Mysql Question posted in
The official MySQL documentation can be found here.

"Can't connect to MySQL server on 'mysql' ([Errno 111] Connection refused)", but can be started manually

I’m trying to run Docker + Flask + MySQL, and here is my docker-compose.yaml:


services:
  dockerflaskexample:
    image: dockerflaskexample
    build:
      context: .
      dockerfile: ./Dockerfile
    ports:
      - 5002:5002
    volumes:
      - app_code:/app
    depends_on:
      - mysql
    container_name: dockerflaskexample
  mysql:
    image: mysql:latest
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: webapp-db-root-password
      MYSQL_DATABASE: webapp-db
      MYSQL_USER: webapp-db-user
      MYSQL_PASSWORD: webapp-db-password
    volumes:
      - mysql_data:/var/lib/mysql
    ports:
      - "3306:3306"
volumes:
  mysql_data:
  app_code:

… and in __init__.py:

# Establishing a connection to the MySQL database
connection = pymysql.connect(
    host='mysql',
    database='webapp-db',
    user='webapp-db-user',
    password='webapp-db-password',
    port=3306,
    charset='utf8mb4',  # adjust charset if necessary
)

After I compose up, container dockerflaskexample always fails with the following error:

2024-04-02 16:25:05 pymysql.err.OperationalError: (2003, "Can't connect to MySQL server on 'mysql' ([Errno 111] Connection refused)")

However, if I simply run the Exited (3) container again, it works.

May I know why is it so? Is it because mysql isn’t ready when the webapp started?

Tags:

2

Answers


  1. 0

    Your intuition is correct(you need to wait for the database to start). You can wait either using Docker Compose or using Python.

    Although it’s waiting for a rabbitMQ service, the Docker Compose solution is stated here. You need a different healthcheck for the mysql service configuration:

        healthcheck:
      test: ["CMD", "mysqladmin", "ping", "-h", "localhost"]
      interval: 5s
      timeout: 10s
      retries: 3

    If you prefer to use Python, you can easily create the retry logic as described here.

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  2. 0

    It seems issue due to networks. You are trying to use host as the container_name this requires adding both containers to the same network. The network can be defined at the bottom of the .yml file (It can be external as well).

    Please check the example.

    services:
  dockerflaskexample:
    ...
    networks:
      - service-network
  mysql:
    ...
    networks:
      - service-network

...

networks:
  service-network:
    name: service-network

    also check – https://docs.docker.com/compose/networking/#specify-custom-networks

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