Exposing to public more than 1 port with AWS ECS service and Elastic LoadBalancer

You don't need any workaround, AWS ECS now supports multiple target groups within the same ECS service. This will be helpful for the use-cases where you wanted to expose multiple ports of the containers.

Currently, if you want to create a service specifying multiple target groups, you must create the service using the Amazon ECS API, SDK, AWS CLI, or an AWS CloudFormation template. After the service is created, you can view the service and the target groups registered to it with the AWS Management Console.

For example, A Jenkins container might expose port 8080 for the Jenkins web interface and port 50000 for the API.

Ref:

https://docs.aws.amazon.com/AmazonECS/latest/developerguide/register-multiple-targetgroups.html

https://aws.amazon.com/about-aws/whats-new/2019/07/amazon-ecs-services-now-support-multiple-load-balancer-target-groups/

Update: I was able to configure target group using Terraform but did not find so far this option on AWS console.

resource "aws_ecs_service" "multiple_target_example" {
  name            = "multiple_target_example1"
  cluster         = "${aws_ecs_cluster.main.id}"
  task_definition = "${aws_ecs_task_definition.with_lb_changes.arn}"
  desired_count   = 1
  iam_role        = "${aws_iam_role.ecs_service.name}"

  load_balancer {
    target_group_arn = "${aws_lb_target_group.target2.id}"
    container_name   = "ghost"
    container_port   = "3000"
  }

  load_balancer {
    target_group_arn = "${aws_lb_target_group.target2.id}"
    container_name   = "ghost"
    container_port   = "3001"
  }

  depends_on = [
    "aws_iam_role_policy.ecs_service",
  ]
}

Version note: Multiple load_balancer configuration block support was added in Terraform AWS Provider version 2.22.0.

ecs_service_terraform

I can't say that this will be a nice workaround but I was working on a project where I need to run Ejabberd using AWS ECS but the same issue happened when its come to bind port of the service to the load balancer.

I was working with terraform and due to this limitation of AWS ECS, we agree to run one container per instance to resolve the port issue as we were supposed to expose two port.

If you do not want to assign a dynamic port to your container and you want to run one container per instance then the solution will definitely work.

1. Create a target group and specify the second port of the container.

2. Go to the AutoScalingGroups of your ECS cluster

3. Edit and add the newly created target group of in the Autoscaling group of the ECS cluster

So if you scale to two containers it's mean there will be two instances so the newly launch instance will register to the second target group and Autoscaling group take care of it. This approach working fine in my case, but few things need to be consider.

Do not bind the primary port in target, better to bind primary port in ALB service. The main advantage of this approach will be that if your container failed to respond to AWS health check the container will be restart automatically. As the target groupe health check will not recreate your container.

This approach will not work when there is dynamic port expose in Docker container.

AWS should update its ECS agent to handle such scenario.

I have faced this issue while creating more than one container per instances and second container was not coming up because it was using the same port defined in the taskdefinition.

What we did was, Created an Application Load balancer on top of these containers and removed hardcoded ports. What application load balancer does when it doesn't get predefined ports under it is, Use the functionality of dynamic port mapping. Containers will come up on random ports and reside in one target group and the load balancer will automatically send the request to these ports.

More details can be found here