the technical aspects of cloud configurations reside in the templates, letting users to deploy cloud services with a push of a button.[45][46] Cloud templates can also be used by developers to create a catalog of cloud services.[47]

Service models

Cloud computing providers offer their services according to several fundamental models:[4][48] infrastructure as a service (IaaS), platform as a service (PaaS), and software as a service (SaaS) where IaaS is the most basic and each higher model abstracts from the details of the lower models. Other key components in XaaS are described in a comprehensive taxonomy model published in 2009,[49] such as Strategy-as-a-Service, Collaboration-as-a-Service, Business Process-as-a-Service, Database-as-a-Service, etc. In 2012, network as a service (NaaS) and communication as a service (CaaS) were officially included by ITU (International Telecommunication Union) as part of the basic cloud computing models, recognized service categories of a telecommunication-centric cloud ecosystem.[50]

Infrastructure as a service (IaaS)

In the most basic cloud-service model, providers of IaaS offer computers - physical or (more often) virtual machines - and other resources. (A hypervisor, such as Xen or KVM, runs the virtual machines as guests. Pools of hypervisors within the cloud operational support-system can support large numbers of virtual machines and the ability to scale services up and down according to customers' varying requirements.) IaaS clouds often offer additional resources such as a virtual-machine disk image library, raw (block) and file-based storage, firewalls, load balancers, IP addresses, virtual local area networks (VLANs), and software bundles.[51] IaaS-cloud providers supply these resources on-demand from their large pools installed in data centers. For wide-area connectivity, customers can use either the Internet or carrier clouds (dedicated virtual private networks).

To deploy their applications, cloud users install operating-system images and their application software on the cloud infrastructure. In this model, the cloud user patches and maintains the operating systems and the application software. Cloud providers typically bill IaaS services on a utility computing basis[citation needed]: cost reflects the amount of resources allocated and consumed.

Examples of IaaS providers include: Amazon EC2, AirVM, Azure Services Platform, DynDNS, Google Compute Engine, HP Cloud, iland, Joyent, LeaseWeb, Linode, NaviSite, Oracle Infrastructure as a Service, Rackspace, ReadySpace Cloud Services, ReliaCloud, SAVVIS, SingleHop, and Terremark

Cloud communications and cloud telephony, rather than replacing local computing infrastructure, replace local telecommunications infrastructure with Voice over IP and other off-site Internet services.

Platform as a service (PaaS)

In the PaaS model, cloud providers deliver a computing platform typically including operating system, programming language execution environment, database, and web server. Application developers can develop and run their software solutions on a cloud platform without the cost and complexity of buying and managing the underlying hardware and software layers. With some PaaS offers, the underlying computer and storage resources scale automatically to match application demand such that cloud user does not have to allocate resources manually.

Examples of PaaS include: AWS Elastic Beanstalk, Cloud Foundry, Heroku, Force.com, EngineYard, Mendix, OpenShift, Google App Engine, Windows Azure Cloud Services and OrangeScape.

Software as a service (SaaS)

In the SaaS model, cloud providers install and operate application software in the cloud and cloud users access the software from cloud clients. Cloud users do not manage the cloud infrastructure and platform where the application runs. This eliminates the need to install and run the application on the cloud user's own computers, which simplifies maintenance and support. Cloud applications are different from other applications in their scalability—which can be achieved by cloning tasks onto multiple virtual machines at run-time to meet changing work demand.[52] Load balancers distribute the work over the set of virtual machines. This process is transparent to the cloud user, who sees only a single access point. To accommodate a large number of cloud users, cloud applications can be multitenant, that is, any machine serves more than one cloud user organization. It is common to refer to special types of cloud based application software with a similar naming convention: desktop as a service, business process as a service, test environment as a service, communication as a service.

The pricing model for SaaS applications is typically a monthly or yearly flat fee per user,[53] so price is scalable and adjustable if users are added or removed at any point.[54]

Examples of SaaS include: Google Apps, Microsoft Office 365, Onlive, GT Nexus, Marketo, Casengo and TradeCard.

