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- In this video,

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we are going to explore
the use of handlers.

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So what is a handler?

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A handler is a task that is only executed

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when it is triggered by a task

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that has changed something.

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Handlers are executed
after all tasks in a play.

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So that's important to realize,

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and you need to organize the contents

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of your playbook accordingly.

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And if any task fails after the task

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that has called the handler,

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the handler is not executed at all.

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If you don't like that,

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you need to use force handlers
to change that behavior.

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Let's go check out an example.

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So let's have a look at an example.

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The example is in handlers.yml.

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So what are we doing?

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We are running the
playbook on the host rocky.

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We install httpd,

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then we copy over an index html file.

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That's a file that should
exist in tmp index html.

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And this is the important
part about the handler,

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we use notify restart web.

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Restart web actually needs to correspond

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to the name of the handler.

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And that is the case as
you can see right here.

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So name it restart web.

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And then that's the interesting thing,

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I included the task that is going to fail.

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We will have a failure on purpose.

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That's exactly what I want to demonstrate.

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So I want to demonstrate

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that the handler is not going to run,

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if any of the tasks that is triggered

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after the handler is going to fail.

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So let's run it and figure
out what's going to happen.

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Ansible playbook and handlers.yml.

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So here we can see copy index
html has changed something.

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So it should trigger the handle normally,

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but after this handle triggering task,

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another task is failing.

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And the default behavior

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in Ansible happens to be if execution

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of a specific task, on a
specific host, is failing.

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Then further play execution
on that host is aborted.

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And for that reason, we
don't see the handler.

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Now, if you want to change that behavior

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that is pretty easy.

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You need to get back in the handler's code

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and you need to use force handlers:yes

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or true or whatever.

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It's a boolean,

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so you can go whatever way you want.

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Ansible is pretty flexible,

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regarding the way how
you write your boolean.

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So let's run it again.

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And here we can see that...

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Oh boy, nothing is happening.

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Why isn't anything happening?

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I'll take a second to think about it.

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Did you think about it?

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Have a look at the task copy index html

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which hasn't changed anything.

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And this is the mere
essence of using handlers.

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Handlers are going to be operational

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if something has changed.

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So the index html already existed.

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And that means that I need

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to use an ad hoc command
Ansible all minus m file

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minus a name is /var/www/html/index.html

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and state is absent.

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And then I'm going to run it again

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and then we will see
what is going to happen.

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So now we can see that yeah,

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index html is changing something.

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Copy nothing is still failing,

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but the handler has restarted web.

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And that is what I wanted you to see here.

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Force handlers allows
you to force the handlers

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to be started,

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even if any subsequent tasks are failing.

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And that's all.