ECS Service 'Host' Placement Strategy Forcing Service Rebuild

[woodyza]

Small thing: if you use the field host in a placement strategy of type spread within an ECS Service definition a service rebuild will occur on every apply. This looks to be a similar issue to #13216 over in the main repo, except instead of case differences it's an interchangeable term.

host and instanceId are interchangeable and mean the same thing (docs) but it seems the AWS CLI will always return instanceId irrespective of which is originally specified when creating the resource, which I'm picking is the cause of the issue.

Terraform Version

terraform -v
Terraform v0.9.8

Affected Resource(s)

Please list the resources as a list, for example:

• aws_ecs_service

Terraform Configuration Files

resource "aws_ecs_service" "dd_agent_service" {
  name            = "dd-agent"
  cluster         = "${aws_ecs_cluster.api_cluster.id}"
  task_definition = "${aws_ecs_task_definition.dd_agent_task.arn}"
  desired_count   = "1"

  placement_strategy {
    type  = "spread"
    field = "host"
  }
}

Debug Output

Sorry not a debug but the plan output shows enough detail to spot the issue I think:

-/+ aws_ecs_service.dd_agent_service
    cluster:                             "arn:aws:ecs:us-east-1:__REDACTED__:cluster/__REDACTED__" => "arn:aws:ecs:us-east-1:__REDACTED__:cluster/__REDACTED__"
    deployment_maximum_percent:          "200" => "200"
    deployment_minimum_healthy_percent:  "100" => "100"
    desired_count:                       "1" => "1"
    name:                                "dd-agent" => "dd-agent"
    placement_strategy.#:                "1" => "1"
    placement_strategy.1427850681.field: "" => "host" (forces new resource)
    placement_strategy.1427850681.type:  "" => "spread" (forces new resource)
    placement_strategy.3946258308.field: "instanceId" => "" (forces new resource)
    placement_strategy.3946258308.type:  "spread" => "" (forces new resource)
    task_definition:                     "arn:aws:ecs:us-east-1:__REDACTED__:task-definition/dd-agent-task:3" => "arn:aws:ecs:us-east-1:__REDACTED__:task-definition/dd-agent-task:3"

Expected Behavior

No change to the service resource, since there is no change to the placement strategy

Actual Behavior

The service resource will be destroyed and recreated on every terraform apply.

Steps to Reproduce

1. Create an ECS service using a placement strategy spread with field host
2. terraform apply to create
3. terraform apply without changing any tf config will force a new resource

Important Factoids

Perfectly acceptable workaround is to just use instanceId, but I figured it was worth reporting this anyway

References

Are there any other GitHub issues (open or closed) or Pull Requests that should be linked here? For example:

• #13216 in the main repository

[woodyza]

Thanks! 👍

[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!