Network as a service (NaaS)

A category of cloud services where the capability provided to the cloud service user is to use network/transport connectivity services and/or inter-cloud network connectivity services.[55] NaaS involves the optimization of resource allocations by considering network and computing resources as a unified whole.[56]

Traditional NaaS services include flexible and extended VPN, and bandwidth on demand.[55] NaaS concept materialization also includes the provision of a virtual network service by the owners of the network infrastructure to a third party (VNP – VNO).[57][58]

Cloud clients

Users access cloud computing using networked client devices, such as desktop computers, laptops, tablets and smartphones. Some of these devices - cloud clients - rely on cloud computing for all or a majority of their applications so as to be essentially useless without it. Examples are thin clients and the browser-based Chromebook. Many cloud applications do not require specific software on the client and instead use a web browser to interact with the cloud application. With Ajax and HTML5 these Web user interfaces can achieve a similar, or even better, look and feel to native applications. Some cloud applications, however, support specific client software dedicated to these applications (e.g., virtual desktop clients and most email clients). Some legacy applications (line of business applications that until now have been prevalent in thin client Windows computing) are delivered via a screen-sharing technology.

Deployment models

Cloud computing types

Public cloud

Public cloud applications, storage, and other resources are made available to the general public by a service provider. These services are free or offered on a pay-per-use model. Generally, public cloud service providers like Amazon AWS, Microsoft and Google own and operate the infrastructure and offer access only via Internet (direct connectivity is not offered).[26]

Community cloud

Community cloud shares infrastructure between several organizations from a specific community with common concerns (security, compliance, jurisdiction, etc.), whether managed internally or by a third-party and hosted internally or externally. The costs are spread over fewer users than a public cloud (but more than a private cloud), so only some of the cost savings potential of cloud computing are realized.[4]

Hybrid cloud

Hybrid cloud is a composition of two or more clouds (private, community or public) that remain unique entities but are bound together, offering the benefits of multiple deployment models.[4] Such composition expands deployment options for cloud services, allowing IT organizations to use public cloud computing resources to meet temporary needs.[59] This capability enables hybrid clouds to employ cloud bursting for scaling across clouds.[4]

Cloud bursting is an application deployment model in which an application runs in a private cloud or data center and "bursts" to a public cloud when the demand for computing capacity increases. A primary advantage of cloud bursting and a hybrid cloud model is that an organization only pays for extra compute resources when they are needed.[60]

Cloud bursting enables data centers to create an in-house IT infrastructure that supports average workloads, and use cloud resources from public or private clouds, during spikes in processing demands.[61]

By utilizing "hybrid cloud" architecture, companies and individuals are able to obtain degrees of fault tolerance combined with locally immediate usability without dependency on internet connectivity. Hybrid cloud architecture requires both on-premises resources and off-site (remote) server-based cloud infrastructure.

Hybrid clouds lack the flexibility, security and certainty of in-house applications.[62] Hybrid cloud provides the flexibility of in house applications with the fault tolerance and scalability of cloud based services.

Private cloud

Private cloud is cloud infrastructure operated solely for a single organization, whether managed internally or by a third-party and hosted internally or externally.[4] Undertaking a private cloud project requires a significant level and degree of engagement to virtualize the business environment, and requires the organization to reevaluate decisions about existing resources. When done right, it can improve business, but every step in the project raises security issues that must be addressed to prevent serious vulnerabilities.[63]

They have attracted criticism because users "still have to buy, build, and manage them" and thus do not benefit from less hands-on management,[64] essentially "[lacking] the economic model that makes cloud computing such an intriguing concept".[65][66]

Comparison for SaaS
Public cloud Private cloud
Initial cost Typically zero Typically high
Running cost Predictable Unpredictable
Customization Impossible Possible
Privacy No (Host has access to the data) Yes
Single sign-on Impossible Possible
Scaling up Easy while within defined limits Laborious but no limits

Architecture

Cloud computing sample architecture

Cloud architecture,[67] the systems architecture of the software systems involved in the delivery of cloud computing, typically involves multiple cloud components communicating with each other over a loose coupling mechanism such as a messaging queue. Elastic provision implies intelligence in the use of tight or loose coupling as applied to mechanisms such as these and others.

