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|Original author(s)||Michael DeHaan|
|Developer(s)||Ansible Community / Ansible Inc. / Red Hat Inc.|
|Initial release||February 20, 2012|
188.8.131.52 / September 19, 2017
|Written in||Python, PowerShell|
|Operating system||Linux, Unix-like, Windows|
|Type||Configuration management, Infrastructure as Code, Orchestration engine|
|License||GNU General Public License|
Ansible is software that automates software provisioning, configuration management, and application deployment.
Michael DeHaan, the author of the provisioning server application Cobbler and co-author of the Func framework for remote administration, developed the platform. It is included as part of the Fedora distribution of Linux, owned by Red Hat Inc., and is also available for Red Hat Enterprise Linux, CentOS, and Scientific Linux via Extra Packages for Enterprise Linux (EPEL) as well as for other operating systems.
The name "Ansible" references a fictional instantaneous hyperspace communication system (as featured in Orson Scott Card's Ender's Game (1985), and originally conceived by Ursula K. Le Guin for her novel Rocannon's World (1966)).
As with most configuration management software, Ansible has two types of servers: controlling machines and nodes. First, there is a single controlling machine which is where orchestration begins. Nodes are managed by a controlling machine over SSH. The controlling machine describes the location of nodes through its inventory.
To orchestrate nodes, Ansible deploys modules to nodes over SSH. Modules are temporarily stored in the nodes and communicate with the controlling machine through a JSON protocol over the standard output. When Ansible is not managing nodes, it does not consume resources because no daemons or programs are executing for Ansible in the background.
In contrast with popular configuration management software — such as Chef, Puppet, and CFEngine — Ansible uses an agentless architecture. With an agent-based architecture, nodes must have a locally installed daemon that communicates with a controlling machine. With an agentless architecture, nodes are not required to install and run background daemons to connect with a controlling machine. This type of architecture reduces the overhead on the network by preventing the nodes from polling the controlling machine.
The design goals of Ansible include:
- Minimal in nature. Management systems should not impose additional dependencies on the environment.
- Consistent.[clarification needed]
- Secure. Ansible does not deploy agents to nodes. Only OpenSSH and Python are required on the managed nodes.
- Highly reliable. When carefully written, an Ansible playbook can be idempotent, in order to prevent unexpected side-effects on the managed systems. It should be noted, however, that it is entirely possible to have a poorly written playbook that is not idempotent.
- Low learning curve. Playbooks use an easy and descriptive language based on YAML and Jinja templates.
Modules are considered to be the units of work in Ansible. Each module is mostly standalone and can be written in a standard scripting language (such as Python, Perl, Ruby, Bash, etc.). One of the guiding properties of modules is idempotency, which means that even if an operation is repeated multiple times (e.g., upon recovery from an outage), it will always place the system into the same state.
The Inventory is a description of the nodes that can be accessed by Ansible. By default, the Inventory is described by a configuration file, in INI format, whose default location is in
/etc/ansible/hosts. The configuration file lists either the IP address or hostname of each node that is accessible by Ansible. In addition, nodes can be assigned to groups.
An example inventory:
192.168.6.1 [webservers] foo.example.com bar.example.com
This configuration file specifies three nodes: the first node is specified by an IP address and the latter two nodes are specified by hostnames. Additionally, the latter two nodes are grouped under the
Ansible can also use a custom Dynamic Inventory script, which can dynamically pull data from a different system.
Playbooks express configurations, deployment, and orchestration in Ansible. The Playbook format is YAML. Each Playbook maps a group of hosts to a set of roles. Each role is represented by calls to Ansible tasks.
Ansible Tower is a REST API, web service, and web-based console designed to make Ansible usable for IT teams. It is a hub for automation tasks. Tower is a commercial product supported by Red Hat, Inc. There are intentions by Red Hat, Inc. in releasing Tower as Open Source Software, as announced during AnsibleFest 2016 and documented by available registration web page for updates in this matter.
Ansible Towers was opensourced as AWX in September 2017.
Control machines have to be a Linux/Unix host (for example, Red Hat Enterprise Linux, Debian, CentOS, OS X, BSD, Ubuntu), and Python 2.6 or 2.7 is required (Python 3 support is available as a tech preview since ansible 2.2).
Managed nodes, if they are Unix-like, must have Python 2.4 or later. For managed nodes with Python 2.5 or earlier, the
python-simplejson package is also required. Since version 1.7, Ansible can also manage Windows nodes. In this case, native PowerShell remoting is used, instead of SSH.
Apart from bare metal hosts, ansible can deploy to virtualization and cloud environments, including Amazon Web Services, Atomic, Centurylink, Cloudscale, CloudStack, DigitalOcean, Dimensiondata, Docker, Google Cloud Platform, KVM, Linode, LXC, LXD, Microsoft Azure, OpenStack, OVH, oVirt, Packet, Profitbricks, Pubnub, Rackspace, SmartOS, SoftLayer, Univention, VMware, Webfaction, and XenServer.
- Comparison of open-source configuration management software
- Infrastructure as Code
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