Introduction

Modules (also referred to as “task plugins” or “library plugins”) are the ones that do the actual work in ansible, they are what gets executed in each playbook task. But you can also run a single one using the ‘ansible’ command.

Let’s review how we execute three different modules from the command line:

ansible webservers -m service -a "name=httpd state=started"
ansible webservers -m ping
ansible webservers -m command -a "/sbin/reboot -t now"

Each module supports taking arguments. Nearly all modules take key=value arguments, space delimited. Some modules take no arguments, and the command/shell modules simply take the string of the command you want to run.

From playbooks, Ansible modules are executed in a very similar way:

- name: reboot the servers
  action: command /sbin/reboot -t now

Which can be abbreviated to:

- name: reboot the servers
  command: /sbin/reboot -t now

Another way to pass arguments to a module is using yaml syntax also called ‘complex args’

- name: restart webserver
  service:
    name: httpd
    state: restarted

All modules technically return JSON format data, though if you are using the command line or playbooks, you don’t really need to know much about that. If you’re writing your own module, you care, and this means you do not have to write modules in any particular language – you get to choose.

Modules should be idempotent, and should avoid making any changes if they detect that the current state matches the desired final state. When using Ansible playbooks, these modules can trigger ‘change events’ in the form of notifying ‘handlers’ to run additional tasks.

Documentation for each module can be accessed from the command line with the ansible-doc tool:

ansible-doc yum

A list of all installed modules is also available:

ansible-doc -l