Nginx proxy pass to dockerized gunicorn server

I try to deploy an app with the following architecture:

• the backend is based on a dockerized Django Rest Framework with gunicorn listening on 127.0.0.1:8000
• the frontend is based on VueJS (not dockerized) and make calls to my backend API routes
• NginX is used to serve frontend pages and to proxy API requests to gunicorn

Here is an excerpt of my backend docker-compose file:

  server:
    build:
      context: .
      dockerfile: ./docker/server/Dockerfile
    image: myserverimage
    command: 'gunicorn --bind=127.0.0.1:8000 --workers=3 my_backend.wsgi:application'
    ports:
      - 8000:8000

docker-compose up tells me everything looks fine for this part (server started and gunicorn is listening on 127.0.0.1:8000)

And here is the server block from nginx config:

upstream backend {
                server 127.0.0.1:8000;
        }

server {
                listen 443 default_server ssl;
                server_name  mydomain.com;
                ssl_certificate /etc/nginx/ssl/nginx.crt;
                ssl_certificate_key /etc/nginx/ssl/nginx.key;

                access_log /var/log/nginx/mydomain.access.log;

                location / {
                        root   /path/to/vue/project/dist;
                        index  index.html;
                        try_files $uri $uri/ /index.html;
                }

                location /backend/ {
                        proxy_pass http://backend/;
                        proxy_http_version 1.1;
                        proxy_set_header Upgrade $http_upgrade;
                        proxy_set_header Connection "upgrade";

                        proxy_set_header Host $host;
                        proxy_set_header X-Real-IP $remote_addr;
                        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
                        proxy_set_header X-Forwarded-Host $server_name;
                }

  }

I can access to my frontend pages at mydomain.com but requests to mydomain.com/backend return 502 bad gateway error.

If I change 127.0.0.1:8000 to backend-container-ip:8000 in both nginx upstream declaration and gunicorn command, it works.

So my question is: is there a way to configure such architecture whitout having to know the container ip (I don’t want to hardcode it, especially in the docker-compose declaration) ?
Should I create an additional container with nginx, even if my frontend is not based on the docker-compose definition ?