Exercise 1.5 - Roles: Making your playbooks reusable

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Exercise Description

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.

The "role" feature in Ansible is the way we do this. When you create a role, you deconstruct your playbook into parts and those parts sit in a directory structure. "Wha?? You mean that seemingly useless best practice you mentioned in exercise 1.2?" Yep, that one.

For this exercise, you are going to take the playbook you just wrote and refactor it into a role. In addition, you’ll learn to use Ansible Galaxy.

Let’s begin with understanding how your apache-basic-playbook will break down into a role.

apache-basic-playbook role directory structure

Fortunately, you don’t have to create all of these directories and files by hand. That’s where Ansible Galaxy comes in.

Section 1: Using Ansible Galaxy to initialize a new role

Ansible Galaxy is a free site for finding, downloading, and sharing roles. It’s also pretty handy for creating them, which is what we are about to do here.

Step 1:Navigate to your project

Navigate to your apache-basic-playbook project.

cd ~/apache-basic-playbook

Step 2: Create a directory

Create a directory called roles and cd into it.

mkdir roles
cd roles

Step 3: Initialize new role

Use the ansible-galaxy command to initialize a new role called apache-simple.

ansible-galaxy init apache-simple

Take a look around the structure you just created. It should look a lot like Figure 1 above. However, we need to complete one more step before moving onto Section 2. It is Ansible best practice to clean out role directories and files you won’t be using. For this role, we won’t be using anything from files, tests.

Step 4: Remove directories

Remove the files and tests directories

cd ~/apache-basic-playbook/roles/apache-simple/
rm -rf files tests

Section 2: Breaking your site.yml playbook into the newly created apache-simple role

In this section, we will separate the major parts of your playbook, including vars:, tasks:, template:, and handlers:.

Step 1: Backup

Make a backup copy of site.yml, then create a new site.yml.

cd ~/apache-basic-playbook
mv site.yml site.yml.bkup
vim site.yml

Step 2: Add play definition/Invoke role

Add the play definition and the invocation of a single role.

---
- hosts: web
  name: This is my role-based playbook
  become: yes

  roles:
    - apache-simple

Step 3: Add default variables

Add some default variables to your role in roles/apache-simple/defaults/main.yml.

vim roles/apache-simple/defaults/main.yml

Add the following contents to the file:

apache_test_message: This is a test message
apache_webserver_port: 80

Step 4: Add variables

Add some role-specific variables to your role in roles/apache-simple/vars/main.yml.

vim roles/apache-simple/vars/main.yml

Add the following contents to the file:

httpd_packages:
  - httpd
  - python3-mod_wsgi

Hey, wait just a minute…​did you just have us put variables in two separate places? Yes…​yes we did. Variables can live in quite a few places. Just to name a few:

  • vars directory

  • defaults directory

  • group_vars directory

  • In the playbook under the vars: section

  • In any file which can be specified on the command line using the --extra_vars option

  • On a boat, in a moat, with a goat (disclaimer: this is a complete lie)

Bottom line, you need to read up on variable precedence to understand both where to define variables and which locations take precedence. In this exercise, we are using role defaults to define a couple of variables and these are the most malleable. After that, we defined some variables in /vars which have a higher precedence than defaults and can’t be overridden as a default variable.

Step 5: Create role handler

Create your role handler in roles/apache-simple/handlers/main.yml.

vim roles/apache-simple/handlers/main.yml

Add the following contents to the file:

- name: restart apache service
  service:
    name: httpd
    state: restarted
    enabled: yes

Step 6: Add role tasks

Add tasks to your role in roles/apache-simple/tasks/main.yml.

vim roles/apache-simple/tasks/main.yml

Add the following contents to the file:

- name: install httpd packages
  package:
    name: "{{ item }}"
    state: present
  with_items: "{{ httpd_packages }}"
  notify: restart apache service

- name: create site-enabled directory
  file:
    name: /etc/httpd/conf/sites-enabled
    state: directory

- name: copy httpd.conf
  template:
    src: templates/httpd.conf.j2
    dest: /etc/httpd/conf/httpd.conf
  notify: restart apache service

- name: copy index.html
  template:
    src: templates/index.html.j2
    dest: /var/www/html/index.html

- name: start httpd
  service:
    name: httpd
    state: started
    enabled: yes

Step 7: Download templates

Download a couple of templates into roles/apache-simple/templates/. And then, let’s clean up the templates from exercise 2.1, by removing the old templates directory.

mkdir -p ~/apache-basic-playbook/roles/apache-simple/templates/
cd ~/apache-basic-playbook/roles/apache-simple/templates/
curl -O https://raw.githubusercontent.com/ansible/lightbulb/master/examples/apache-basic-playbook/templates/httpd.conf.j2
curl -O https://raw.githubusercontent.com/ansible/lightbulb/master/examples/apache-basic-playbook/templates/index.html.j2
rm -rf ~/apache-basic-playbook/templates/

Section 3: Running your new role-based playbook

Now that you’ve successfully separated your original playbook into a role, let’s run it and see how it works.

Step 1: Run the playbook

cd ~/apache-basic-playbook
ansible-playbook site.yml

Step 2: Verify your output

If successful, your standard output should look similar to the figure below.

ansible-basic-playbook role-based stdout

Section 4: Review

You should now have a completed playbook, site.yml - with a single role called apache-simple. The advantage of structuring your playbook into roles is that you can now add new roles to the playbook using Ansible Galaxy or simply writing your own. In addition, roles simplify changes to variables, tasks, templates, etc.

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