Solving the Infamous “Can’t Connect Local Django to Postgresql Container Due to Credentials” Issue

This mismatch is the root cause of the “can’t connect” issue. But fear not, dear developer, for we have a solution!

Step 1: Set Up Your PostgreSQL Container

Let’s start by creating a PostgreSQL container using Docker. You can use the following command:

docker run -d --name my-postgres -e POSTGRES_USER=myuser -e POSTGRES_PASSWORD=mypassword -e POSTGRES_DB=mydb -p 5432:5432 postgres

This command creates a new PostgreSQL container named `my-postgres`, with the specified environment variables:

• `POSTGRES_USER`: The username for the PostgreSQL database.
• `POSTGRES_PASSWORD`: The password for the PostgreSQL database.
• `POSTGRES_DB`: The name of the PostgreSQL database.

Make a note of these credentials, as we’ll need them later.

Step 2: Configure Your Django Project

Now, let’s move on to our Django project. We need to update the `settings.py` file to use the PostgreSQL container’s credentials.

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'mydb',
        'USER': 'myuser',
        'PASSWORD': 'mypassword',
        'HOST': 'my-postgres',  # Use the container name as the hostname
        'PORT': '5432',
    }
}

Notice the `HOST` parameter, where we’re using the container name `my-postgres` as the hostname. This tells Django to connect to the container instead of `localhost`.

Step 3: Handle the Credential Mismatch

Even with the updated `settings.py`, we still need to handle the credential mismatch. We can do this by creating a `docker-compose.yml` file that bridges the gap between our local machine and the PostgreSQL container.

version: '3'

services:
  my-postgres:
    image: postgres
    environment:
      - POSTGRES_USER=myuser
      - POSTGRES_PASSWORD=mypassword
      - POSTGRES_DB=mydb
    ports:
      - "5432:5432"
    volumes:
      - ./pgdata:/var/lib/postgresql/data

  django:
    build: .
    command: python manage.py runserver 0.0.0.0:8000
    volumes:
      - .:/code
    ports:
      - "8000:8000"
    depends_on:
      - my-postgres
    environment:
      - DATABASE_URL=postgres://myuser:mypassword@my-postgres:5432/mydb

This `docker-compose.yml` file defines two services: `my-postgres` and `django`. The `my-postgres` service uses the same environment variables as before, and the `django` service builds our Django project and maps the `DATABASE_URL` environment variable to the PostgreSQL container’s credentials.

Step 4: Run Your Application

Finally, let’s run our application using Docker Compose:

docker-compose up -d

This command starts both services in detached mode. You can now access your Django project at `http://localhost:8000`.

Troubleshooting Tips

If you’re still encountering issues, here are some troubleshooting tips:

• Check your container logs**: Use `docker-compose logs -f my-postgres` to check the PostgreSQL container logs for any errors.
• Verify your credentials**: Double-check that your `DATABASE_URL` environment variable is correct and matches the credentials in your `docker-compose.yml` file.
• Update your `settings.py`**: Make sure your `settings.py` file is updated with the correct credentials and hostname.