How to Fix \"OperationalError: Can\'t connect to MySQL server\" When Using Django and Docker?

Connecting Django to MySQL in Docker

When attempting to connect Django to MySQL in a Docker environment using Compose, you may encounter an "OperationalError: Can't connect to MySQL server" issue. This error typically arises due to incorrect container configurations or database settings.

Resolving the Issue

The correct parameters to establish a connection between Django and MySQL in Docker are:

• Set 'HOST': 'db' in Django's settings.py file.
• Use 3306 as the port number in settings.py.
• Set the MYSQL_PORT environment variable to 3306 in docker-compose.yml.
• Keep the MYSQL_HOST environment variable as localhost.

To ensure that you're connected successfully, you can use the following command in your docker-compose.yml file:

  web:
    image: onlybelter/django_py35
    command: /bin/sh -c "python check_db.py --service-name mysql --ip db --port 3306"
    volumes:
      - .:/djcode

This command runs a script that checks if the MySQL port is open. If it is, the script will display a message indicating success.

Additional Tips

• To connect to the MySQL container directly, use mysql -h 127.0.0.1 -P 3302 -u root -p in your shell.
• If you have multiple Django containers running, make sure to use different port numbers for each one to avoid conflicts.
• You can use Docker's docker-compose logs command to check for any potential errors or warnings related to database connectivity.

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