Docker with Multiple Mysql Container not working

Question

Docker newbie here.

What I'm trying to achieve is to run multiple MySQL containers with docker compose.

This is my docker-compose.yml:

version: '2'
services:
  mysql:
    build: ./docker-configs/mysql
    ports:
      - "3306:3306"
    environment:
      MYSQL_ROOT_PASSWORD: admin
    volumes:
      - ./data/mysql:/var/lib/mysql
      - ./data/init.d:/docker-entrypoint-initdb.d
  mysql2:
    build: ./docker-configs/mysql2
    ports:
      - "3306:3307"
    environment:
      MYSQL_ROOT_PASSWORD: admin
    volumes:
      - ./data/mysql2:/var/lib/mysql2
      - ./data/init.d:/docker-entrypoint-initdb.d  
  nginx-proxy:
     image: jwilder/nginx-proxy
     volumes:
        - /var/run/docker.sock:/tmp/docker.sock:ro
        - /etc/localtime:/etc/localtime:ro
        - ./docker-configs/nginx-proxy/certs:/etc/nginx/certs
     ports:
        - '80:80'
        - '443:443'

But when I run docker-compose up -d, it shows me the error below:

ERROR: for consultingdocker_mysql2_1 Cannot start service mysql2: driver failed programming external connectivity on endpoint consultingdocker_mysql2_1 (7eac3d28093db7be7b5c81495ee652f6a1df8208388d33df668f1732a118481a): Bind for 0.0.0.0:3306 failed: port is already allocated

ERROR: for mysql2 Cannot start service mysql2: driver failed programming external connectivity on endpoint consultingdocker_mysql2_1 (7eac3d28093db7be7b5c81495ee652f6a1df8208388d33df668f1732a118481a): Bind for 0.0.0.0:3306 failed: port is already allocated ERROR: Encountered errors while bringing up the project.

Please let me know what am I missing here?

Answer 1

The "port" array configuration is inverted. If you write this:

port:
  - "3306:3307"

it means "bind port 3306 on the host network to port 3307 in the container network".

While you want exactly the opposite.

Swap the numbers and it'll work

Answer 2

Port 3306 is already in use on the host by the container mysql , hence you cannot allocate the same port on the host for mysql2 container. Change your mysql2 service config to something as below and it should work -

  mysql2:
    build: ./docker-configs/mysql2
    ports:
      - "3307:3307"
    environment:
      MYSQL_ROOT_PASSWORD: admin
    volumes:
      - ./data/mysql2:/var/lib/mysql2
      - ./data/init.d:/docker-entrypoint-initdb.d  

Now your mysql2 service will be available on port 3307 on the host.