title: What's the target group port for, when using Application Load Balancer + EC2 Container Service
body: <p>I'm trying to setup an ALB which listens on port 443, load balancing to ECS Docker containers on random ports, lets say I have 2 container instances of the same task definition, listening on port 30000 and 30001.</p>
  
  <p>When I try to create a target group in the AWS EC2 Management console, there's a "port" input field with 1-65535 range.
  What number should I put there?</p>
  
  <p>And when I try to create a new service in the AWS EC2 Container Service console, together with a new target group to connect to a existing ALB, there's no input field for a target group "port".
  After it's created, navigating to the EC2 console, the new target group has port "80".
  Do I have to listen on port 80?
  But the health check happens against the "traffic port", which is the container port, 30000 and 30001, so what's the point?</p>