ECS Cluster of a Gateway Service and the Subgraphs Services

I am seeking advice on how to architect a Federated graph within an ECS Cluster.

Does it make sense for the Gateway to communicate to the subgraphs via TCP or another protocol if they are all in the same cluster? If there is an ALB with a listener that directs traffic to a Gateway Fargate service, should the Gateway then communicate with the other Subgraphs Services via TCP?