Adding count to terraform module

Question

I have already deployed my VPC via this module listed below before I added a count.

This worked just fine, however do to changes in our infrastructure, I need to add a count to the module

module "core_vpc" {
  source = "./modules/vpc"

  count          = var.environment == "qa" || var.environment == "production" ? 1 : 0
  aws_region     = var.aws_region
  environment    = var.environment
  system         = var.system
  role           = var.system
  vpc_name       = var.system
  vpc_cidr       = var.vpc_cidr
  ssh_key_name   = var.ssh_key_name
  ssh_key_public = var.ssh_key_public
  nat_subnets    = var.nat_subnets
  nat_azs        = var.vpc_subnet_azs

}

Now Terraform wants to update my state file and destroy much of my configuration and replace it with what is shown in the example below. This is of course not just limited to route association, but all resources created within the module.I can't let this happen as I have production running and not want to mess with that.

 module.K8_subnets.aws_route_table_association.subnet[0] will be destroyed

and replace it with:

module.K8_subnets[0].aws_route_table_association.subnet[0] will be created

Is there a way of preventing Terraform of making these changes? Short of changing it manually in the tf-state. All I want is the for the VPC not to be deployed in DEV.

Thanks.

Church

You can try a terraform state mv 'module.K8_subnets' 'module.K8_subnets[0]' - but make sure to backup your state files prior to that. – Remainderman

Cool, I will give that a try. – Church

So that worked really well. Thanks @luk2302! You rock! – Church

@Remainderman - could you consider turning that into an answer so you can increase your vast reputation points? Your answer was very timely and helped me out as well. – Asexual

Answer 1

You can "move" the terraform state using tf state mv src target. Specifically you can move the old non-counter version into the new counted version at index 0:

terraform state mv 'module.K8_subnets' 'module.K8_subnets[0]'

This works for individual resources as well as for entire modules. And it works for for_each resource as well, there you would not have an index but a key to move to. And this even works the other way around, if you remove the count / for_each but want to still keep the resource(s).

Remainderman

this is really inconvenient when you change a module that is used in many places, and you have to run this command for each occurance of the module. – Badly

@Badly yes, that is why terraform not too long ago introduced a moved { } block: terraform.io/language/modules/develop/refactoring – Remainderman

Answer 2

More suitable answer is the one in comments of accepted answer.

Terraform has introduced a moved { } block from Terraform v1.1 and later.

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

Remonstrant