The Intercloud

The Intercloud[68] is an interconnected global "cloud of clouds"[69][70] and an extension of the Internet "network of networks" on which it is based.[71][72][73]

Cloud engineering

Cloud engineering is the application of engineering disciplines to cloud computing. It brings a systematic approach to the high-level concerns of commercialisation, standardisation, and governance in conceiving, developing, operating and maintaining cloud computing systems. It is a multidisciplinary method encompassing contributions from diverse areas such as systems, software, web, performance, information, security, platform, risk, and quality engineering.

Issues

Threats and opportunities of the cloud

56% of European decision-makers estimate that the cloud is a priority between 2013 and 2014.[74] The cloud budget should reach 30% of the overall IT budget.[citation needed] But several deterrents to the cloud remain. Among them, are: reliability, availability of services and data, security, complexity, costs, regulations and legal issues, performance, migration, reversion, the lack of standards, and limited customization. The cloud also offers several strong points, however: infrastructure flexibility, faster deployment of applications and data, cost control, adaptation of cloud resources to real needs, improved productivity, etc. The early 2010s cloud market is dominated by software and services in SaaS mode and IaaS (infrastructure), especially the private cloud. PaaS and the public cloud are further back.

Privacy

Privacy advocates have criticized the cloud model for hosting companies' greater ease can control—and thus, can monitor at will—communication between host company and end user, and access user data (with or without permission). Instances such as the secret NSA program, working with AT&T, and Verizon, which recorded over 10 million telephone calls between American citizens, causes uncertainty among privacy advocates, and the greater powers it gives to telecommunication companies to monitor user activity.[75] A cloud service provider (CSP) can complicate data privacy because of the extent of virtualization (virtual machines) and cloud storage used to implement cloud service.[76] CSP operations, customer or tenant data may not remain on the same system, or in the same data center or even within the same provider's cloud; this can lead to legal concerns over jurisdiction. While there have been efforts (such as US-EU Safe Harbor) to "harmonise" the legal environment, providers such as Amazon still cater to major markets (typically the United States and the European Union) by deploying local infrastructure and allowing customers to select "availability zones."[77] Cloud computing poses privacy concerns because the service provider may access the data that is on the cloud at any point in time. They could accidentally or deliberately alter or even delete information.[78]

Postage and delivery services company Pitney Bowes launched Volly, a cloud-based, digital mailbox service to leverage its communication management assets. They also faced the technical challenge of providing strong data security and privacy. However, they were able to address the same concern by applying customized, application-level security, including encryption.[79]

Compliance

To comply with regulations including FISMA, HIPAA, and SOX in the United States, the Data Protection Directive in the EU and the credit card industry's PCI DSS, users may have to adopt community or hybrid deployment modes that are typically more expensive and may offer restricted benefits. This is how Google is able to "manage and meet additional government policy requirements beyond FISMA"[80][81] and Rackspace Cloud or QubeSpace are able to claim PCI compliance.[82]

Many providers also obtain a SAS 70 Type II audit, but this has been criticised on the grounds that the hand-picked set of goals and standards determined by the auditor and the auditee are often not disclosed and can vary widely.[83] Providers typically make this information available on request, under non-disclosure agreement.[84][85]

Customers in the EU contracting with cloud providers outside the EU/EEA have to adhere to the EU regulations on export of personal data.[86]

U.S. Federal Agencies have been directed by the Office of Management and Budget to use a process called FedRAMP (Federal Risk and Authorization Management Program) to assess and authorize cloud products and services. Federal CIO Steven VanRoekel issued a memorandum to federal agency Chief Information Officers on December 8, 2011 defining how federal agencies should use FedRAMP. FedRAMP consists of a subset of NIST Special Publication 800-53 security controls specifically selected to provide protection in cloud environments. A subset has been defined for the FIPS 199 low categorization and the FIPS 199 moderate categorization. The FedRAMP program has also established a Joint Accreditation Board (JAB) consisting of Chief Information Officers from DoD, DHS and GSA. The JAB is responsible for establishing accreditation standards for 3rd party organizations who perform the assessments of cloud solutions. The JAB also reviews authorization packages, and may grant provisional authorization (to operate). The federal agency consuming the service still has final responsibility for final authority to operate.[87]

A multitude of laws and regulations have forced specific compliance requirements onto many companies that collect, generate or store data. These policies may dictate a wide array of data storage policies, such as how long information must be retained, the process used for deleting data, and even certain recovery plans. Below are some examples of compliance laws or regulations.

