What's the target group port for, when using Application Load Balancer + EC2 Container Service
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.
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?
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?
Answer
Turns out, when combined with ECS, the target group's port doesn't mean anything. You don't need to listen on that port.