Create module dependencies

expected time	requirements
60 minutes	A computer with Terraform installed.

Goal: Learn how module dependencies work in Terraform.

Explanation

Using modules make the root-module much easier to read, so you’ll likely end up writing and/or using modules.

Modules can depend on each other since Terraform 0.13. (August 2020)

You can simply use depends_on for an explicit dependency or refer to module.NAME.OUTPUT.

Have a look at this experiment

Create a new directory for your expiment.
In that directory, create these directories: network, instance.
In network directory, create a main.tf to create the network.
Make sure the network module outputs the network id.
In the instance directory, create a main.tf to create the instance.
The instance module needs a variable to describe the network this instance should live in.
In instance/main.tf, make sure to use the var.network created in the step above.
Create main.tf in the root-module, calling both the ./network and ./instance module.
Create an implicit dependency from module instance to the module network, by mentioning the module.network.id as input for the instance module.

Are there differences in dependencies on resources and modules?
In the example experiment; The dependency between module one and two is based on a (hidden, not exposed) artefact. How would you rewrite the code to make this dependency visible?

If you need to set an explicit dependency, reconsider if you are doing it wrong.