WEBVTT

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In this lecture, we will learn how
to link two resources together

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by making use
of resource attributes.

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In the last few lectures,
we saw how to use variables

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to improve the
reusability of our code.

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Right now, we have two resources
in our configuration file.

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Each of this resource has a set
of arguments that are used

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to create that resource.

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For the file resource,

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we have used the filename
and content as the arguments.

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For the pet resource,
we have used the prefix,

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separator and length.

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When this configuration
is applied,

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Terraform creates a file
and a random_pet resource.

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The name of the random_pet is
displayed on the screen as an ID,

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which is Mr. Bull in this case.

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As it stands, there is no dependency
between these two resources,

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but this rarely ever happens

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in a real world infrastructure
provisioning process.

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There are bound to be multiple
resources that are dependent

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on each other.

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What if we want to make use of
the output of one resource

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and use it as an input
for another one?

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What if we want the content
of the file to use the name

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generated by the
random_pet resource?

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Currently, the content
of the file is set to

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"My favorite pet is Mr. Cat".

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What if we want it to be set to
the name that is generated

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by the random_pet resource?

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To understand this, let us jump
back to the documentation

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for the random_pet resource
in registry.terraform.io.

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You would have noticed that
there are plenty of examples

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which are provided
in the documentation,

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including examples
for the arguments,

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but there is also a section
called attribute reference,

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which provides the list of
attributes returned back

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from the resource after you
run a Terraform apply.

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In this case, the random_pet
resource returns just one attribute

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called ID, which is of type string.

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The ID is the pet name generated
after we run Terraform apply

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as we have seen before.

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Our goal is to make use of the
attribute called ID and to make use

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of it as the content
of the local file resource.

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For this, we can make use
of an expression like this.

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This expression is used to
reference the attribute

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from the resource called my-pet.

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The syntax for using this
reference expression is resource type

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followed by the resource
name and the attribute to be used,

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all of which are separated
by a period or a dot.

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The resource type in this
example is random_pet.

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This is followed by my-pet,
which is the resource name

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and the attribute used is ID.

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You would have also noticed that
we are making use of the dollar symbol

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followed by the expression

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which is enclosed
within curly braces.

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This is known as an
interpolation sequence.

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Since the content argument
already uses a string type data,

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this sequence is used to
evaluate the expression given

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between the curly braces,
convert the result to a string,

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and then insert it to the
final string, like this.

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Now, let us apply the changes
made and allow Terraform

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to recreate the local file.

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In the output, you can see that
the content is being replaced

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to our desired value, and it
contains the name of the pet

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that was generated by
the random_pet resource.

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That's it for this lecture.

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Now, let's head over
to the hands-on labs

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and explore working with
reference expressions

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and resource attributes in Terraform.