How do you invoke roles in an Ansible playbook…

Roles in Ansible can be invoked in several ways within a playbook.

Using the roles keyword at the playbook level:

# playbooks/my_playbook.yml
- name: Applying roles to servers
  hosts: webservers
  become: yes
  roles:
    - role: common  # Calling the 'common' role
    - role: nginx   # Calling the 'nginx' role
      vars:         # Passing variables to the role
        nginx_port: 8080
    - another_role # Shortened form of invocation

This method is used for calling roles that will be executed sequentially for all hosts defined in the hosts section.

Using the include_role module in a task list:

# playbooks/my_playbook.yml
- name: Applying roles with conditions
  hosts: appservers
  tasks:
    - name: Include database role (only for dev)
      include_role:
        name: database
      when: env == 'dev' # Calling role with condition

    - name: Include application role
      include_role:
        name: app
      vars:
        app_version: 1.2.0 # Passing variables to the role

The include_role module executes the role as if it were a list of tasks included in the current play. It allows using conditions (when) and loops (loop) to control role execution.

Using the import_role module in a task list:

# playbooks/my_playbook.yml
- name: Import application role
  hosts: appservers
  tasks:
    - name: Import application role for all hosts
      import_role:
        name: app
      vars:
        app_config_file: /etc/app/config.conf # Passing variables

The import_role module is processed at parse time, before actual execution. This means that directives like when will apply to all tasks within the role, not just the role invocation itself. Variables passed via vars will be available inside the role.

The key difference between include_role and import_role lies in processing time: import_role is processed statically at parse time, while include_role is dynamic during playbook execution. This affects the ability to use conditions and loops:

Functionality	`include_role`	`import_role`
Processing	Dynamic	Static
Using `when` to invoke	Yes	No
Using `loop` to invoke	Yes	No
Ability to use variables defined earlier in the play	Yes	No

The choice between methods depends on the required flexibility and processing time. For simple role inclusion, the roles keyword or import_role is usually sufficient. For more complex scenarios with conditions and loops, include_role is used.

How do you invoke roles in an Ansible playbook?