I have a docker compose file which is setup up so that each container can have access to 2 networks (frontend or backend) such that

services:
  frontend:
    image: whatever:latest
    networks:
      - front

  backend:
    image: whatever:latest
    ports:
      - "7233:7233"
    networks:
      - back

  middle:
    image: whatever:latest
    networks:
      - back
      - front

networks:
  front:
    driver: bridge
  back:
    driver: bridge

I have set up a tcmdump inside the container on port 7233 and can see packets coming in if I hit the port from another container.

However if I try and hit the port from outside – from the host – then I see no packets.

My understanding is this :

If you have 2 networks then the container will have 2 virtual ethernet adapters.
The port mapping in docker compose will bind the port as LISTEN on ALL available adapters.

I have tcpdumped on both adapters and only 1 is receiving packets, and then only if the traffic originates from within the container network, i.e. from another container.

How can I get the external route to work as well?