I have two services running in Docker containers. When the ports map to the same ports, i.e. 9120:9120 and 9121:9121, then everything works correctly.

However, the containers can not connect to each other when the ports map to different port numbers as shown in this Docker compose file:

  version: "3.9"
  networks:
    service_net:
      name: service_net

  services: 
    base_service:
      build: 
        context: .
        dockerfile: base_service/Dockerfile
      networks: 
        - service_net
      image: base_service
      container_name: base_service
      ports:
        - "19120:9120"
      restart: unless-stopped

    # The second_service uses base_service
    second_service:
      build: 
        context: .
        dockerfile: second_service/Dockerfile
        args:
          BASE_SERVICE_HOST: base_service
          BASE_SERVICE_PORT: 19120
      networks: 
        - service_net
      image: second_service
      container_name: second_service
      ports:
        - "19121:9121"
      restart: unless-stopped

What could be the reason?

CodePudding user response：

The containers them self and other containers in the same network, will see the internal ports.

In this example, all containers running in service_net have access to 9120 and 9121. To fix the problem, change BASE_SERVICE_PORT to 9120 in the Docker compose file.

I fell into this trap and only figured out what was wrong after a debug session. This fact could be described better in docs.docker.com/config/containers/container-networking/ in my opinion.

CodePudding user response：

The numbers in the ports line mean the following:

    ports: 
    - <port-as-known-on-localhost>:<port-as-known-inside-the-docker-compose-network>

If you do this:

    ports:
    - 444:555

Accessing the container from the host where the containers are running on should be done on port 444

Accessing the container from another container inside the compose-network should be done on port 555