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TIL - Terraform refactor resources without recreation

 1 year ago
source link: https://sbulav.github.io/til/terraform/til-terraform-refactor-without-recreation/
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TIL - Terraform refactor resources without recreation

1 minute read

Today I learned that since v1.1, you can move Terraform resources into modules without recreation using moved block. Refactoring doc covers such use cases as renaming resources, enabling count or for_each and splitting module into multiple modules.

But this doc don’t cover my use case, move one or a bunch of resources in the module. For example, you have AWS SQS resources:

resource "aws_sqs_queue" "queue" {
  name                              = var.queue_name
  content_based_deduplication       = var.content_based_deduplication
  deduplication_scope               = var.deduplication_scope
  delay_seconds                     = var.delay_seconds
  fifo_queue                        = var.fifo_queue
  fifo_throughput_limit             = var.fifo_throughput_limit
  kms_data_key_reuse_period_seconds = var.kms_data_key_reuse_period_seconds
  kms_master_key_id                 = var.kms_master_key_id
  max_message_size                  = var.max_message_size
  message_retention_seconds         = var.message_retention_seconds
  policy                            = var.policy
  receive_wait_time_seconds         = var.receive_wait_time_seconds
  redrive_allow_policy              = var.redrive_allow_policy
  redrive_policy                    = var.redrive_policy
  visibility_timeout_seconds        = var.visibility_timeout_seconds
  tags                              = var.tags
}

And you want to refactor it into your module:

module "queue" {
  source                            = "./modules/sqs/"
  content_based_deduplication       = var.content_based_deduplication
  delay_seconds                     = var.delay_seconds
  env_name                          = var.env_name
  fifo_queue                        = var.fifo_queue
  kms_data_key_reuse_period_seconds = var.kms_data_key_reuse_period_seconds
  kms_master_key_id                 = var.kms_master_key_id
  max_message_size                  = var.max_message_size
  message_retention_seconds         = var.message_retention_seconds
  name                              = var.queue_name
  policy                            = var.policy
  product                           = var.product
  queue_name                        = var.queue_name
  receive_wait_time_seconds         = var.receive_wait_time_seconds
  redrive_allow_policy              = var.redrive_allow_policy
  redrive_policy                    = var.redrive_policy
  tags                              = var.tags
  visibility_timeout_seconds        = var.visibility_timeout_seconds
}

By default, aws_sqs_queue.queue will be destroyed and module.queue.aws_sqs_queue.queue will be created. You can override this by using following moved syntax:

moved {
  from = aws_sqs_queue.queue
  to   = module.queue.aws_sqs_queue.queue
}

But if you’ll try to extract module into separate repository, you will get following error:

│ Error: Cross-package move statement
│
│   on main.tf line 41:
│   41: moved {
│
│ This statement declares a move to an object declared in external module package "git::https://github.com/user/modules.git?ref=v0.5.5//modules/sqs".
│ Move statements can be only within a single module package.

According to this ticket Terraform would not have allowed moving into module.x above if the source address of that call had not been a local path.

So here’s my action list to refactor such resources into modules:

  1. Move resources into the local modules folder
  2. Define usage of module in the main block instead of plain resources
  3. Add moved block for every resource, for example: 
    moved {
  from = aws_sqs_queue.queue
  to   = module.queue.aws_sqs_queue.queue
}
  4. Run Terraform plan to make sure that resources aren’t recreated
  5. Apply Terraform plan
  6. Clean up moved blocks

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