  • In the United States, the Health Insurance Portability and Accountability Act (HIPAA) requires a contingency plan that includes, data backups, data recovery, and data access during emergencies.
  • The privacy laws of the Switzerland demand that private data, including emails, be physically stored in the Switzerland.
  • In the United Kingdom, the Civil Contingencies Act of 2004 sets forth guidance for a Business contingency plan that includes policies for data storage.

In a virtualized cloud computing environment, customers may never know exactly where their data is stored. In fact, data may be stored across multiple data centers in an effort to improve reliability, increase performance, and provide redundancies. This geographic dispersion may make it more difficult to ascertain legal jurisdiction if disputes arise.[88]

As with other changes in the landscape of computing, certain legal issues arise with cloud computing, including trademark infringement, security concerns and sharing of proprietary data resources.

The Electronic Frontier Foundation has criticized the United States government for considering during the Megaupload seizure process that people lose property rights by storing data on a cloud computing service.[89]

One important but not often mentioned problem with cloud computing is the problem of who is in "possession" of the data. If a cloud company is the possessor of the data, the possessor has certain legal rights. If the cloud company is the "custodian" of the data, then a different set of rights would apply. The next problem in the legalities of cloud computing is the problem of legal ownership of the data. Many Terms of Service agreements are silent on the question of ownership.[90]

These legal issues are not confined to the time period in which the cloud based application is actively being used. There must also be consideration for what happens when the provider-customer relationship ends. In most cases, this event will be addressed before an application is deployed to the cloud. However, in the case of provider insolvencies or bankruptcy the state of the data may become blurred.[88]

Vendor lock-in

Because cloud computing is still relatively new, standards are still being developed.[91] Many cloud platforms and services are proprietary, meaning that they are built on the specific standards, tools and protocols developed by a particular vendor for its particular cloud offering.[91] This can make migrating off a proprietary cloud platform prohibitively complicated and expensive.[91]

Three types of vendor lock-in can occur with cloud computing:[92]

  • Platform lock-in: cloud services tend to be built on one of several possible virtualization platforms, for example VMWare or Xen. Migrating from a cloud provider using one platform to a cloud provider using a different platform could be very complicated.
  • Data lock-in: since the cloud is still new, standards of ownership, i.e. who actually owns the data once it lives on a cloud platform, are not yet developed, which could make it complicated if cloud computing users ever decide to move data off of a cloud vendor's platform.
  • Tools lock-in: if tools built to manage a cloud environment are not compatible with different kinds of both virtual and physical infrastructure, those tools will only be able to manage data or apps that live in the vendor's particular cloud environment.

Heterogeneous cloud computing is described as a type of cloud environment that prevents vendor lock-in, and aligns with enterprise data centers that are operating hybrid cloud models.[93] The absence of vendor lock-in lets cloud administrators select his or her choice of hypervisors for specific tasks, or to deploy virtualized infrastructures to other enterprises without the need to consider the flavor of hypervisor in the other enterprise.[94]

A heterogeneous cloud is considered one that includes on-premise private clouds, public clouds and software-as-a-service clouds. Heterogeneous clouds can work with environments that are not virtualized, such as traditional data centers.[95] Heterogeneous clouds also allow for the use of piece parts, such as hypervisors, servers, and storage, from multiple vendors.[96]

Cloud piece parts, such as cloud storage systems, offer APIs but they are often incompatible with each other.[97] The result is complicated migration between backends, and makes it difficult to integrate data spread across various locations.[97] This has been described as a problem of vendor lock-in.[97] The solution to this is for clouds to adopt common standards.[97]

Heterogeneous cloud computing differs from homogeneous clouds, which have been described as those using consistent building blocks supplied by a single vendor.[98] Intel General Manager of high-density computing, Jason Waxman, is quoted as saying that a homogenous system of 15,000 servers would cost $6 million more in capital expenditure and use 1 megawatt of power.[98]

