version: '3'
services:

  db:
    image: mysql:5.7
    volumes:
      - db_data:/var/lib/mysql
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_DATABASE: testdatabase
      MYSQL_USER: testdatabase
      MYSQL_PASSWORD: testdatabase12345

  db_ext:
    extends:
      service: db
    volumes:
      - db_data:/var/lib/mysql
    expose:
      - "3306"

volumes:
  db_data: {}