r/aws_cloudformation_stack: outputs not showing as changed during resource update

[ewbankkit]

Consider this CloudFormation stack:

provider "aws" {}

resource "aws_cloudformation_stack" "test" {
  name = "test"

  template_body = <<STACK
  {
    "AWSTemplateFormatVersion": "2010-09-09",
    "Description": "AWS CloudFormation template that a transformed copy of its input parameter",
    "Parameters": {
      "DataIn": {
        "Type": "String",
        "Description": "Input data"
      }
    },
    "Resources": {
      "NullResource": {
        "Type": "AWS::CloudFormation::WaitConditionHandle"
      }
    },
    "Outputs": {
      "DataOut": {
        "Description": "Output data",
        "Value": {
          "Fn::Join": [
            "",
            [
              "pre-",
              {
                "Ref": "DataIn"
              },
              "-post"
            ]
          ]
        }
      }
    }
}
STACK

  parameters = {
    DataIn = "in1"
  }
}

where outputs depend on parameters.
If the resource is updated by changing parameters (DataIn from "in1" to "in2") then outputs will be updated, however terraform plan does not show that:

% terraform plan

aws_cloudformation_stack.test: Refreshing state... [id=arn:aws:cloudformation:us-west-2:123456789012:stack/test/6381c4a0-2d70-11ee-8daa-026e6b178b5f]

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following
symbols:
  ~ update in-place

Terraform will perform the following actions:

  # aws_cloudformation_stack.test will be updated in-place
  ~ resource "aws_cloudformation_stack" "test" {
        id                 = "arn:aws:cloudformation:us-west-2:123456789012:stack/test/6381c4a0-2d70-11ee-8daa-026e6b178b5f"
        name               = "test"
      ~ parameters         = {
          ~ "DataIn" = "in1" -> "in2"
        }
        tags               = {}
        # (5 unchanged attributes hidden)
    }

Plan: 0 to add, 1 to change, 0 to destroy.

─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

We should expect to see

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following
symbols:
  ~ update in-place

Terraform will perform the following actions:

  # aws_cloudformation_stack.test will be updated in-place
  ~ resource "aws_cloudformation_stack" "test" {
        id                 = "arn:aws:cloudformation:us-west-2:123456789012:stack/test/6381c4a0-2d70-11ee-8daa-026e6b178b5f"
        name               = "test"
      ~ outputs            = {
          - "DataOut" = "pre-in1-post"
        } -> (known after apply)
      ~ parameters         = {
          ~ "DataIn" = "in1" -> "in2"
        }
        tags               = {}
        # (4 unchanged attributes hidden)
    }

Plan: 0 to add, 1 to change, 0 to destroy.

─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

in the plan.

[github-actions]

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[ewbankkit]

Hmm.
If we indiscriminately set outputs to newly computed whenever parameters (or the template) changes then we will cause to falsely show changes, and that's a breaking change.
I'm going to close this one while we think...

[github-actions]

This functionality has been released in v5.13.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.
If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.