Private "host" for docker compose network

Question

Given a docker-compose file something like this

version: "3.8"
services:
  service-one:
    ports:
      - "8881:8080"
    image: service-one:latest
  service-one:
    ports:
      - "8882:8080"
    image: service-two:latest

what happens is that service-one is exposed to the host network on port 8881 and service-two would be exposed on the host network at port 8882.

What I'd like to be able to arrange is that in the network created for the docker-compose there be a "private host" on which service-one will be exposed at port 8881 and service-two will be exposed on port 8882 such that any container in the docker-compose network will be able to connect to the "private host" and connect to the services on their configured HOST_PORT but not on the actual docker host. That is, to have whatever network configuration that usually bridges from the CONTAINER_PORT to the HOST_PORT happen privately within the docker-compose network without having the opportunity for there to be port conflicts on the actual host network.

If you do nothing, `service-one` can reach the host name `service-two` on its "normal" port 8080. (You can delete the `ports:`, even.) Would that meet your needs? — David Maze, Jun 15 '20 at 20:57
@DavidMaze, thanks for your reply. I'm aware of this. I'm trying to avoid having to change the containers to expect the other services on different hosts. — Victor, Jun 15 '20 at 22:01

score 1 · Accepted Answer · answered Jul 08 '20 at 13:16

I tweak this to fit to your case. The idea is to run socat in a gateway so that containers nor images changed (just service names). So, from service-X-backend you are able to connect to:

service-one on port 8881, and
service-two on port 8882

Tested with nginx containers.

If you wish to make some ports public, you need to publish them from the gateway itself.

version: "3.8"

services:

  service-one-backend:
    image: service-one:latest
    networks:
      - gw

  service-two-backend:
    image: service-two:latest
    networks:
      - gw

  gateway:
    image: debian
    networks:
      gw:
        aliases:
          - service-one
          - service-two
    depends_on:
      - service-one-backend
      - service-two-backend
    command: sh -c "apt-get update
                 && apt-get install -y socat
                 && nohup bash -c \"socat TCP-LISTEN: 8881,fork TCP:service-one-backend:8080 2>&1 &\"
                 && socat TCP-LISTEN: 8882,fork TCP:service-two-backend:8080"


networks:
  gw:

Thank you. I was hoping there was some way to do this with docker networking but in lieu of that I think this is a good option. — Victor, Jul 10 '20 at 17:11

Private "host" for docker compose network

1 Answers1