could not translate host name to "db" to address: Unknown host

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?

You should run the management commands from the web container. Try `docker-compose run --rm web python manage.py makemigrations` — Iain Shelvington, Jan 09 '21 at 02:27
Thank you! That didn't give me an error. However, now I have wagtailcore.site does not exist? Should I make a new question regarding this? — vice, Jan 09 '21 at 02:30
Happy to help. Sounds like a separate issue, a new question is probably appropriate — Iain Shelvington, Jan 09 '21 at 02:32
I was just blanking out, I quickly realized I didn't migrate, thank you again! — vice, Jan 09 '21 at 02:33

score 2 · Accepted Answer · answered Jan 09 '21 at 12:27

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
    ...

score 0 · Answer 2 · answered May 26 '23 at 10:53

In my situation both db and localhost did not work. So I set settings.py to:

DATABASES = { 
        "default": {
         ...
        'HOST': 'host.docker.internal',
        ...

    }
}

Which allows one docker container to access all other containers similar to localhost. Source of idea: https://stackoverflow.com/a/62147846/7924573

could not translate host name to "db" to address: Unknown host

2 Answers2

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