Open source

Open-source software has provided the foundation for many cloud computing implementations, prominent examples being the Hadoop framework[99] and VMware's Cloud Foundry.[100] In November 2007, the Free Software Foundation released the Affero General Public License, a version of GPLv3 intended to close a perceived legal loophole associated with free software designed to run over a network.[101]

Open standards

Most cloud providers expose APIs that are typically well-documented (often under a Creative Commons license[102]) but also unique to their implementation and thus not interoperable. Some vendors have adopted others' APIs and there are a number of open standards under development, with a view to delivering interoperability and portability.[103] As of November 2012, the Open Standard with broadest industry support is probably OpenStack, founded in 2010 by NASA and Rackspace, and now governed by the OpenStack Foundation.[104] OpenStack supporters include AMD, Intel, Canonical, SUSE Linux, Red Hat, Cisco, Dell, HP, IBM, Yahoo and now VMware.[105]

Security

As cloud computing is achieving increased popularity, concerns are being voiced about the security issues introduced through adoption of this new model. The effectiveness and efficiency of traditional protection mechanisms are being reconsidered as the characteristics of this innovative deployment model can differ widely from those of traditional architectures.[106] An alternative perspective on the topic of cloud security is that this is but another, although quite broad, case of "applied security" and that similar security principles that apply in shared multi-user mainframe security models apply with cloud security.[107]

The relative security of cloud computing services is a contentious issue that may be delaying its adoption.[108] Physical control of the Private Cloud equipment is more secure than having the equipment off site and under someone else's control. Physical control and the ability to visually inspect data links and access ports is required in order to ensure data links are not compromised. Issues barring the adoption of cloud computing are due in large part to the private and public sectors' unease surrounding the external management of security-based services. It is the very nature of cloud computing-based services, private or public, that promote external management of provided services. This delivers great incentive to cloud computing service providers to prioritize building and maintaining strong management of secure services.[109] Security issues have been categorised into sensitive data access, data segregation, privacy, bug exploitation, recovery, accountability, malicious insiders, management console security, account control, and multi-tenancy issues. Solutions to various cloud security issues vary, from cryptography, particularly public key infrastructure (PKI), to use of multiple cloud providers, standardisation of APIs, and improving virtual machine support and legal support.[106][110][111]

Cloud computing offers many benefits, but is vulnerable to threats. As cloud computing uses increase, it is likely that more criminals find new ways to exploit system vulnerabilities. Many underlying challenges and risks in cloud computing increase the threat of data compromise. To mitigate the threat, cloud computing stakeholders should invest heavily in risk assessment to ensure that the system encrypts to protect data, establishes trusted foundation to secure the platform and infrastructure, and builds higher assurance into auditing to strengthen compliance. Security concerns must be addressed to maintain trust in cloud computing technology.[citation needed]

Sustainability

Although cloud computing is often assumed to be a form of green computing, no published study substantiates this assumption.[112] Citing the servers' effects on the environmental effects of cloud computing, in areas where climate favors natural cooling and renewable electricity is readily available, the environmental effects will be more moderate. (The same holds true for "traditional" data centers.) Thus countries with favorable conditions, such as Finland,[113] Sweden and Switzerland,[114] are trying to attract cloud computing data centers. Energy efficiency in cloud computing can result from energy-aware scheduling and server consolidation.[115] However, in the case of distributed clouds over data centers with different source of energies including renewable source of energies, a small compromise on energy consumption reduction could result in high carbon footprint reduction.[116]

Abuse

As with privately purchased hardware, customers can purchase the services of cloud computing for nefarious purposes. This includes password cracking and launching attacks using the purchased services.[117] In 2009, a banking trojan illegally used the popular Amazon service as a command and control channel that issued software updates and malicious instructions to PCs that were infected by the malware.[118]

IT governance

The introduction of cloud computing requires an appropriate IT governance model to ensure a secured computing environment and to comply with all relevant organizational information technology policies.[119][120] As such, organizations need a set of capabilities that are essential when effectively implementing and managing cloud services, including demand management, relationship management, data security management, application lifecycle management, risk and compliance management.[121] A danger lies with the explosion of companies joining the growth in cloud computing by becoming providers. However, many of the infrastructural and logistical concerns regarding the operation of cloud computing businesses are still unknown. This over-saturation may have ramifications for the industry as whole.[122]

