Failing to connect to mysql server when I change port number - mysql

Question

I attempted to change MYSQL container to run on a different port number ie 3307 in my docker-compose file but I get a database connection error as shown below after launching services with docker-compose up what could be the issue?
web_1 | Traceback (most recent call last):
web_1 | File "/usr/local/lib/python3.7/site-packages/django/db/backends/base/base.py", line 216, in ensure_connection
web_1 | self.connect()
web_1 | File "/usr/local/lib/python3.7/site-packages/django/db/backends/base/base.py", line 194, in connect
web_1 | self.connection = self.get_new_connection(conn_params)
web_1 | File "/usr/local/lib/python3.7/site-packages/django/db/backends/mysql/base.py", line 227, in get_new_connection
web_1 | return Database.connect(**conn_params)
web_1 | File "/usr/local/lib/python3.7/site-packages/MySQLdb/__init__.py", line 130, in Connect
web_1 | return Connection(*args, **kwargs)
web_1 | File "/usr/local/lib/python3.7/site-packages/MySQLdb/connections.py", line 185, in __init__
web_1 | super().__init__(*args, **kwargs2)
web_1 | MySQLdb._exceptions.OperationalError: (2002, "Can't connect to MySQL server on 'db' (115)")
web_1 |
web_1 | The above exception was the direct cause of the following exception:
web_1 |
web_1 | Traceback (most recent call last):
web_1 | File "/usr/local/lib/python3.7/site-packages/gunicorn/arbiter.py", line 583, in spawn_worker
web_1 | worker.init_process()
web_1 | File "/usr/local/lib/python3.7/site-packages/gunicorn/workers/base.py", line 129, in init_process
web_1 | self.load_wsgi()
web_1 | File "/usr/local/lib/python3.7/site-packages/gunicorn/workers/base.py", line 138, in load_wsgi
web_1 | self.wsgi = self.app.wsgi()
web_1 | File "/usr/local/lib/python3.7/site-packages/gunicorn/app/base.py", line 67, in wsgi
web_1 | self.callable = self.load()
web_1 | File "/usr/local/lib/python3.7/site-packages/gunicorn/app/wsgiapp.py", line 52, in load
web_1 | return self.load_wsgiapp()
web_1 | File "/usr/local/lib/python3.7/site-packages/gunicorn/app/wsgiapp.py", line 41, in load_wsgiapp
web_1 | return util.import_app(self.app_uri)
web_1 | File "/usr/local/lib/python3.7/site-packages/gunicorn/util.py", line 350, in import_app
web_1 | __import__(module)
web_1 | File "/src/core/wsgi.py", line 16, in <module>
web_1 | application = get_wsgi_application()
web_1 | File "/usr/local/lib/python3.7/site-packages/django/core/wsgi.py", line 12, in get_wsgi_application
web_1 | django.setup(set_prefix=False)
web_1 | File "/usr/local/lib/python3.7/site-packages/django/__init__.py", line 24, in setup
web_1 | apps.populate(settings.INSTALLED_APPS)
web_1 | File "/usr/local/lib/python3.7/site-packages/django/apps/registry.py", line 120, in populate
web_1 | app_config.ready()
web_1 | File "/usr/local/lib/python3.7/site-packages/django_prometheus/apps.py", line 23, in ready
web_1 | ExportMigrations()
web_1 | File "/usr/local/lib/python3.7/site-packages/django_prometheus/migrations.py", line 49, in ExportMigrations
web_1 | executor = MigrationExecutor(connections[alias])
web_1 | File "/usr/local/lib/python3.7/site-packages/django/db/migrations/executor.py", line 18, in __init__
web_1 | self.loader = MigrationLoader(self.connection)
web_1 | File "/usr/local/lib/python3.7/site-packages/django/db/migrations/loader.py", line 49, in __init__
web_1 | self.build_graph()
web_1 | File "/usr/local/lib/python3.7/site-packages/django/db/migrations/loader.py", line 212, in build_graph
web_1 | self.applied_migrations = recorder.applied_migrations()
web_1 | File "/usr/local/lib/python3.7/site-packages/django/db/migrations/recorder.py", line 61, in applied_migrations
web_1 | if self.has_table():
web_1 | File "/usr/local/lib/python3.7/site-packages/django/db/migrations/recorder.py", line 44, in has_table
web_1 | return self.Migration._meta.db_table in self.connection.introspection.table_names(self.connection.cursor())
web_1 | File "/usr/local/lib/python3.7/site-packages/django/db/backends/base/base.py", line 255, in cursor
web_1 | return self._cursor()
web_1 | File "/usr/local/lib/python3.7/site-packages/django/db/backends/base/base.py", line 232, in _cursor
web_1 | self.ensure_connection()
web_1 | File "/usr/local/lib/python3.7/site-packages/django/db/backends/base/base.py", line 216, in ensure_connection
web_1 | self.connect()
web_1 | File "/usr/local/lib/python3.7/site-packages/django/db/utils.py", line 89, in __exit__
web_1 | raise dj_exc_value.with_traceback(traceback) from exc_value
web_1 | File "/usr/local/lib/python3.7/site-packages/django/db/backends/base/base.py", line 216, in ensure_connection
web_1 | self.connect()
web_1 | File "/usr/local/lib/python3.7/site-packages/django/db/backends/base/base.py", line 194, in connect
web_1 | self.connection = self.get_new_connection(conn_params)
web_1 | File "/usr/local/lib/python3.7/site-packages/django/db/backends/mysql/base.py", line 227, in get_new_connection
web_1 | return Database.connect(**conn_params)
web_1 | File "/usr/local/lib/python3.7/site-packages/MySQLdb/__init__.py", line 130, in Connect
web_1 | return Connection(*args, **kwargs)
web_1 | File "/usr/local/lib/python3.7/site-packages/MySQLdb/connections.py", line 185, in __init__
web_1 | super().__init__(*args, **kwargs2)
web_1 | django.db.utils.OperationalError: (2002, "Can't connect to MySQL server on 'db' (115)")
Docker Compose File
db:
restart: always
image: mysql:5.7
command: --default-authentication-plugin=mysql_native_password
environment:
MYSQL_ROOT_PASSWORD: test
MYSQL_DATABASE: default_schema
MYSQL_USER: test
MYSQL_PASSWORD: test
expose:
- "3307"
ports:
- "3307:3307"
volumes:
- ../mysql-data:/var/lib/mysql
phpmyadmin:
image: phpmyadmin/phpmyadmin
container_name: pma
links:
- db
environment:
PMA_HOST: db
PMA_PORT: 3307
PMA_ARBITRARY: 1
restart: always
ports:
- 8183:80
Application DB Settings
DATABASES = {
'default': {
'ENGINE': 'django.db.backends.mysql',
'NAME': 'default_schema',
'USER': 'root',
'PASSWORD': 'test',
'HOST': 'db',
'PORT': '3307',
}
}
After running docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
2d60c0265ed9 nllb_frontend "/docker-entrypoint.…" 7 seconds ago Up 6 seconds 0.0.0.0:80->80/tcp frontend
323a7dd77121 nllb_web "gunicorn --bind 0.0…" 7 seconds ago Up 2 seconds 7000/tcp nllb_web_1
89ad90d1fb10 phpmyadmin/phpmyadmin "/docker-entrypoint.…" 7 seconds ago Up 6 seconds 0.0.0.0:8183->80/tcp pma
e5c5e2bda22c mysql:5.7 "docker-entrypoint.s…" 8 seconds ago Up 7 seconds 3306/tcp, 33060/tcp, 0.0.0.0:3307->3307/tcp nllb_db_1
1332ad2e136b redis:latest "docker-entrypoint.s…" 9 seconds ago Up 8 seconds 6379/tcp nllb_redis_1

