Run Multiple Services on the Same Port Using a Reverse Proxy

A reverse proxy allows multiple services to share the same port by routing incoming requests based on domain or path. This is commonly used with web apps, APIs, and Docker containers on a VPS.

Step 1: Understand How a Reverse Proxy Works

The reverse proxy listens on a public port (usually 80 or 443) and forwards requests internally to different services running on separate ports.

Step 2: Install Nginx

Nginx is a lightweight and reliable reverse proxy.

sudo apt update
sudo apt install nginx -y

Start and enable Nginx:

sudo systemctl enable nginx
sudo systemctl start nginx

Step 3: Run Services on Different Internal Ports

Ensure each service runs on a unique local port.

# Example
App 1 → localhost:3000
App 2 → localhost:4000

Step 4: Configure Nginx for Domain-Based Routing

Create a new server block configuration.

sudo nano /etc/nginx/sites-available/app1.conf

server {
    listen 80;
    server_name app1.example.com;

    location / {
        proxy_pass http://localhost:3000;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
    }
}

Enable the configuration:

sudo ln -s /etc/nginx/sites-available/app1.conf /etc/nginx/sites-enabled/
sudo nginx -t
sudo systemctl reload nginx

Step 5: Add a Second Service on the Same Port

Repeat the process for another domain.

sudo nano /etc/nginx/sites-available/app2.conf

server {
    listen 80;
    server_name app2.example.com;

    location / {
        proxy_pass http://localhost:4000;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
    }
}

Enable and reload Nginx:

sudo ln -s /etc/nginx/sites-available/app2.conf /etc/nginx/sites-enabled/
sudo nginx -t
sudo systemctl reload nginx

Step 6: Verify Reverse Proxy Setup

Test each domain in the browser or via curl.

curl http://app1.example.com
curl http://app2.example.com

Both services should be accessible through port 80.

Step 7: Secure Services with HTTPS

For production environments, secure services with SSL.

You may also want to review this related article: Fix Port Already in Use Error on Linux

Optional Step: Path-Based Routing

Route services using URL paths instead of domains.

location /api/ {
    proxy_pass http://localhost:3000;
}