Handlers-Ansible

In Ansible, handlers are special tasks that run only when notified by other tasks. They are typically used for operations that need to occur after a change has been made, such as restarting a service after its configuration file has been modified.

Defining and Using Handlers

1. Define a Handler: Handlers are defined in a playbook similar to regular tasks but are listed under the handlers section. Each handler has a unique name that other tasks can use to reference it.

handlers:
  - name: restart apache
    service:
      name: httpd
      state: restarted        

Notify a Handler: Tasks that can trigger handlers include a notify directive, specifying which handlers to trigger when the task reports a changed status.

tasks:
  - name: copy the httpd configuration file
    copy:
      src: /path/to/httpd.conf
      dest: /etc/httpd/conf/httpd.conf
    notify: restart apache        

Example Playbook with Handlers

Here's a complete example demonstrating the use of handlers in a playbook:

---
- hosts: webservers
  become: yes

  tasks:
    - name: install httpd
      yum:
        name: httpd
        state: present

    - name: copy the httpd configuration file
      copy:
        src: /path/to/httpd.conf
        dest: /etc/httpd/conf/httpd.conf
      notify: restart apache

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

  handlers:
    - name: restart apache
      service:
        name: httpd
        state: restarted        

Key Points

1. Handlers Only Run When Notified: Handlers are only executed if they are notified by a task that has changed something. If no tasks notify the handler, it will not run.
2. Handlers Run Once per Playbook: Even if multiple tasks notify the same handler, it will only run once at the end of the play. This ensures that operations such as service restarts are performed efficiently.
3. Notification Names Must Match: The name specified in the notify directive must exactly match the name of the handler.
4. Handlers Are Run in the Order of Notification: If multiple handlers are notified, they will run in the order they were defined.

Thank You for reading.