Q:

Cannot connect to MySQL service in MySQL docker container?

So, I've got a MySQL docker container on which I run a script to write into the database, but when I execute the script, my script throws
mysql.connector.errors.DatabaseError: 2003 (HY000): Can't connect to MySQL server on '127.0.0.1' (111)

Do I have to start the MySQL service in the Dockerfile?
docker-compose.yml:
version: '3.3'

services:
  db:
    build: .
    restart: always
    environment: 
      MYSQL_ROOT_PASSWORD: test
      MYSQL_DATABASE: test
      MYSQL_USER: test
      MYSQL_PASSWORD: test
    volumes: 
      - ./db_data:/docker-entrypoint-initdb.d

A:

First you need to expose the MySQL port 3306 or any other port you set for the MySQL
and then you can get help from commmand parameter.
A working sample would be like this:
version: '3.1'

services:

  db:
    image: mysql
    container_name: mysql_test
    command: --default-authentication-plugin=mysql_native_password
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: root_password
      MYSQL_DATABASE: test
      MYSQL_USER: test_user
      MYSQL_PASSWORD: test_password
    ports:
      - 30001:3306
    expose:
      - 30001
    volumes:
      - my-db:/var/lib/mysql
    networks:
      - test

networks:
  test:

volumes:
  my-db:
    driver: local

With this sample code you will be able to connect with localhost:30001 to your database from host machine and mysql_test:3306 from other containers within the same network.

