In this chapter, we learned a few important concepts behind Terraform. We now know how Terraform leverages the power of graph theory to manage dependencies between resources and saw how exactly it builds graphs via the terraform graph command. There were many graphs to look at, and with the help of them, we learned how Terraform allows you to add more flexibility to dependency handling via the depends_on and ignore_changes parameters.

After learning about this important backbone of Terraform, we started writing a slightly more mature template and soon figured out that it has some issues with code duplication. Luckily, we managed to use Terraform modules to reduce the duplication and, more importantly, we even found out that the very first template we wrote was already a module.

We even took a first look at variables! But now the question is: how to configure Terraform modules and resources for real? How to supply configuration, where is it stored, and how to manage updates? These are...