Ansible (software)

Ansible
Original author(s) Michael DeHaan
Developer(s) Red Hat
Initial release February 20, 2012 (2012-02-20)
Stable release 2.0.2.0 / April 19, 2016 (2016-04-19)
Written in Python
Operating system GNU/Linux, Unix-like, Windows
Type Configuration management, Infrastructure as Code, Orchestration engine
License GNU General Public License
Website www.ansible.com

Ansible, a free-software platform for configuring and managing computers, combines multi-node software deployment, ad hoc task execution, and configuration management.[1] It manages nodes (Linux nodes must have Python 2.4 or later installed on them, Windows nodes require PowerShell 3.0 or later) over SSH or over PowerShell.[2] 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.[3]

Michael DeHaan, the author of the provisioning server application Cobbler and co-author of the Func framework for remote administration, developed the platform.[4] 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.[5] Ansible, Inc commercially supports and sponsors Ansible[6] On 16 October, 2015, Red Hat Inc. announced that it had signed a definitive agreement to acquire Ansible, Inc.[7][8]

The name "Ansible" references the fictional instantaneous hyperspace communication system (featured in Orson Scott Card's Ender's Game,[9] and originally invented by Ursula K. Le Guin for her 1966 novel Rocannon's World).

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.[10] When Ansible is not managing nodes, it does not consume resources because no daemons or programs are executing for Ansible in the background.[11]

In contrast with popular configuration management software — such as Chef, Puppet, and CFEngine — Ansible uses an agentless architecture.[11] 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.[11]

Design goals

The design goals of Ansible[10] 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 (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.[10]

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.[12]

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

Playbooks express configurations, deployment, and orchestration in Ansible.[13] 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.

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.[14] Ansible can manage Windows[15] nodes starting from version 1.7.[14]

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. [10]

Big data integration

Ansible can deploy big data, storage, and analytics environments, including Hadoop, Riak, and Aerospike. In these environments, Ansible helps manage each node's resource consumption, consuming little CPU time and memory in the process. Furthermore, Ansible provides monitoring capabilities that measure such properties as available CPU resources, which can help in the supervision of these nodes.[10]

See also

References

Going Deeper into Ansible Playbooks

External links

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