Excluded regions field changes order frequently

[enicholson125]

The excluded regions field shows a diff to change the order of the regions, even though the contents of the list hasn't changed. It would be good if the excluded regions field did not consider a change in order to be a change to the resource.

Terraform Version

1.3.5

Affected Resource(s)

• datadog_integration_aws

Terraform Configuration Files

data "aws_region" "current" {}
data "aws_regions" "current" {
  all_regions = true
}

# This code is using the default value of this variable
variable "included_regions" {
  type        = list(string)
  default     = []
}

locals {
  aws_regions_all        = data.aws_regions.current.names
  aws_regions_target   = length(var.included_regions) > 0 ? var.included_regions : [data.aws_region.current.name]
}

resource "datadog_integration_aws" "aws_integration" {
  account_id = local.my_aws_account_id
  role_name  = var.datadog_role_name
  host_tags  = var.host_tags
  # only include specific regions (the Datadog provider only supports excluded regions)  
  excluded_regions                 = setsubtract(local.aws_regions_all, local.aws_regions_target)
  account_specific_namespace_rules = var.account_specific_namespace_rules
}

Expected Behavior

When the excluded regions list does not change, there should be no change in the datadog integration.

Actual Behavior

Sometimes (but not always), we see a flaky diff in the terraform plan to change the order of the regions, e.g.

Terraform will perform the following actions:

  # module.infrastructure.module.kaluza_datadog_integration[0].datadog_integration_aws.aws_integration will be updated in-place
  ~ resource "datadog_integration_aws" "aws_integration" {
      ~ excluded_regions                 = [
          - "us-east-1",
          - "us-east-2",
          - "us-west-1",
          - "us-west-2",
          - "eu-west-1",
          - "eu-central-1",
          - "eu-south-1",
          + "af-south-1",
            "ap-east-1",
          - "ap-southeast-1",
          - "ap-southeast-3",
            "ap-northeast-1",
            # (1 unchanged element hidden)
            "ap-northeast-3",
          - "me-south-1",
          - "me-central-1",
          - "af-south-1",
          - "sa-east-1",
            "ap-south-1",
          + "ap-south-2",
          + "ap-southeast-1",
          + "ap-southeast-3",
            "ca-central-1",
          + "eu-central-1",
          + "eu-central-2",
          + "eu-north-1",
          + "eu-south-1",
          + "eu-south-2",
          + "eu-west-1",
            "eu-west-2",
            "eu-west-3",
          - "eu-north-1",
          + "me-central-1",
          + "me-south-1",
          + "sa-east-1",
          + "us-east-1",
          + "us-east-2",
          + "us-west-1",
          + "us-west-2",
        ]
        id                               = "012345678912:DatadogAWSIntegrationRole"
        # (9 unchanged attributes hidden)
    }

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

Steps to Reproduce

1. terraform plan

This step may be required multiple times, as we do not see this issue every time.

[nkzou]

Unfortunately, Diffs of List types are not well supported with terraform-plugin-sdk. See hashicorp/terraform-plugin-sdk#477, DiffSuppressFunc doesn't support lists. We'll see what we can do about this, possibly migrate to a set or preemptively sorting the list. Hopefully we'll have an update and/or PR up soon.