How to use nginx as a proxy with Express and docker-compose?

Hi guys, I experience a strange behavior with my Express Server (Node.js) configuration. I have a docker-compose setup with a couple of apps (Rails, Postrges, Express and Express): version: ‘2’

services:
  db:
    image: postgres
    env_file: .env
    volumes:
      - ./postgres-data:/var/lib/postgresql/data
  app:
    image: app-image
    volumes:
      - ./public:/usr/src/app/public
    env_file: .env
    environment:
      RAILS_ENV: production
    depends_on:
      - db
    links:
      - db
    expose:
      - "3000"
  ui:
    image: ui-image
    ports:
      - "4000:4000"
  proxy:
    build:
      context:  ./nginx
      dockerfile: Dockerfile
    ports:
      - "3000:3000"
      - "80:80"
    links:
      - app
      - ui

nginx.conf:

worker_processes 4;
 
events { worker_connections 1024; }
 
http {
	sendfile on;
    
	upstream ui {
		server app:3000;
	}

	upstream ui {
		server ui:4000;
        }


	server {
		listen 3000;

		location / {
			proxy_set_header  X-Real-IP  $remote_addr;
    			proxy_set_header  X-Forwarded-For $proxy_add_x_forwarded_for;
    			proxy_set_header Host $http_host;
    			proxy_pass http://app;
		}
	}
 
	server {
	listen 80;
         
		location / {
			proxy_pass http://node-app;
		}

	}
}

server.ts:

// Express server
const app = express();
[...]
app.listen(4000, () => {
  console.log('listening at 4000');
});

Let’s say that my public IP is 188.222.22.22 I can reach my Rails app at 188.222.22.22:3000 (using nginx as a proxy), I can reach my ui app at 188.222.22.22:4000 (without nginx) but I can not get UI at 188.222.22.22. I was trying with several configs and nothing works.

188.222.22.22 gives me 502 Bad Gateway, this is what I found in logs: 1 connect() failed (111: Connection refused) while connecting to upstream

Thanks!