terraform-provider-aws: DynamoDB TTL Infinitely Out of Sync

DynamoDB tables that have a ttl block with enabled = false will never be able to have their state in sync with the infrastructure.

Terraform Version

Terraform v0.11.3
+ provider.aws v1.9.0
+ provider.template v1.0.0

Affected Resource(s)

• aws_dynamodb_table

Terraform Configuration Files

provider "aws" {
  region = "us-west-2"
}

resource "aws_dynamodb_table" "dynamodb-composite-gsi-composite" {
  count = 1
  name  = "glen-test-ignore"

  read_capacity  = 10
  write_capacity = 10
  hash_key       = "hi"
  range_key      = "me"

  attribute {
    name = "hi"
    type = "S"
  }

  attribute {
    name = "me"
    type = "N"
  }

  attribute {
    name = "x"
    type = "S"
  }

  attribute {
    name = "y"
    type = "N"
  }

  ttl {
    enabled        = false
    attribute_name = ""
  }

  global_secondary_index {
    name            = "glen-test"
    hash_key        = "x"
    range_key       = "y"
    write_capacity  = "10"
    read_capacity   = "10"
    projection_type = "ALL"
  }
}

Debug Output

https://gist.github.com/goakley/c682bf633544bc71cfbe4367df30bfbf

Expected Behavior

Terraform should have determined that no changes needed to be applied, since the DyanmoDB TTL feature is already disabled on the table.

Actual Behavior

Terraform wants to change the TTL to DISABLED, which will end up being a noop. If this is run (and it will succeed), Terraform will determine that the exact same set of changes will need to be made on the next Terraform run. That is, it will never think that the DynamoDB TTL feature is disabled even though it is.

Steps to Reproduce

Please list the steps required to reproduce the issue, for example:

1. terraform apply
2. terraform apply

Important Factoids

This example is a simplified version of our production code, which references variables to set the enabled property of the ttl block. Many of our tables don’t use TTL, so enabled is set to false, but this causes Terraform to forever think that the DynamoDB table is out of sync with the Terraform state.

References

None.