I've used Terraform to create a VPC, subnets, ECS instances, routing and a task definition which I am able to run via the AWS console. That gives me a few instances of my small web app running in multiple containers.

I have also been able to create a service using Application Load Balancers in the console but where I fail is when I try to automate that step. I can't attach the container to the target group using Terraform.

From the docs:

resource "aws_alb_target_group_attachment" "test" {
  target_group_arn = "${aws_alb_target_group.test.arn}"
  target_id = "${aws_instance.test.id}"
  port = 80

target_id (Required) The ID of the target. This is the Instance ID for an instance, or the container ID for an ECS container.

I don't know how to specify the container ID for an ECS container. In the console, the page where you register the container in the target group has a drop-down with my container identified as "nancy_template:0:5000".

"nancy_template" or "nancy_template:0:5000" both give me the error:

Error registering targets with target group

Where do I get the 'container ID' the docs say I need to populate the 'target_id' property?

1 Answer 1


I've managed to fix this!

I don't think you need to attach items to the target group yourself, which makes sense because it all happens magically when using the console wizard.

What I did was remove any attempts to attach any targets but define an ALB listener:

resource "aws_alb_listener" "web_front_end" {
  load_balancer_arn = "${aws_alb.nancy_template_alb.id}"
  port              = "80"
  protocol          = "HTTP"

  default_action {
    target_group_arn = "${aws_alb_target_group.web-targetgroup.id}"
    type             = "forward"

and also added this to my service definition:

depends_on = [

..which might not be necessary but ensure that relationship between my target group and load balancer is in place before my service is brought up.

  • aws_ecs_service has a "load_balancer" section that creates the base affiliation. It looks like the listener is to customize that a little more?
    – four43
    Jul 17, 2018 at 19:50
  • This makes sense because the container_id is actually docker's container id, which is only available after the container is run.
    – Isa A
    Aug 31, 2020 at 16:25

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.