Django (containerized) cannot connect to MySQL (containerized) on local machine

Question

I set up a MySQL database using the official image from DockerHub by the command on a virtual machine with CentOS 7.6

docker run -d -p 3306:3306 --name mysql -v /opt/mysql/mysql-data/:/var/lib/mysql -e MYSQL_DATABASE=myblog -e MYSQL_ROOT_PASSWORD=123456 mysql:5.7

Then I built and started a Django project in another container named myblog with the settings

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'myblog',
        'USER': os.environ.get("MYSQL_USER", 'root'),
        'PASSWORD': os.environ.get("MYSQL_PASSWD", '123456'),
        'HOST': os.environ.get("MYSQL_HOST", '127.0.0.1'),
        'PORT': os.environ.get("MYSQL_PORT", '3306')
    }
}

However, when I opened the interactive bash shell of the Django project and tried to makemigrations with the command python3 manage.py makemigrations , Django complains about the connection with the following exception:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/pymysql/connections.py", line 583, in connect
    **kwargs)
  File "/usr/lib64/python3.6/socket.py", line 724, in create_connection
    raise err
  File "/usr/lib64/python3.6/socket.py", line 713, in create_connection
    sock.connect(sa)
ConnectionRefusedError: [Errno 111] Connection refused

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/django/db/backends/base/base.py", line 216, in ensure_connection
    self.connect()
  File "/usr/local/lib/python3.6/site-packages/django/db/backends/base/base.py", line 194, in connect
    self.connection = self.get_new_connection(conn_params)
  File "/usr/local/lib/python3.6/site-packages/django/db/backends/mysql/base.py", line 227, in get_new_connection
    return Database.connect(**conn_params)
  File "/usr/local/lib/python3.6/site-packages/pymysql/__init__.py", line 94, in Connect
    return Connection(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/pymysql/connections.py", line 325, in __init__
    self.connect()
  File "/usr/local/lib/python3.6/site-packages/pymysql/connections.py", line 630, in connect
    raise exc
pymysql.err.OperationalError: (2003, "Can't connect to MySQL server on '127.0.0.1' ([Errno 111] Connection refused)")

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "manage.py", line 22, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python3.6/site-packages/django/core/management/__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python3.6/site-packages/django/core/management/__init__.py", line 375, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python3.6/site-packages/django/core/management/base.py", line 316, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/local/lib/python3.6/site-packages/django/core/management/base.py", line 353, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python3.6/site-packages/django/core/management/base.py", line 83, in wrapped
    res = handle_func(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/django/core/management/commands/makemigrations.py", line 103, in handle
    loader.check_consistent_history(connection)
  File "/usr/local/lib/python3.6/site-packages/django/db/migrations/loader.py", line 281, in check_consistent_history
    applied = recorder.applied_migrations()
  File "/usr/local/lib/python3.6/site-packages/django/db/migrations/recorder.py", line 61, in applied_migrations
    if self.has_table():
  File "/usr/local/lib/python3.6/site-packages/django/db/migrations/recorder.py", line 44, in has_table
    return self.Migration._meta.db_table in self.connection.introspection.table_names(self.connection.cursor())
  File "/usr/local/lib/python3.6/site-packages/django/db/backends/base/base.py", line 255, in cursor
    return self._cursor()
  File "/usr/local/lib/python3.6/site-packages/django/db/backends/base/base.py", line 232, in _cursor
    self.ensure_connection()
  File "/usr/local/lib/python3.6/site-packages/django/db/backends/base/base.py", line 216, in ensure_connection
    self.connect()
  File "/usr/local/lib/python3.6/site-packages/django/db/utils.py", line 89, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/usr/local/lib/python3.6/site-packages/django/db/backends/base/base.py", line 216, in ensure_connection
    self.connect()
  File "/usr/local/lib/python3.6/site-packages/django/db/backends/base/base.py", line 194, in connect
    self.connection = self.get_new_connection(conn_params)
  File "/usr/local/lib/python3.6/site-packages/django/db/backends/mysql/base.py", line 227, in get_new_connection
    return Database.connect(**conn_params)
  File "/usr/local/lib/python3.6/site-packages/pymysql/__init__.py", line 94, in Connect
    return Connection(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/pymysql/connections.py", line 325, in __init__
    self.connect()
  File "/usr/local/lib/python3.6/site-packages/pymysql/connections.py", line 630, in connect
    raise exc
django.db.utils.OperationalError: (2003, "Can't connect to MySQL server on '127.0.0.1' ([Errno 111] Connection refused)")

I tried changing the MYSQL_HOST to localhost or 127.0.0.1 (by default) or the WAN ip address assigned to the virtual machine, but none of it works.

Answer 1

set MYSQL_HOST environment variable to mysql when run myblog container

eg: docker run -d -e MYSQL_HOST=mysql --name myblog myblog

if you are using default network you've to use --link option or create another network for it:

eg:

1. docker network create mynetwork
2. docker connect mynetwork myblog
3. docker connect mynetwork mysql