Consumer end storage

The increased use of cloud computing could lead to a reduction in demand for high storage capacity consumer end devices, due to cheaper low storage devices that stream all content via the cloud becoming more popular.[citation needed] In a Wired article, Jake Gardner explains that while unregulated usage is beneficial for IT and tech moguls like Amazon, the anonymous nature of the cost of consumption of cloud usage makes it difficult for business to evaluate and incorporate it into their business plans.[122]

Ambiguity of terminology

Outside of the information technology and software industry, the term "cloud" can be found to reference a wide range of services, some of which fall under the category of cloud computing, while others do not. The cloud is often used to refer to a product or service that is discovered, accessed and paid for over the Internet, but is not necessarily a computing resource. Examples of service that are sometimes referred to as "the cloud" include, but are not limited to, crowd sourcing, cloud printing, crowd funding, cloud manufacturing.[123][124]

Alternatives as normal user

Another possibility of cloud storage is to create your own cloud and keep the data on your own server (KYOD). Many manufacturers of home NAS devices provides this functionality out of the box. If you want to keep your data accessible at all times but don't trust the providers this is an viable option. The cons are that you have to secure the data on your end. The pros are that you know where your data is located. [18]

Origin of the cloud symbol

The origin of the term cloud computing was derived from the practice of using drawings of stylized clouds to denote networks in diagrams of computing and communications systems. The word cloud was used as a metaphor for the Internet, based on the standardized use of a cloud-like shape to denote a network on telephony schematics and later to depict the Internet in computer network diagrams. The cloud symbol was used to represent the Internet as early as 1994.[125][126] Servers were then shown connected to, but external to, the cloud symbol.

Research

Many universities, vendors and government organizations are investing in research around the topic of cloud computing:[127][128]

  • In October 2007, the Academic Cloud Computing Initiative (ACCI) was announced as a multi-university project designed to enhance students' technical knowledge to address the challenges of cloud computing.[129]
  • In April 2009, UC Santa Barbara released the first open source platform-as-a-service, AppScale, which is capable of running Google App Engine applications at scale on a multitude of infrastructures.
  • In April 2009, the St Andrews Cloud Computing Co-laboratory was launched, focusing on research in the important new area of cloud computing. Unique in the UK, StACC aims to become an international centre of excellence for research and teaching in cloud computing and provides advice and information to businesses interested in cloud-based services.[130]
  • In October 2010, the TClouds (Trustworthy Clouds) project was started, funded by the European Commission's 7th Framework Programme. The project's goal is to research and inspect the legal foundation and architectural design to build a resilient and trustworthy cloud-of-cloud infrastructure on top of that. The project also develops a prototype to demonstrate its results.[131]
  • In December 2010, the TrustCloud research project [132][133] was started by HP Labs Singapore to address transparency and accountability of cloud computing via detective, data-centric approaches[134] encapsulated in a five-layer TrustCloud Framework. The team identified the need for monitoring data life cycles and transfers in the cloud,[132] leading to the tackling of key cloud computing security issues such as cloud data leakages, cloud accountability and cross-national data transfers in transnational clouds.
  • In July 2011, the High Performance Computing Cloud (HPCCLoud) project was kicked-off aiming at finding out the possibilities of enhancing performance on cloud environments while running the scientific applications - development of HPCCLoud Performance Analysis Toolkit which was funded by CIM-Returning Experts Programme - under the coordination of Prof. Dr. Shajulin Benedict.
  • In June 2011, the Telecommunications Industry Association developed a Cloud Computing White Paper, to analyze the integration challenges and opportunities between cloud services and traditional U.S. telecommunications standards.[136]
  • In February 2013, the BonFIRE project launched a multi-site cloud experimentation and testing facility. The facility provides transparent access to cloud resources, with the control and observability necessary to engineer future cloud technologies, in a way that is not restricted, for example, by current business models.[137]

See also

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