Integrate terraform plan with cloudformation changesets

[hashibot]

This issue was originally opened by @torfredrik as hashicorp/terraform#6014. It was migrated here as part of the provider split. The original body of the issue is below.

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When a cloudformation stack is changed in terraform the terraform plan only shows a change to the stack, it would be useful to know the underlying resource changes that will occur. An easy way to add this feature is using cloudformation change sets .

[nathanielks]

@apparentlymart I'm debating on if this is a problem to tackle now and could use your input. In thinking through how to create an aws_cloudformation_changeset resource, I believe an issue that still wouldn't be solved is displaying what changes would actually be applied to the stack. If I understand what you were saying in the previous ticket as well as hashicorp/terraform#8769, presenting the changes that CloudFormation would be applying to the stack would be an issue because Terraform doesn't support custom diff presentation. Is that correct?

To further clarify: in creating a aws_cloudformation_changeset resource, whenever changes were to be made, only the changes to the actual resource would be displayed (eg, parameter_a being changed from true to false), not that an EC2 Instance would be created or not. Does Terraform currently support the ability to customize the diff presentation? Or maybe this could be solved by using an aws_cloudformation_changeset resource in conjunction with a data source, and the data source could display the diff?

resource "aws_cloudformation_changeset" "main" {
  name_prefix  = "some-stack"
  description  = "Performs updates on some-stack CloudFormation Stack"
  stack_name   = "some-stack"
  capabilities = ["CAPABILITY_IAM"]

  parameters = {
    foo = "bar"
    bar = "baz"
    baz = true
  }

  tags = {
    "foo" = "bar"
  }

  template_body = "${file(var.template_path)}"
}

data "aws_cloudformation_changeset" "main" {
  id = "${aws_cloudformation_changeset.main.id}"
}

Or maybe this could be solved by using an external data source and a script?

[lorengordon]

This might also help with a problem when the CloudFormation template contains a transform, since the transform must be executed through a changeset. Right now, if you attempt to launch a stack using the aws_cloudformation_stack resource the API will return an error:

* aws_cloudformation_stack.foo: Creating CloudFormation stack failed: ValidationError: CreateStack cannot be used with templates containing Transforms.    status code: 400, request id: <elided>

[github-actions]

Marking this issue as stale due to inactivity. This helps our maintainers find and focus on the active issues. If this issue receives no comments in the next 30 days it will automatically be closed. Maintainers can also remove the stale label.

If this issue was automatically closed and you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thank you!

[lorengordon]

Wait, can we reopen this please!

[fdiorazio]

This actually would be a great feature since changesets are very fast compared to deleting the entire stack and re-deploying it.

[ghost]

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 feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!