Introduction

As you may have seen in my previous article how to use Ansible (https://www.linkedin.com/pulse/configuration-automation-ansible-beginners-lionel-gurret/), we can use many modules to configure and developp our playbooks.

Here are in my opinion the 10 most useful Ansible modules you should know (on Linux environments) !

The Ping Module

The first thing you probably want to do is th check wheter the connection with our host(s) defined in the inventory file is established or not. It does not make sense in playbooks, but it is useful.

Example

# Example from an Ansible Playbook for Linux
- ping:

# Example from an Ansible Playbook for Windows
- win_ping:

It will return “pong” on successful contact.

The Include Module

Use this module when you want to include another playbook or tasks in your current playbook.

Example

- hosts: localhost
  tasks:
    - debug:
        msg: test

- name: Include a play after another play
  include: other_playbook.yaml

The Debug Module

In my opinion the most important module, it will help you to print a state,emton hosts. It will help you to debug your playbooks with its variables or expressions. Specially when you use “when:” statements

Example

- debug:
    msg: "The current value of our variable is : {{ variable_value }}"

The Set_Fact Module

This module allows setting new variables. Variables are set on a host-by-host basis just like facts discovered by the setup module. These variables will be available to subsequent plays during an ansible-playbook run, but will not be saved across executions even if you use a fact cache.

Example

# Example setting simple host fact
- set_fact:
     my_variable: "a value"

The Service Module

Another very useful module, it will help you to manage services on your host(s).

Example

- name: Start service httpd, if not started
  service:
    name: httpd
    state: started

- name: Stop service httpd, if started
  service:
    name: httpd
    state: stopped

- name: Restart service httpd, in all cases
  service:
    name: httpd
    state: restarted

The Shell / Command Modules

We can use the “shell” module when we need to execute a command in remote servers, in the shell of our choice. By default, the commands are run on the /bin/sh shell. You can make use of the various operations like ‘|’,'<‘,’>’ etc. and environment variables like $HOME.

If you don’t need those, you should use the “command” module instead. The command module does not process the commands through a shell. So it doesn’t support the above-mentioned operations.

Example

- name: Executing a Command Using Shell Module 
  shell: ls -lrt > temp.txt

- name: Executing a command using command module
  command: cat hello.txt

The Template / Copy Modules

The Template module is used to copy a configuration file from the local system to the host server. It is the same as the copy module, but it dynamically binds group variables defined by us. So it depends of your need but basically if you need to configure variables in the pushed file, use “template”.

Example

- template:
    src: /mytemplates/foo.j2
    dest: /etc/file.conf
    owner: root
    group: root
    mode: 0644

- name: example copying file with owner and permissions
  copy:
    src: /srv/myfiles/foo.conf
    dest: /etc/foo.conf
    owner: foo
    group: foo
    mode: 0644

The Yum Module

Installs, upgrade, downgrades, removes, and lists packages and groups with the yum package manager.

Example

- name: install the latest version of Apache
  yum:
    name: httpd
    state: latest

- name: upgrade all packages
  yum:
    name: '*'
    state: latest

- name: remove the Apache package
  yum:
    name: httpd
    state: absent

The Lineinfile / Replace Modules

• “Lineinfile” module ensures a particular line is in a file, or replace an existing line using a back-referenced regular expression. This is primarily useful when you want to change a single line in a file only.
• The “replace” module if you want to change multiple, similar lines.

Example

# Replace SELINUX= by SELINUX=enforcing
- lineinfile:
    path: /etc/selinux/config
    regexp: '^SELINUX='
    line: 'SELINUX=enforcing'

# Remove Regexp from file
- lineinfile:
    path: /etc/sudoers
    state: absent
    regexp: '^%wheel'

# Replace Regexp by another line
- replace:
    path: /etc/hosts
    regexp: '(\s+)old\.host\.name(\s+.*)?$'
    replace: '\1new.host.name\2'

The URI Module

Interacts with HTTP and HTTPS web services and supports Digest, Basic and WSSE HTTP authentication mechanisms. So it’s really useful to call API.

Example

- name: Create a JIRA issue
  uri:
    url: https://your.jira.example.com/rest/api/2/issue/
    method: POST
    user: your_username
    password: your_pass
    body: "{{ lookup('file','issue.json') }}"
    force_basic_auth: yes
    status_code: 201
    body_format: json

- name: POST from contents of remote file
  uri:
    url: "https://httpbin.org/post"
    method: POST
    src: /path/to/my/file.json
    remote_src: true