What's the target group port for, when using Application Load Balancer + EC2 Container Service

Question

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

Answer 1

The port in the target group is used in conjunction with auto-scaling groups and if you ever plan to use those you want to use the right port from the start. Why? Because you can not change it after the target group has been created and auto-scaling will simply not work if you set the port wrong.