Docker-compose port forwarding - docker

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 any way 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 tries 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.