EFS volume bind auto detaching/reattaching on every `terraform apply` for ECS task definition

Question

I am currently using AWS ECS for my service deployment. For the shared volumes, I am binding some EFS volumes.

Here is my task definition:

resource "aws_ecs_task_definition" "ecs-fargate" {
  family                   = var.ecs_task_definition_name
  container_definitions    = var.container_definitions
  requires_compatibilities = ["FARGATE"]
  network_mode             = "awsvpc"
  cpu                      = var.ecs_task_cpu
  memory                   = var.ecs_task_memory
  execution_role_arn       = var.ecs_task_execution_role_arn
  task_role_arn            = var.ecs_task_role_arn

  dynamic "volume" {
    for_each = var.volumes
    content {
      name = volume.value["name"]
      efs_volume_configuration {
        file_system_id     = volume.value["file_system_id"]
      }
    }
  }
}

var "volumes" {
default = [
    {
      name           = "vol1"
      file_system_id = "fs-xxxxxxxx"
    },
    {
      name           = "vol2"
      file_system_id = "fs-xxxxxxxx"
    }
  ]
}

The Terraform code above is working fine as well.

But when I do the terraform apply every time, the task definition detaches the EFS volume first and re-attach the same again. Here is the screenshot of the issue:

     - volume {
          - name = "vol1" -> null

          - efs_volume_configuration {
              - file_system_id          = "fs-xxxxxxx" -> null
              - root_directory          = "/" -> null
            }
        }
      + volume {
          + name = "vol1"

          + efs_volume_configuration {
              + file_system_id     = "fs-xxxxxx"
              + root_directory     = "/"
            }
        }

Am I missing some additional Terraform configuration here for the above issue?

Answer 1

If you apply your TF config you should see that no changes are actually performed. If you check TF docs for efs_volume_configuration you will see that it has number of attributes. Some of them will be default, such as your root_directory which you don't specify. TF may need to pick up those default values after your initial apply. Thus later you may seem them in your subsequent terraform plan.