How to Move a Terraform Resource Into a Module Using Moved Block

Starting from v1.1, Terraform provides a powerful feature known as the moved block. This feature allows you to reorganize your Terraform configuration without causing Terraform to perceive the refactor as a deletion and creation of resources.

In this article, we will walk through a few examples of Terraform refactoring using the moved block.

Prerequisites

• Terraform (>=1.1)

Move a Resource Into Module

First, we will create a sample S3 bucket to reference as a standalone resource. In your Terraform configuration directory, create a new ./lab-demo/s3.tf file.

resource "aws_s3_bucket" "moved_demo" {
  bucket = "moved-demo"
  tags = {
    env = "lab"
  }
}

Now, let’s create a module directory ./modules/aws/s3 and move the ./lab-demo/s3.tf into ./modules/aws/. The directory structure should look like this:

├── lab-demo
│   ├── main.tf
│   ├── s3.tf # Moved to ./modules/aws/s3/s3.tf
│   ├── modules
│       └── aws
│           └── s3
│               └── s3.tf

Since we have the resource in the module, we need to update the reference in the ./lab-demo/main.tf file.

module "s3" {
  source = "./modules/aws/s3"
}

If we run terraform init && terraform plan now, Terraform will propose to destroy and recreate the same S3 bucket. This is because Terraform thinks that the object reference does not exist anymore.

  # aws_s3_bucket.moved_demo will be destroyed
  # (because aws_s3_bucket.moved_demo is not in configuration)
  ...
  ...
   # module.s3.aws_s3_bucket.moved_demo will be created

To fix this, we need to add a moved block to the ./lab-demo/main.tf file.

module "s3" {
  source = "./modules/aws/s3"
}

moved {
  from = aws_s3_bucket.moved_demo
  to   = module.s3.aws_s3_bucket.moved_demo
}

If you do the terraform plan again, Terraform will recognize the move and not propose to destroy and recreate the resource.

  # aws_s3_bucket.moved_demo has moved to module.s3.aws_s3_bucket.moved_demo
    resource "aws_s3_bucket" "moved_demo" {
        id                          = "moved-demo"
        tags                        = {
            "env" = "lab"
        }
    }
Plan: 0 to add, 0 to change, 0 to destroy.

Once you apply the configuration, you can remove the moved block from the ./lab-demo/main.tf file.

Moving Resource Between Modules

The moved block can also be used to move resources between modules. Let’s create a new module ./modules/aws/another_module and move the ./modules/aws/s3/s3.tf into ./modules/aws/another_module. The directory structure should look like this:

├── lab-demo
│   ├── main.tf
│   ├── modules
│       └── aws
│           ├── s3
│           └── another_module
│               └── s3.tf # Moved from ./modules/aws/s3/s3.tf

Since we have the resource in the module, we need to update the reference in the ./lab-demo/main.tf file.

module "s3" {
  source = "./modules/aws/another_module"
}

In order to move the resource from s3 module another_module , we can use the same moved block to the ./lab-demo/main.tf file.

module "s3" {
  source = "./modules/aws/s3"
}

moved {
  from = module.s3.aws_s3_bucket.moved_demo
  to   = module.another_module.aws_s3_bucket.moved_demo
}

And the terraform plan will show the resource move.

  # module.s3.aws_s3_bucket.moved_demo has moved to module.another_module.aws_s3_bucket.moved_demo
    resource "aws_s3_bucket" "b" {
        id                          = "moved-demo"
        tags                        = {
            "env" = "lab"
        }
    }
Plan: 0 to add, 0 to change, 0 to destroy.

Renaming a Module

Similarly, we can also rename the module using the moved block. Let’s rename the another_module to s3 and move the resource back to the s3 module. Below is an example main.tf file.

## Before: main.tf

module "s3" {
  source = "./modules/aws/s3"
}

## After: main.tf

module "s3_renamed_module" {
  source = "./modules/aws/s3"
}

moved {
  from = module.s3
  to   = module.s3_renamed_module
}

In this case, all the resources in the s3 module will be moved to the s3_renamed_module module.

Resources :

https://developer.hashicorp.com/terraform/language/v1.1.x/modules/develop/refactoring