Answer 1

You need to also tell MySQL about the change of plans:
environment:
MYSQL_TCP_PORT: 3307
(fixed, thanks to #derpirscher, see below)
(I previously guessed it would be PORT, DB_PORT, MYSQL_PORT, MYSQLD_PORT, or, as a testament to my willingness to believe any absurdity I find on Github, MYSQL_HOST=db:3307)

Answer 2

Connections between containers always use the "normal" port number for the service; these connections ignore any remapping that ports: might do. If you are only connecting to the database from another container, in fact, ports: isn't required at all; if it is present, the second port number again needs to be the "normal" port number for the service.
It should work to change the docker-compose.yml file:
version: '3.8'
services:
db:
# do not need `expose:`
ports: # optional, if you're not going to connect from outside Docker
- '3307:3306' # second port _must_ be "normal" port 3306
phpmyadmin:
# do not need `container_name:` or `links:`
environment:
PMA_HOST: db # Compose service name
PMA_PORT: 3306 # always the "normal" port, ignores `ports:`
And similarly in your configuration:
'HOST': 'db',
'PORT': '3306', # the "normal" port, ignores `ports:`
As I noted in comments, expose: and links: are only relevant for an outdated mode of Docker networking, and can be safely removed from the docker-compose.yml file. There's also usually no harm in letting Compose pick its own container_name:.