Execute an additional custom Handler

Problem

How do I execute an additional Handler without having to edit a Role (especially for Galaxy Roles)?

Solution

Create an additional Handler with a different name (or even without a name) and add it to your Playbook's Handlers block using listen.

To illustrate this, let's use the Role from Ansible Galaxy geerlingguy.nginx. We want to notify ourselves in a Slack channel if the play notifies restart nginx.

We take a look the available Handlers file in the Role:

geerlingguy.nginx/handlers/main.yml

- name: restart nginx
  ansible.builtin.service:
    name: nginx
    state: restarted

- name: validate nginx configuration
  ansible.builtin.command: nginx -t -c /etc/nginx/nginx.conf
  changed_when: false

- name: reload nginx
  ansible.builtin.service:
    name: nginx
    state: reloaded

And add listen to our Playbook accordingly using the name of the Handler. We could even add more Handlers to it as a list:

- hosts: all
  roles:
    - role: geerlingguy.nginx

  handlers:
    slack:
      channel: "#devops"
      msg: "Nginx was restarted/reloaded on {{ inventory_hostname }}"
      token: "{{ slack_token }}"
    delegate_to: localhost
    listen:
      - restart nginx
      - reload nginx

Explanation

Both Handler names and listen can be called and enables flexible execution of actions decoupled from Handlers in Roles.

Observer Pattern

The listen pattern can also be understood as a simplified Observer Pattern Wikipedia.

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