Deploying a MERN (MongoDB, Express.js, React.js, Node.js) application on a DigitalOcean Droplet and setting up multiple domain names can be a smooth process with the right configuration. In this guide, we’ll walk through deploying a MERN app and configuring Nginx as a reverse proxy to serve multiple domains.

Step 1: Setting Up a DigitalOcean Droplet

1. Create a Droplet on DigitalOcean with Ubuntu 20.04 or later.
2. Connect via SSH: ssh root@your_server_ip
3. Update and Upgrade Packages: sudo apt update && sudo apt upgrade -y

Step 2: Install Node.js and MongoDB

1. Install Node.js: curl -fsSL https://deb.nodesource.com/setup_18.x | sudo -E bash - sudo apt install -y nodejs
2. Install MongoDB: sudo apt install -y mongodb sudo systemctl start mongodb sudo systemctl enable mongodb
3. Verify Installations: node -v mongo --version

Step 3: Deploy Your MERN Application

1. Clone Your MERN App from GitHub

Public Git Repository

cd /var/www
sudo git clone git@github.com:yourusername/your-mern-app.git
cd your-mern-app

Private Git Repository

sudo ssh-keygen

Select path (/root/.ssh/[id_name])

sudo cat /root/.ssh/[id_name].pub

Config

sudo nano /root/.ssh/config

#example
Host repo-name
Hostname github.com
User git
IdentityFile /root/.ssh/[id_name]

#Note - you have to duplicate the above for multiple repositories

Paste the key in your github repo > settings > deploy keys

Now lets clone the git repo using ssh key

git clone git@github.com:github_username/repo-name.git

If you have multiple github repositories then do like this

GIT_SSH_COMMAND="ssh -i /root/.ssh/[id_name]" git clone git@github.com:your-github-username/repo-name.git

2. Install Dependencies

cd backend
npm install

cd ../frontend
npm install

3. Start Frontend & Backend Server

Installing pm2

sudo npm install -g pm2

cd backend

sudo pm2 start npm --name "backend" -- start

4. Start Frontend

cd frontend

sudo pm2 start npm --name "frontend" -- start

Step 4: Install and Configure Nginx

Install Nginx:

sudo apt install nginx -y

Create a New Nginx Configuration File:

sudo nano /etc/nginx/sites-available/mern-app

Add the following:

server {
    listen 80;
    server_name admin.yourdomain.com;
    location / {
        proxy_pass http://localhost:3000;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;
    }
}

server {
    listen 80;
    server_name client.yourdomain.com;
    location / {
        proxy_pass http://localhost:4000;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;
    }
}

Enable the Config and Restart Nginx:

sudo ln -s /etc/nginx/sites-available/mern-app /etc/nginx/sites-enabled/

sudo nginx -t  # Check for syntax errors

sudo systemctl restart nginx

Step 5: Configure DNS for Multiple Domains

1. Go to your DNS provider (GoDaddy, Cloudflare, Namecheap, etc.).
2. Create A records:
   • admin.yourdomain.com → your_droplet_IP
   • client.yourdomain.com → your_droplet_IP
3. Save changes and wait for propagation (can take a few minutes).

Step 6: Secure with SSL (Optional but Recommended)

Install Certbot for free Let’s Encrypt SSL:

sudo apt install certbot python3-certbot-nginx -y

Run the SSL command:

sudo certbot --nginx -d admin.yourdomain.com -d client.yourdomain.com

Certbot will automatically configure Nginx for SSL.

Auto-Renew SSL:

sudo certbot renew --dry-run

Step 7: Verify Deployment

• Open a browser and go to:
  • https://admin.yourdomain.com → Should serve backend/admin panel.
  • https://client.yourdomain.com → Should serve frontend/client.
• If everything works fine, your deployment is successful! 🚀

Conclusion

In this guide, we deployed a MERN application on DigitalOcean with multiple domain names using Nginx as a reverse proxy. We also set up SSL for security and DNS for domain routing.

Now your app is production-ready! Let me know if you need any modifications. 🚀