无法将主机名转换为“db”到地址：未知主机

Question

I'm attempting to follow the guide provided by: https://docs.docker.com/compose/django/ Whenever I attempt to makemigrations, it gives me the Unknown host error given in the title. I'm trying to use PostgreSQL with Django and Wagtail as its CMS

My docker-compose.yml looks like:

version: "3.9"
   
services:
  db:
    image: postgres
    environment:
      - POSTGRES_DB=postgres
      - POSTGRES_USER=postgres
      - POSTGRES_PASSWORD=postgres
  web:
    build: .
    command: python manage.py runserver 0.0.0.0:8000
    volumes:
      - .:/code
    ports:
      - "8000:8000"
    depends_on:
      - db

and my settings in the settings.py file look like:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'postgres',
        'USER': 'postgres',
        'PASSWORD': 'postgres',
        'HOST': 'db',
        'PORT': 5432,
    }
}

Am I missing anything?

Answer 1

Your code can run in two different environments, and hard-coding the connection information might not be correct.

You mention in a comment that you're running something like:

docker-compose up -d db
python manage.py makemigrations

In this environment python is running outside of Docker. If you add ports: [5432:5432] to the database configuration in the docker-compose.yml file, the database will be accessible via (probably) localhost . On the other hand, when you run docker-compose up , the application runs inside Docker and the database will be reachable at db .

You can use an environment variable to configure this. I find it useful to give these variables default values that would be useful for a developer, and set them to different values in my deployment setup (the docker-compose.yml ).

DATABASES = {
    'default': {
        ...
        'HOST': os.getenv('DB_HOST', 'localhost'),
        ...
    }
}

version: "3.9"
services:
  db:
    ports:
      - '5432:5432' # makes this accessible from your development environment
    ...
  web:
    environment:
      - DB_HOST=db
    ...