Terraform Refactoring Made Easy with Moved Blocks

Ever embarked on a Terraform refactoring project, only to be met with the prospect of destroying and recreating resources? Fear not, infrastructure enthusiasts! The moved block is here to streamline your workflow and ensure a smooth upgrade process.

What are Moved Blocks?

A moved block is a powerful Terraform configuration element that tracks the history of resource renames and movements within your code. This proves invaluable when refactoring your infrastructure code, as it allows you to avoid unnecessary destruction and recreation of existing resources.

Putting Moved Blocks into Action: A Renaming Example

Imagine you have a Terraform module that defines an AWS instance named aws_instance.a. However, you later decide to give it a more descriptive name, aws_instance.b. Here's how the moved block simplifies this process:

1. Update your module configuration to include a new resource named
3. with the desired configuration.
4. Add a moved block specifying the previous and new names:

resource "aws_instance" "a" {
  count = 2  # (resource-type-specific configuration)
}

resource "aws_instance" "b" {
  count = 2  # (resource-type-specific configuration)
}

moved {
  from = aws_instance.a
  to   = aws_instance.b
}
        

In this example, the moved block informs Terraform that any existing resources previously named aws_instance.a should now be considered instances of aws_instance.b. By understanding this historical context, Terraform avoids unnecessary actions during the next terraform apply.

Benefits of Using Moved Blocks

• Seamless Refactoring: Refactor your code with confidence, knowing that existing resources won't be destroyed and recreated.
• Clearer Code History: moved blocks act as a log of resource changes, improving code maintainability for future developers.
• Smoother Upgrades: Ensure a seamless upgrade experience for your users by avoiding disruptions caused by resource recreation.

By embracing the moved block, you can make your Terraform code more resilient, adaptable, and easier to maintain in the long run. So, the next time you tackle a refactoring project, remember this valuable tool and keep your infrastructure upgrades smooth sailing!

Neeraj Pandey