Ansible

Requirements

Requirements on hosts:

• SSH
• Python 2.5 or later

Control machine requires Python 2.6 or later.

Ansible is push-based, i.e. updates occur only when a playbook is run. However, pull-based support is available via ansible-pull.

No abstraction is available, so playbooks are OS and distribution specific (e.g. use apt for Debian).

Ansible runs each task in parallel across every host, and does not move on to the next task until all hosts have completed.

Configuration file

Ansible will look for an ansible.cfg file in the following locations:

1. Location specified by ANSIBLE_CONFIG configuration.
2. ./ansible.cfg
3. ~/.ansible.cfg
4. /etc/ansible/ansible.cfg

Placing the file in the current directory alongside playbooks is the easiest solution, and keeps everything together.

Sample configuration file:

[defaults]
hostfile = hosts
remote_user = vagrant
private_key_file = ~/.vagrant.d/insecure_private_key
host_key_checking = False

Command module

Arbitrary commands can be executed using the command module:

ansible hostname -m command -a uptime

Passing -s runs the command as root, using sudo.

Update packages:

ansible hostname -s -m apt -a "update_cache=yes"

Install package:

ansible hostname -s -m apt -a "name=apache2"

Restarting service:

ansible hostname -s -m service -a "name=apache2 state=restarted"

Playbooks

Playbooks are YAML files which contain tasks to be run on a group of hosts. Each playbook must contain:

• A list of hosts.
• A list of tasks to be run on the hosts.

Command: ansible-playbook playbook.yml

The sudo option in a playbook means that every task should be run via sudo. This is particularly useful on Ubuntu servers, and also on servers where root SSH login has been disabled.

Handlers

Handlers are similar to tasks, but they only run if notified. An example handler might be:

handlers:
    - name: restart apache
      service:
        name: apache2
        state: restarted

This will run if a task includes:

notify: restart apache

Handlers run after all tasks, and only run once regardless of how many times they are notified.

File conventions

• Support files (e.g. configuration) in: files
• Template files in: templates