Nginx reverse proxy

Rather than exposing port 3000 or 8080 on the Internet, have Nginx listen on 80/443 and forward traffic to your local application. Standard pattern on a HolyCloud Linux VPS hosting APIs, panels, or Docker containers.

Prerequisites

• Nginx installed (apt install nginx)
• Application listening locally (e.g. 127.0.0.1:3000)
• Domain name and TLS certificate (see « Nginx and Certbot ») recommended
• UFW: only 80/443 public

Step 1: example backend application

# Exemple : conteneur sur le port 3000
docker run -d --name app -p 127.0.0.1:3000:3000 votre-image:tag
curl -sI http://127.0.0.1:3000

The application should be reachable on localhost only when possible.

Step 2: reverse proxy configuration

sudo nano /etc/nginx/sites-available/app.example.com

upstream app_backend {
    server 127.0.0.1:3000;
    keepalive 32;
}

server {
    listen 80;
    listen [::]:80;
    server_name app.example.com;

    location / {
        return 301 https://$host$request_uri;
    }
}

server {
    listen 443 ssl http2;
    listen [::]:443 ssl http2;
    server_name app.example.com;

    # Chemins Certbot — adaptez si nécessaire
    ssl_certificate     /etc/letsencrypt/live/app.example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/app.example.com/privkey.pem;

    location / {
        proxy_pass http://app_backend;
        proxy_http_version 1.1;
        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-Proto $scheme;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_read_timeout 90s;
    }
}

Enable the site:

sudo ln -sf /etc/nginx/sites-available/app.example.com /etc/nginx/sites-enabled/
sudo nginx -t && sudo systemctl reload nginx

Step 3: multiple services (paths)

location /api/ {
    proxy_pass http://127.0.0.1:4000/;
}

location / {
    proxy_pass http://127.0.0.1:3000/;
}

Watch the trailing slash on proxy_pass to keep or strip the /api prefix.

Step 4: limits and logs

sudo nano /etc/nginx/nginx.conf

In the http block, adjust if needed:

client_max_body_size 50M;

Per-site logs: access_log /var/log/nginx/app.example.com.access.log;

Verification

curl -sI https://app.example.com
curl -s https://app.example.com/health
sudo tail -f /var/log/nginx/error.log

From outside, port 3000 must not be reachable:

sudo ufw status | grep 3000

Need help?

• 502 Bad Gateway: backend stopped or wrong port — curl http://127.0.0.1:3000, docker ps
• WebSocket drops: check Upgrade / Connection headers
• Support: nginx -t, vhost excerpt (no private key), container/service status