Terraform: Up & Running, 2nd Edition

Chapter 3. How to Manage Terraform State

In Chapter 2, as you were using Terraform to create and update resources, you might have noticed that every time you ran terraform plan or terraform apply, Terraform was able to find the resources it created previously and update them accordingly. But how did Terraform know which resources it was supposed to manage? You could have all sorts of infrastructure in your AWS account, deployed through a variety of mechanisms (some manually, some via Terraform, some via the CLI), so how does Terraform know which infrastructure it’s responsible for?

In this chapter, you’re going to see how Terraform tracks the state of your infrastructure and the impact that has on file layout, isolation, and locking in a Terraform project. Here are the key topics I’ll go over:

• What is Terraform state?

• Shared storage for state files

• Limitations with Terraform’s backends

• Isolating state files

  • Isolation via workspaces

  • Isolation via file layout

• The terraform_remote_state data source

Example Code

As a reminder, you can find all of the code examples in the book at: https://github.com/brikis98/terraform-up-and-running-code.

What Is Terraform State?

Every time you run Terraform, it records information about what infrastructure it created in a Terraform state file. By default, when you run Terraform in the folder /foo/bar, Terraform creates the file /foo/bar/terraform.tfstate. This file contains a custom JSON format that records a mapping from the Terraform ...