Ansible Handlers

Ansible Handlers

This contains a handlers file named ‘main.yml’. I sure wish they had named all these YAML files after their purpose instead of ‘main’, it would have made it easier when using an editor with multiple panes or tabs, and easier to find the file by name.

Handlers are tasks that are only run if triggered by a ‘notify’ directive on another task. This is typically used to restart a service only if configuration files has changed.

Using a handler

- name: Configure Wingnuts 
  template: src=wingnuts.config.j2 dest=/etc/wingnuts
  handler: restart wingnuts

This will log an event to call the handler ‘restart wingnuts’. Ansible is smart. It will only run the task for the handler once, after all the tasks that trigger this event have completed.

Declaring a handler

In the ‘handlers/main.yml’ file, you declare a handler exactly as you wold define a task.

---
# Handlers for Wingnut

- name: restart wingnut
  service: name=wingnut state=restarted

The name matches the name given in the ‘handler’ declaration of the task, and Ansible does the rest.

Caveats

Handlers should avoid using includes, because of known issues with run-time evaluation causing the handler not to be seen.

It might not be wise to have a handler that has a ‘handler’, aside from the risk of recursion. If you need to have nested dependencies, things have already become too complex and gotten out of hand. Frankly, this might not even be legal syntax.