Original author(s) | Development status Active | |
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Developer(s) Ansible Community / Ansible Inc. / Red Hat Inc. Initial release February 20, 2012; 5 years ago (2012-02-20) Stable release 2.2.1.0 / January 16, 2017; 39 days ago (2017-01-16) Repository github.com/ansible/ansible | ||
Ansible is an open-source automation engine that automates cloud provisioning, configuration management, and application deployment. Once installed on a control node, Ansible, which is an agentless architecture, connects to a managed node through the default OpenSSH connection type.
Contents
- Architecture
- Design goals
- Modules
- Inventory configuration
- Playbooks
- Ansible Tower
- Platform support
- Cloud integration
- References
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.
Ansible, Inc. (originally AnsibleWorks, Inc.) was the company set up to commercially support and sponsor Ansible. Red Hat acquired Ansible in October 2015.
The name "Ansible" references a fictional instantaneous hyperspace communication system (as featured in Orson Scott Card's Ender's Game (1985), and originally invented by Ursula K. Le Guin for her novel Rocannon's World (1966)).
Architecture
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.
Design goals
The design goals of Ansible include:
Modules
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.
Inventory configuration
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.comThis 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
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.
Ansible Tower
Ansible Tower is an 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. One may register for updates in releasing Tower as Open Source Software.
Written in Go, semaphore is an Open Source alternative to Tower.
Platform support
Control machines must have Python 2.6 or 2.7. Operating systems supported on control machines include most Linux and Unix distributions, such as Red Hat, Debian, CentOS, OS X, BSD, and Ubuntu, among others.
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.
Cloud integration
Ansible can deploy to virtualization environments and public and private cloud environments, including Amazon Web Services, CloudStack, DigitalOcean, Eucalyptus Cloud, Google Cloud Platform, KVM, Microsoft Azure, OpenStack, Rackspace, SoftLayer, VMware, and XenServer.