Docker-compose port forwarding

Question

I have a website hosted on shared hosting on production. The website connects to the database via localhost in the code. In my docker-compose I have a php:5.6-apache and mysql:5.6 instance.

Is there anyway to tell docker-compose to have port 3306 on the web container port forwarded to 3306 on the db container so that when the web container ties to connect to localhost on 3306 it gets sent to db on 3306 and also share port 80 on the web container to the outside world?

Current docker-compose.yml:

version: "3"

services:
  web:
    build:  .
    #image: php:5.6-apache
    ports:
     - "8080:80"
    environment:
     - "APP_LOG=php://stderr"
     - "LOG_LEVEL=debug"
    volumes:
     - .:/var/www/html
    network_mode: service:db # See https://stackoverflow.com/a/45458460/95195
#    networks:
#     - internal
    working_dir: /var/www
  db:
    image: mysql:5.6
    ports:
     - "3306:3306"
    environment:
      - "MYSQL_XXXXX=*****"
    volumes:
      - ./provision/mysql/docker-entrypoint-initdb.d:/docker-entrypoint-initdb.d
#    networks:
#     - internal

networks:
  internal:
    driver: bridge

Current error:

ERROR: for web Cannot create container for service web: conflicting options: port publishing and the container type network mode

Answer 1

Yes it is possible. You need to use the network_mode option. See the below example

version: '2'

services:
  db:
    image: mysql
    environment:
      MYSQL_ROOT_PASSWORD: root
    ports:
      - "80:80"
      - "3306:3306"
  app:
    image: ubuntu:16.04
    command: bash -c "apt update && apt install -y telnet && sleep 10 && telnet localhost 3306"
    network_mode: service:db

outputs

app_1  | Trying 127.0.0.1...
app_1  | Connected to localhost.
app_1  | Escape character is '^]'.
app_1  | Connection closed by foreign host.

network_mode: service:db instructs docker to not assign the app services it own private network. Instead let it join the network of db service. So any port mapping that you need to do, needs to happen on the db service itself.

The way I usually use it is different, I create a base service which runs a infinite loop and the db and app service both are launched on base service network. All ports mapping need to happen at the base service.