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Comment by oblio | Hacker News Reader

> * ECS: Two containers can not use same port on same node. Anti pattern to containers.

Could you elaborate for this? I'm not sure I understand, are you saying that 2 containers cannot be mapped to the same host port? Because that would seem normal, you can't bind to a port where there's already something listening. But I guess I must be missing something.

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The OP is talking about how when using a classic load balancer in AWS, your containers will be deployed all exposing the same port, kind of like running "docker run -p 5000:5000" on each ec2 in your cluster. Once the port is in use, you can't deploy another of that container on the same ec2 node.

The solution is to use AWS's Application Load Balancers instead, which will allow you dynamically allocate ports for your containers and route traffic into them as ECS Services.

I'm not familiar with the details of AWS here, but maybe the OP means mapping two different host ports to the same port on two different containers? That's all I can imagine that would be a container antipattern in the way described.

That is perfectly possible with ECS, so I don't know what OP was referring to. The thing I remember though is that you have to jump through a lot of hoops like making 4 APIs calls (or worse with pagination) for what should have been a single call to make such a system work on ECS.

Nowaday you would often run containers with a container network(flannel, calico, etc.) that assigns an unique IP per container thus avoids conflicting port mappings regardless how many containers with the same port run on a single host.

Or you have them on a physical private network, each bound to a separate IP, but yes.

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