Cycle error when using create_before_destroy with depends_on referencing a module

[lakshmi-gopalakrishnan]

Version

Terraform v0.13.0
+ provider registry.terraform.io/hashicorp/aws v3.4.0
+ provider registry.terraform.io/hashicorp/external v1.2.0
+ provider registry.terraform.io/hashicorp/null v2.1.2

Usecase
We have two modules A and B. A depends on module B. Module A has a create_before_destroy lifecycle policy on it. Module B contains a null resource. The initial creation of the resource using module A goes through fine but any further update runs into cycle error.

This was tested in terraform 0.12.26 and the dependency was specified using module_depends_on variable and there were no issues.

Terraform files

Folder Structure

- moduleA /
     moduleA.tf
- moduleB /
     moduleB.tf
     test.py
- example /
     example.tf

moduleA.tf

module test_package {
    source = "../moduleB"
}

resource "aws_sns_topic" "user_updates" {
  lifecycle {
      create_before_destroy = true
  }
  depends_on = [module.test_package]
  name = "user-updates-topic"
}

moduleB.tf

resource "null_resource" "test_service" {
  triggers = {
        always_run = "${timestamp()}"
    }
  provisioner "local-exec" {
      working_dir = path.module
      interpreter = ["python3"]
      command = "test.py"
  }
}

test.py

def main():
    print("hello world")
    
if __name__ == "__main__":
    main()

example.tf

module "test_module" {
  source      = "../moduleA"
}

Steps to Reproduce
Apply example.tf and it should go through fine. Change the sns topic name in moduleA and run the terraform apply again and it will run into cycle error.

Expected Behaviour
Updates to go through without errors

Actual Behaviour
Error: Cycle: module.test_module.aws_sns_topic.user_updates, module.test_module.aws_sns_topic.user_updates (destroy deposed d55db4bf), module.test_module.module.test_package.null_resource.test_service (destroy deposed 84aabca6), module.test_module.module.test_package (close)

[jbardin]

Hi @laks1206

Thanks for reporting this, and for the example.
I'll also add that since test_service always shows changes in the plan, without any modifications to the user_updates you will get an error in the form of:

provider "X" changed the planned action from
CreateThenDelete to DeleteThenCreate.

This will take a little more investigation to determine if they are related or not.

[ghost]

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