Previously, we have managed only one resource with Terraform--a single EC2 instance. Obviously, the real infrastructure is much more complicated than a single server. The more resources you have, the more dependencies between them you have to handle. Also, when the number of resources grows, you will have a hard time managing them via a single huge template file.
In this chapter, we will learn about one of the most important features of Terraform: dependency graph. We will figure out how dependencies work and see it in practice by creating a complete virtual network via AWS VPC. Then, we will learn how to work around some limitations in dependency handling using some of the advanced Terraform features. Finally, when we find out that our template is too big, we will use Terraform modules to Don't Repeat Yourself (DRY) our code.
