DevOps Classroom Series – 21/Aug/2020

Reusability in Ansible

• On a Broader note in Ansible we have 3 major ways

  1. Including and importing
  2. Roles
  3. Collections

• Includes vs Imports:

  • They are very similar statements to reuse ansible playbooks but the way ansible handles it is different
    • All import* statements are pre-processed at the time playbook is parsed
    • All include* statements are processed as they are encountered during execution

• Roles:

  • Roles have certain directory structure and they expect files in certain directory names
  • Roles written by community can be searched in Ansible Galaxy

Lets use a role to install mysql

• Role which will be used is this
• Now login into Ansible control Node and execute the following command in new directory

ansible-galaxy install geerlingguy.mysql

• Now go through the documentation and understand how to use the role and the variables
• Now lets create an inventory file

localhost

• Now lets write a playbook which uses the role downloaded

---
- hosts: all
  roles:
    - name: geerlingguy.mysql
      become: yes
  tasks:
    - name: print role execution completed
      debug:
        msg: "mysql role has been executed"

• Now if we execute this ansible will try to install mysql. But how is this stuff working
• To understand that lets write our own role

Ansible role for the tomcat

• Lets create a role in ansible control node

• The default folder structure of role is as shown below

• Now lets understand the importance of folders in roles

  • tasks: All the tasks of your playbook will be placed in this folder. The default file is main.yaml
  • Handlers: All the handlers will have a common location

• Command for creating role is ansible-galaxy init <role-name>

• Once you have created the roles, ansible has some folders where it checks for roles

  1. IN the same folder where playbook.yaml is present, it expects a roles folder and inside roles folder it searches for role names

  installtomcat.yaml
  roles/
    khaja.tomcat/
  

  2. If it doesn’t find it there it navigates to $(home directory)/.ansible/roles/<role-name>

  ~/.ansible/roles/khaja.tomcat/
  

  3. If it doesn’t find here then it searches in /etc/ansible/roles/<role-name>

  /etc/ansible/roles/khaja.tomcat/
  

• The role developed in class is shared @ here

• Even today lots of organization are still using roles.

Ansible Collections

• Collections are distribution format for Ansible that contains
  • playbooks
  • roles
  • modules
  • plugins
• You can install and use collections from ansible-galaxy
• We will be discussing about this in our next session

Block

• In programming world when we have code which can get execptions

try
{
    # some lines of code
}
catch (Exception)
{
    # handling code
}
finally
{
    # cleanup or must call code block
}

• Ansible blocks allow for logical grouping of task in a play for error handling

---
- hosts: all
  become: yes
  tasks:
    - name: install & configure apache
      block:
        - name: install apache
          package:
            name: apache2
          state: present
          when: ansible_os_family == "Debian"
        - name: install php modules
          package:
            name: "{{ item }}"
          loop:
            - php
            - php-mysql
            - php-cli
          when: ansible_os_family == "Debian"
      rescue:
        - name: error occurred
          debug:
            msg: error occurred
      always:
        - name: this executes always
          debug:
            msg: "This always executes"