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- Now that we've talked
about the fail module,

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we should also briefly
cover the assert module.

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So the assert module is
a module that you can use

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to show a message on success
as well as on failure.

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It's a bit like the fail module

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but it has more advanced options.

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Let me show you.

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So the first playbook I want
to show you is assert size

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but the wrong version of it.

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I made it easy to recognize
which one is working,

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which one is not, because sometimes I like

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including playbooks that aren't doing

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what you expect them to do.

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So what this is doing,
this is using VARs prompt,

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I'm going into local host
because there is no reason

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to actually go out to another host.

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And then the playbook is
checking if file size is valid

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and in order to do so using
assert, so assert that.

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And then you can list
a number of conditions.

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Condition number one, file
size smaller than 100.

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This is an integer, right?

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It's not between quotes,

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then we have file size greater than one.

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We do a fail message file size must be

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and we do a success message.

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In case of failure, it will abort,

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in case of success, it will continue.

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And if it continues, it
creates a file with this size.

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Notice that it's using
bytes instead of megabytes,

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who cares about the actual size.

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But what matters is the assertion.

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So let's run it, ansible-playbook
on assertsize-wrong,

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and let's give it 50.

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That should be okay.

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And what are we getting?

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Oh, that is interesting, we are getting

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the conditional check file
size smaller than 100 failed.

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The error was unexpected templating error

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and not supported between
instances of string and integer.

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Now what is the thing?

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The thing is that if you enter
a value using VARs prompt,

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we get a string.

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If you want to do greater
than smaller than operations

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on a variable, it needs to be an integer.

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And that is not the case here,
the variable type is wrong

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and that is why we need to
do something in addition.

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So let me show you the
contents of assert size

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so that we can investigate
what is different in there.

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Now what do we see?

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We see that the variable is defined

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but the variable is defined by int,

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this is passing through
the integer filter.

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So this will make sure
that the file size variable

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is interpreted as an integer.

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Notice that this filter is not changing

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the contents of the variable,

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it's just changing the interpretation.

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And we do the same for the other file size

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and now we can try again and
that should be more successful.

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And we also include this private, no,

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no need to hide the actual results.

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So there we go, I'm going for the 50.

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And in the 50 we see file size is good,

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let's continue, create a
file and change localhost

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and now I'm going for
5,000 which will be wrong

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and there you go, the
assertion is having it fail.

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So that is what is
really nice about assert.

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Assert, a little bit like
block and rescue and always

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is just another way of
implementing something

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that looks like an if then else statement.

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And you're going to need
them in Ansible as well

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and that is what makes assert really cool.