In Ansible, a handler is similar to a regular task in a playbook, 

but it will only run if a task alerts the handler. 

Handlers are automatically loaded by roles/<role_name>/handlers/main.yaml. 

Handlers will run once, after all of the tasks are completed in a particular play.

Handlers are like special tasks which only run 

if the Task contains a “notify” directive. 

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1tasks:

2  - name: install nginx

3    apt: pkg=nginx state=installed update_cache=true

4    notify:

5     - start nginx

6 handlers:

7   - name: start nginx

8     service: name=nginx state=started

In the above example 

after installing NGINX we are starting the server using a `start nginx` handler.

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