Ansible Variables

Variables could be defined in #202204272036 and #202204272043. However, it is recommended to put variables, primarily credentials that are essential for connection such as username and password, into Inventory.

Note: Variables stored in #202204300820 are called facts.

To access a variable or fact in Playbook, use the filter syntax or Jinja syntax {{ variable }}. The variable could be stored as YAML file inside directories named host_vars or group_vars for the Playbook to access. The variables for hosts will take precedence over variables for groups since they are more specific.

Control Flow

For conditionals, we could use the #202204300820 when. One can use comparison operators such as ==, !=, >, >=, < and <=, or in keyword to check whether the value is found in a list. It has some limitation for potential large amount of tasks. For this, it is advised to use handler or separate the tasks into a #202204272036 and then included later. The usage is shown as below:

...
  tasks:
  - name: Install apache
    apt:
      name: apache2
      state: latest
    when: ansible_distribution == 'Debian' or
          ansible_distribution == 'Ubuntu'
...

register module could be used in order to store the return status of a task in order to be used in a later stage. A better approach in control flow could be by using handlers. The following shows the example use case:

...
  tasks:
  - name: Ensure httpd package is present
    yum:
      name: httpd
      state: latest
    register: httpd_results
  
  - name: Restart httpd
    service:
      name: httpd
      state: restart
    when: httpd_results.changed
...

Module notify is used to notify the handlers when there is a change of state of the task. Use the module handlers to define handler. Its format is quite similar to #the tasks module. For example:

...
  tasks:
  - name: Ensure httpd package is present
    yum:
      name: httpd
      state: latest
    notify: restart_httpd
  
  handlers:
  - name: restart_httpd
    service:
      name: httpd
      state: restart
...

We could loop over a list of variables or items using the module loop. This could become handy when there is a task should be repeated with multiple variables. That being said, using loop is unfavourable due to the performance hit. A lot of times, #202204300820 has better built-in than loop. The following code shows how to use loop:

...
  tasks:
  - name: Ensure user is present
    user:
      name: "{{ item }}"
      state: present
    loop:
      - dev_user
      - qa_user
      - prod_user
...

Note: item can store an object, meaning it could be a JSON list instead of just value.