fix: Optionally lookup for the latest task definition

[domcleal]

Description

A data lookup for the latest task definition revision to be used in the
ECS service was enabled by default, which continually appeared in
plans/applies.

This is used when the task definition's updated by an external
deployment tool, so this is now disabled and requires enabling the
external_task_definition_updates variable so the default behaviour is
quiet.

Motivation and Context

A fix for #72 as an alternative to #124 which removed the functionality for external deployment tools.

I don't need the external tool support, but I am trying to make the default behaviour quieter and not show this update on every run.

Breaking Changes

Yes, for people using external deployment tools, they should set this new external_task_definition_updates variable to true. This feels like the exception as the default behaviour of the module is to deploy the task definition itself.

How Has This Been Tested?

Two tests, one with the default behaviour (external_task_definition_updates set to false) and verified with a plan that there are no proposed changes/noise:

No changes. Infrastructure is up-to-date.

This means that Terraform did not detect any differences between your
configuration and real physical resources that exist. As a result, no
actions need to be performed.

and again with it set to true shows the previous behaviour:

An execution plan has been generated and is shown below.
Resource actions are indicated with the following symbols:
  ~ update in-place
 <= read (data resources)

Terraform will perform the following actions:

  # module.atlantis.data.aws_ecs_task_definition.atlantis[0] will be read during apply
  # (config refers to values not yet known)
 <= data "aws_ecs_task_definition" "atlantis"  {
      + family          = (known after apply)
      + id              = (known after apply)
      + network_mode    = (known after apply)
      + revision        = (known after apply)
      + status          = (known after apply)
      + task_definition = "atlantis"
      + task_role_arn   = (known after apply)
    }

  # module.atlantis.aws_ecs_service.atlantis will be updated in-place
  ~ resource "aws_ecs_service" "atlantis" {
        cluster                            = "arn:aws:ecs:eu-west-1:...:cluster/atlantis"
        deployment_maximum_percent         = 200
        deployment_minimum_healthy_percent = 50
        desired_count                      = 1
        enable_ecs_managed_tags            = false
        health_check_grace_period_seconds  = 0
        iam_role                           = "aws-service-role"
        id                                 = "arn:aws:ecs:eu-west-1:...:service/atlantis/atlantis"
        launch_type                        = "FARGATE"
        name                               = "atlantis"
        platform_version                   = "LATEST"
        propagate_tags                     = "NONE"
        scheduling_strategy                = "REPLICA"
        tags                               = {
            "Name" = "atlantis"
        }
      ~ task_definition                    = "atlantis:3" -> (known after apply)

        deployment_controller {
            type = "ECS"
        }

        load_balancer {
            container_name   = "atlantis"
            container_port   = 4141
            target_group_arn = "arn:aws:elasticloadbalancing:eu-west-1:...:targetgroup/atlantis/5af07546b36138a7"
        }

        network_configuration {
            assign_public_ip = false
            security_groups  = [
                "sg-063b57edb4bf146f1",
            ]
            subnets          = [
                "subnet-03b28a46d19970c62",
                "subnet-0c1bf5c14d0d97232",
                "subnet-0fa2dd26cbd903e82",
            ]
        }
    }

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

[tomwj]

Nice this looks like an elegant work around given the context.

[parmouraly]

Hi @antonbabenko
Any chance we can get this merged?
Wanted to stop using our fork and this is one of the outstanding issues before we flip back to the using the latest release

[antonbabenko]

Thanks to everyone involved for this improvement.

Fixes #72. Fixes #124.

v2.36.0 has been just released.

[github-actions]

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