Ubuntu – Connecting a Docker-ized Django app to local Postgresql database

For deployment purposes, I have set up my Django app in a Docker container. The setup works, and I am able to serve it using Gunicorn and Apache. However, I can’t seem to access my Postgresql database anymore. This database is running locally, and I have no problem accessing it when launching my Django app from outside the container.

But when I launch my app from inside the Docker container, all I get is this error:

django.db.utils.OperationalError: connection to server at "127.0.0.1", port 5433 failed: Connection refused
Is the server running on that host and accepting TCP/IP connections?

Clearly I am not the first one having trouble with this.

I have made sure that Postgresql is listening to external adresses, as stated here, so this shouldn’t be a problem.

I have also tried playing around with my Docker compose configuration file. Using network_mode=host is not compatible with port bindings. Back in network_mode=bridge, I have also tried as upvoted here :

extra_hosts:
    - "host.docker.internal:host-gateway"

But it does not change anything, nor does replacing 127.0.0.1 with 172.17.0.0 in my Django .env file.
I am a bit at a loss here, so any insight would be appreciated. I have to say that I am new to Docker, so maybe I’m missing something obvious.

I’m working with Ubuntu 22.04, Docker 24.0, Django 4.2, Postgresql 14. Here is my really simple docker-compose.yml :

services:
  web:
    build: ./
    command: gunicorn main.wsgi:application --bind 0.0.0.0:8000
    ports:
      - 8000:8000
    env_file:
      - ./main/.env

And a sample .env file :

DATABASE_NAME=db_name
DATABASE_USER=db_user
DATABASE_PASSWORD=password
DATABASE_HOST=127.0.0.1
DATABASE_PORT=port

Thanks by advance !