|Initial release||February 20, 2012|
|Stable release||220.127.116.11 / 26 March 2015|
|Operating system||GNU/Linux, Unix-like, Windows|
|Type||Configuration management, Orchestration engine|
|License||GNU General Public License|
Ansible is a free software platform for configuring and managing computers. It combines multi-node software deployment, ad hoc task execution, and configuration management. It manages nodes over SSH or PowerShell and requires Python (2.4 or later)  to be installed on them. Modules work over JSON and standard output and can be written in any programming language. The system uses YAML to express reusable descriptions of systems.
The platform was created by Michael DeHaan, the author of the provisioning server application Cobbler and co-author of the Func framework for remote administration. 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 other operating systems. Ansible is commercially supported and sponsored by Ansible, Inc.
It was named "Ansible" after the fictional instantaneous hyperspace communication system featured in Orson Scott Card's Ender's Game, and originally invented by Ursula K. Le Guin for her 1966 novel Rocannon's World.
As with most configuration management software, Ansible distinguishes 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 vulnerable agents to nodes. Only OpenSSH is required, which is already critically tested.
- Highly reliable. The idempotent resource model is applied to deployment to prevent side-effects from re-running scripts.
- Low learning curve. Playbooks use an easy and descriptive language based on YAML.
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 (examples include: 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 (i.e.; 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 configuration file:
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
webservers group name.
Ansible can also be pointed towards a custom "Dynamic Inventory" script, which can pull data from any different software 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 call tasks.
Managed nodes must have Python 2.4 or later. For managed nodes with Python 2.5 or earlier, the
python-simplejson package is also required. Ansible can manage Windows nodes starting from version 1.7.
Ansible can deploy to virtualization environments and public and private cloud environments, including VMware, OpenStack, AWS, Rackspace Cloud Servers, DigitalOcean Droplets, Eucalyptus Cloud, KVM, and CloudStack.
Big data integration
Ansible can deploy big data, storage and analytics environments, including Hadoop, Riak, and Aerospike. The problem addressed by Ansible in these environments includes the management of resource consumption of each node. Specifically, big data, storage, and analytics environments intend to be resource efficient by wasting as little CPU time and memory as possible. Furthermore, Ansible provides monitoring capabilities that measure quantities such as CPU resources available which can help in the supervision of these nodes.
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