Ansible Roles and How to Use them in Playbooks

When working with Ansible playbook files https://linuxapt.com/blog/470-create-and-run-ansible-playbook-file, you may have noticed that you could reuse some of the code defined in your existing playbooks. For example, you could re-purpose the code for installing the MariaDB database server on one managed host with different hostnames, users, and passwords for another remote host. This saves a lot of time and energy which would have been used in writing new playbook files from scratch. And this is where the concept of Ansible roles comes in.

An ansible role is a concept of repurposing tasks into individual files which are easier to manage and manipulate. Each role provides a set of tasks, variables, and handlers – to mention a few – that are required for its implementation. Roles allow users to reorganize long and complex playbook structures into simpler, shorter, and neater playbook files. As we mentioned earlier, roles are meant to be reusable, and invoking roles in the playbook file simplifies code & eliminates duplication. Repetitive tasks such as installation, & configuration of applications can be packaged in separate files and reused across various managed hosts.

Here at LinuxAPT, as part of our Server Management Services, we regularly help our Customers to perform related Ansible queries.

In this context, we shall look into how to create and use Ansible roles in playbooks. In between you will learn how to create a role that installs the Apache web server and configures the firewall to open port 80.

How to create an Ansible role ?

We will begin by creating a simple Ansible role. To create a role, simply use the command syntax below where myrole is the name of the role:

$ ansible-galaxy init myrole

For example, to create a role called test_role invoke the command:

$ ansible-galaxy init  test-role

Now, we get that the command spawns a test-role directory and by default, it contains some default directories. You can use the tree command to list them as shown:

$ tree test-role

Below is a brief overview of what each directory contains:

• The 'defaults' folder – This directory holds the default variables that will be required by the role. These variables have the lowest priority and are thus quite easy to override.
• The 'files' folder – This folder comprises files to be copied to the managed or remote host.
• The 'handlers' folder – The directory contains handlers that are usually evoked by the 'notify' directive. You can learn more about Ansible handlers.
• The 'meta' folder – Consists of a role's metadata for instance author, dependencies, etc.
• The 'tasks' folder – It contains a YAML file that defines the list of tasks to be executed by the role itself. It contains the main.yml file.
• The 'templates' folder – The directory comprises template files that can be modified as deemed fit to configure the role.
• The 'tests' folder – Integrates testing with Ansible playbook files.
• The 'vars' folder – Comprises variables that will later be used by the role. role. These variables have a higher priority compared to those in the 'defaults' directory.

Now, We are going to create two roles for demonstration purposes:

The git role – This will install the latest version of Git.

The apache role- This will install the Apache webserver

Create them as follows:

$ sudo ansible-galaxy init git
$ sudo ansible-galaxy init apache

Thereafter, we need to define each role by editing the main.yml file in the 'tasks' folder in each role. Let's start by defining the git role:

$ sudo vim git/tasks/main.yml

Define the task for the git role as shown:

# tasks file for git
#
- name: install git
  apt:
       name: git
       state: present
       update_cache: yes

Then, Save the main.yml file and exit.

Next, define the task for the Apache role:

$ sudo vim apache/tasks/main.yml

Specify the task that installs the Apache webserver:

# tasks file for apache
#
- name: install apache2 webserver
  apt:
       name: apache2
       state: present
       update_cache: yes

In the same way as earlier, save the main.yml file and exit.

How to Create a playbook file and call the roles ?

Once the tasks for each role have been defined in the main.yml file for each role, create a playbook file and reference the roles as shown:

$ sudo vim roles_demo.yml

NOTE:

You need to specify the full path to the role in the playbook:

roles:
      /path/to/role

Here, the roles reside in the same directory as the playbook file, and simply calling them by their names does the trick:

- hosts: localhost
  become: true
  roles:
          - git
          - apache

Then finally, run the playbook file:

$ sudo ansible-playbook /etc/ansible/roles_demo.yml

The roles defined in the playbook file will be referenced and their respective tasks will be executed. Here, Ansible installs both git and Apache webserver.

You can verify the installation by running the commands as shown below:

$ git --version
$ apachectl -v

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