Exercise 1.7 - Roles: Making your playbooks reusable

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While it is possible to write a playbook in one file as we’ve done throughout this workshop, eventually you’ll want to reuse files and start to organize things.

Ansible Roles are the way we do this. When you create a role, you deconstruct your playbook into parts and those parts sit in a directory structure. This is explained in more detail in the best practice already mentioned in exercise 3.

Step 7.1 - Understanding the Ansible Role Structure

Roles are basically automation built around include directives and really don’t contain much additional magic beyond some improvements to search path handling for referenced files.

Roles follow a defined directory structure; a role is named by the top level directory. Some of the subdirectories contain YAML files, named main.yml. The files and templates subdirectories can contain objects referenced by the YAML files.

An example project structure could look like this, the name of the role would be “apache”:

apache/
├── defaults
│   └── main.yml
├── files
├── handlers
│   └── main.yml
├── meta
│   └── main.yml
├── README.md
├── tasks
│   └── main.yml
├── templates
├── tests
│   ├── inventory
│   └── test.yml
└── vars
    └── main.yml

The various main.yml files contain content depending on their location in the directory structure shown above. For instance, vars/main.yml references variables, handlers/main.yaml describes handlers, and so on. Note that in contrast to playbooks, the main.yml files only contain the specific content and not additional playbook information like hosts, become or other keywords.

Tip

There are actually two directories for variables: vars and default: Default variables have the lowest precedence and usually contain default values set by the role authors and are often used when it is intended that their values will be overridden.. Variables can be set in either vars/main.yml or defaults/main.yml, but not in both places.

Using roles in a Playbook is straight forward:

---
- name: launch roles
  hosts: web
  roles:
    - role1
    - role2

For each role, the tasks, handlers and variables of that role will be included in the Playbook, in that order. Any copy, script, template, or include tasks in the role can reference the relevant files, templates, or tasks without absolute or relative path names. Ansible will look for them in the role’s files, templates, or tasks respectively, based on their use.

Step 7.2 - Create a Basic Role Directory Structure

Ansible looks for roles in a subdirectory called roles in the project directory. This can be overridden in the Ansible configuration. Each role has its own directory. To ease creation of a new role the tool ansible-galaxy can be used.

Tip

Ansible Galaxy is your hub for finding, reusing and sharing the best Ansible content. ansible-galaxy helps to interact with Ansible Galaxy. For now we’ll just using it as a helper to build the directory structure.

Okay, lets start to build a role. We’ll build a role that installs and configures Apache to serve a virtual host. Run these commands in your ~/ansible-files directory:

[student<X>@ansible ansible-files]$ mkdir roles
[student<X>@ansible ansible-files]$ ansible-galaxy init --offline roles/apache_vhost

Have a look at the role directories and their content:

[student<X>@ansible ansible-files]$ tree roles

Step 7.3 - Create the Tasks File

The main.yml file in the tasks subdirectory of the role should do the following:

• Make sure httpd is installed

• Make sure httpd is started and enabled

• Put HTML content into the Apache document root

• Install the template provided to configure the vhost

WARNING

The main.yml (and other files possibly included by main.yml) can only contain tasks, not complete Playbooks!

Change into the roles/apache_vhost directory. Edit the tasks/main.yml file:

---
- name: install httpd
  yum:
    name: httpd
    state: latest

- name: start and enable httpd service
  service:
    name: httpd
    state: started
    enabled: true

Note that here just tasks were added. The details of a playbook are not present.

The tasks added so far do:

• Install the httpd package using the yum module

• Use the service module to enable and start httpd

Next we add two more tasks to ensure a vhost directory structure and copy html content:

- name: ensure vhost directory is present
  file:
    path: "/var/www/vhosts/{{ ansible_hostname }}"
    state: directory

- name: deliver html content
  copy:
    src: index.html
    dest: "/var/www/vhosts/{{ ansible_hostname }}"

Note that the vhost directory is created/ensured using the file module.

The last task we add uses the template module to create the vhost configuration file from a j2-template:

- name: template vhost file
  template:
    src: vhost.conf.j2
    dest: /etc/httpd/conf.d/vhost.conf
    owner: root
    group: root
    mode: 0644
  notify:
    - restart_httpd

Note it is using a handler to restart httpd after an configuration update.

The full tasks/main.yml file is:

---
- name: install httpd
  yum:
    name: httpd
    state: latest

- name: start and enable httpd service
  service:
    name: httpd
    state: started
    enabled: true

- name: ensure vhost directory is present
  file:
    path: "/var/www/vhosts/{{ ansible_hostname }}"
    state: directory

- name: deliver html content
  copy:
    src: index.html
    dest: "/var/www/vhosts/{{ ansible_hostname }}"

- name: template vhost file
  template:
    src: vhost.conf.j2
    dest: /etc/httpd/conf.d/vhost.conf
    owner: root
    group: root
    mode: 0644
  notify:
    - restart_httpd

Step 7.4 - Create the handler

Create the handler in the file handlers/main.yml to restart httpd when notified by the template task:

---
# handlers file for roles/apache_vhost
- name: restart_httpd
  service:
    name: httpd
    state: restarted

Step 7.5 - Create the index.html and vhost configuration file template

Create the HTML content that will be served by the webserver.

• Create an index.html file in the “src” directory of the role, files:

[student<X>@ansible ansible-files]$ echo 'simple vhost index' > ~/ansible-files/roles/apache_vhost/files/index.html

• Create the vhost.conf.j2 template file in the role’s templates subdirectory.

# {{ ansible_managed }}

<VirtualHost *:8080>
    ServerAdmin webmaster@{{ ansible_fqdn }}
    ServerName {{ ansible_fqdn }}
    ErrorLog logs/{{ ansible_hostname }}-error.log
    CustomLog logs/{{ ansible_hostname }}-common.log common
    DocumentRoot /var/www/vhosts/{{ ansible_hostname }}/

    <Directory /var/www/vhosts/{{ ansible_hostname }}/>
  Options +Indexes +FollowSymlinks +Includes
  Order allow,deny
  Allow from all
    </Directory>
</VirtualHost>

Step 7.6 - Test the role

You are ready to test the role against node2. But since a role cannot be assigned to a node directly, first create a playbook which connects the role and the host. Create the file test_apache_role.yml in the directory ~/ansible-files:

---
- name: use apache_vhost role playbook
  hosts: node2
  become: yes

  pre_tasks:
    - debug:
        msg: 'Beginning web server configuration.'

  roles:
    - apache_vhost

  post_tasks:
    - debug:
        msg: 'Web server has been configured.'

Note the pre_tasks and post_tasks keywords. Normally, the tasks of roles execute before the tasks of a playbook. To control order of execution pre_tasks are performed before any roles are applied. The post_tasks are performed after all the roles have completed. Here we just use them to better highlight when the actual role is executed.

Now you are ready to run your playbook:

[student<X>@ansible ansible-files]$ ansible-playbook test_apache_role.yml

Run a curl command against node2 to confirm that the role worked:

[student<X>@ansible ansible-files]$ curl -s http://22.33.44.55:8080
simple vhost index

All looking good? Congratulations! You have successfully completed the Ansible Engine Workshop Exercises!

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