2002, "Can't connect to local MySQL server through socket '/run/mysqld/mysqld.sock' (2)" in docker-compose up

Question

I'm trying to start the server through docker-compose up

I'm get an error:

2002, "Can't connect to local MySQL server through socket '/run/mysqld/mysqld.sock' (2)"

docker-compose.yml

version: '3'

services:
  db:
    image: mysql:5.7
    environment:
       MYSQL_DATABASE: 'slack_bot1'
       MYSQL_USER: 'root'
       MYSQL_PASSWORD: ''
       MYSQL_ROOT_PASSWORD: '****'
    volumes:
      - /opt/slack_bot/mysql_data:/var/lib/mysql
  redis:
    image: "redis:alpine"
    volumes:
      - /opt/slack_bot/redis_data:/var/lib/redis
  web:
    build: .
    command: python manage.py runserver 0.0.0.0:8001
    ports:
      - "8001:8001"
    depends_on:
      - db

Dockerfile

FROM python:3.7-alpine
ENV PYTHONUNBUFFERED 1
WORKDIR /home/slack_bot
ADD requirements.txt /home/slack_bot/
RUN set -e; \
        apk add --no-cache --virtual .build-deps \
                gcc \
                libc-dev \
                linux-headers \
                mariadb-dev \
                python3-dev \
        ;
RUN pip install -r requirements.txt
ADD . /home/slack_bot/
EXPOSE 8001
CMD ["python", "manage.py",  "runserver", "0.0.0.0:8001"]

docker ps log

CONTAINER ID        IMAGE                                  COMMAND                  CREATED             STATUS                          PORTS                                                                                                                                         NAMES
68b61ca0ce74        slack_bot_web                          "python manage.py ru…"   8 minutes ago       Up 32 seconds                   0.0.0.0:8001->8001/tcp                                                                                                                        slack_bot_web_1
c5f254a527b0        mysql:5.7                              "docker-entrypoint.s…"   8 minutes ago       Up 34 seconds                   3306/tcp, 33060/tcp                                                                                                                           slack_bot_db_1
4cbc1fa3765e        redis:alpine                           "docker-entrypoint.s…"   15 minutes ago      Up 33 seconds                   6379/tcp                                                                                                                                      slack_bot_redis_1

Django settings of database

        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'slack_bot1',
        'USER': 'root',
        'PASSWORD': '',
        'HOST': '',
        'PORT': '',

Answer 1

I was able to connect django and db docker containers which are in the same machine but aren't in the same docker-compose file by the following steps:

• Use host.docker.internal as host in settings.py instead of localhost as following:

    DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'dbName',
        'USER': 'dbUser',
        'PASSWORD': 'dbUserPassword',
        'HOST': 'host.docker.internal',
        'PORT': '3306'
    }
  

  }

• Expose the port in db compose-file

    ports:
      - 3306:3306
  

Answer 2

In your django settings, you leave database host as EMPTY, then the default value would be localhost. When use localhost, mysql client driver will connect mysql server with unix socket not tcp.

So, for your case you need to export unix socket in your mysql container to volume, then your django app container utilize this volume to share the unix socket.

Next is what you needed to do:

1. Manual new a folder which later as volume to share your unix socket file

   (IMPORTANT: you could not rely on docker-compose to new this folder, you will encountered permission error)

   mkdir -p /tmp/slack_bot/mysqld && chmod -R 777 /tmp/slack_bot/mysqld
   

2. In your docker-compose.yaml, add one more volume to mysql service:

   db:
       image: mysql:5.7
       environment:
          MYSQL_DATABASE: 'slack_bot1'
          MYSQL_USER: 'root'
          MYSQL_PASSWORD: ''
          MYSQL_ROOT_PASSWORD: '****'
       volumes:
         - /opt/slack_bot/mysql_data:/var/lib/mysql
         - /tmp/slack_bot/mysqld:/var/run/mysqld
   

3. In your docker-compose.yaml, add one more volume to web service:

   web:
       build: .
       command: python manage.py runserver 0.0.0.0:8001
       ports:
         - "8001:8001"
       depends_on:
         - db
       volumes:
         - /tmp/slack_bot/mysqld:/run/mysqld
   

   NOTE: here you say you get the error /run/mysqld/mysqld.sock as next, I'm not sure if you paste the all log as most offen it could be /var/run/mysqld/mysqld.sock, nertheless, if the error is /var/run/mysqld/mysqld.sock then you should modify above example volume to - /tmp/slack_bot/mysqld:/var/run/mysqld

   2002, "Can't connect to local MySQL server through socket '/run/mysqld/mysqld.sock' (2)"

With above, now your web service could share the unix socket in mysql container.

Additional, configure HOST as db I think also could be another solution, just unix socket is much faster compared to use tcp.