Introduction to Ansible

Ansible is an open-source software provisioning, configuration management, and application-deployment tool. It runs on many Unix-like systems, and can configure both Unix-like systems as well as Microsoft Windows. It includes its own declarative language to describe system configuration. Ansible was written by Michael DeHaan and acquired by Red Hat in 2015. Ansible is agentless, temporarily connecting remotely via SSH or Windows Remote Management (allowing remote PowerShell execution) to do its tasks.

Unlike most configuration-management software, Ansible does not require a single controlling machine where orchestration begins. Ansible works against multiple systems in your infrastructure by selecting portions of Ansible’s inventory, stored as edit-able, version-able ASCII text files. Not only is this inventory configurable, but you can also use multiple inventory files at the same time and pull inventory from dynamic or cloud sources or different formats (YAML, INI, etc). Any machine with Ansible utilities installed can leverage a set of files/directories to orchestrate other nodes. The absence of a central-server requirement greatly simplifies disaster-recovery planning. Nodes are managed by this controlling machine – typically over SSH. The controlling machine describes the location of nodes through its inventory. Sensitive data can be stored in encrypted files using Ansible Vault since 2014. In contrast with other popular configuration-management software — such as Chef, Puppet, and CFEngine — Ansible uses an agentless architecture, with Ansible software not normally running or even installed on the controlled node. Instead, Ansible orchestrates a node by installing and running modules on the node temporarily via SSH. For the duration of an orchestration task, a process running the module communicates with the controlling machine with a JSON-based protocol via its standard input and output. When Ansible is not managing a node, it does not consume resources on the node because no daemons are executing of software installed.

Design goals:

The design goals of Ansible include:

  • Minimal in nature. Management systems should not impose additional dependencies on the environment.
  • Consistent. With Ansible one should be able to create consistent environments.
  • 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, to prevent unexpected side-effects on the managed systems. It is entirely possible to have a poorly written playbook that is not idempotent.
  • Minimal learning required. Playbooks use an easy and descriptive language based on YAML and Jinja templates.

Modules:

Modules are 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 or YAML 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.

Playbooks:

Playbooks are YAML files that express configurations, deployment, and orchestration in Ansible, and allow Ansible to perform operations on managed nodes. Each Playbook maps a group of hosts to a set of roles. Each role is represented by calls to Ansible tasks.

Ansible Tower:

Ansible Tower is a REST API, web service, and web-based console designed to make Ansible more usable for IT teams with members of different technical proficiencies and skill sets. It is a hub for automation tasks. Tower is a commercial product supported by Red Hat, Inc. but derived from AWX upstream project, which is open source since September 2017.

There is also another open source alternative to Tower, Semaphore, written in Go.

Control machines have to be a Linux/Unix host (for example SUSE Linux Enterprise, Red Hat Enterprise Linux, Debian, CentOS, macOS, BSD, Ubuntu), and Python 2.7 or 3.5 is required.

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 supported by the WS-Management protocol is used, instead of SSH.

The above is a brief about Ansible. Watch this space for more updates on the latest trends in Technology.

 

Leave a Reply

Your email address will not be published. Required fields are marked *