🌐 Mastering Subdomains on DigitalOcean: A Step-by-Step Guide with Nginx & SSL

If you have a primary domain (e.g., azan.lk) hosted on DigitalOcean, adding subdomains like dev.azan.lk is a simple process. In this guide, we’ll show you how to create subdomains, configure Nginx, and secure them with Let’s Encrypt SSL.

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Prerequisites

1. A DigitalOcean droplet running Ubuntu 24.04.

2. Your primary domain (azan.lk) already pointing to DigitalOcean nameservers.

3. SSH access to your droplet.
   Check this guide for secure SSH setup: Fortify Your DigitalOcean Droplet.

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Step 1 — SSH Into Your Server

ssh deploy_user

Navigate to the web root directory:

cd /var/www/html

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Step 2 — Create Subdomain Directory

Create a folder for your subdomain:

sudo mkdir dev.azan.lk
sudo chown -R $USER:$USER /var/www/html/dev.azan.lk

cd /var/www/html/dev.azan.lk

Add a test PHP file to verify everything works:

nano index.php

<?php phpinfo();?>

Adjust permissions:

sudo chown -R $USER:www-data .
sudo find . -type f -exec chmod 664 {} \;

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Step 3 — Configure Nginx for the Subdomain

Create a new server block:

cd /etc/nginx/sites-available
sudo vim dev.azan.lk

Paste the following configuration:

server {
    listen 80;
    listen [::]:80;

    server_name dev.azan.lk;
    root /var/www/html/dev.azan.lk;

    index index.php;
    charset utf-8;

    add_header X-Frame-Options "SAMEORIGIN";
    add_header X-Content-Type-Options "nosniff";

    location / {
        try_files $uri $uri/ /index.php?$query_string;
    }

    location = /favicon.ico { access_log off; log_not_found off; }
    location = /robots.txt  { access_log off; log_not_found off; }

    error_page 404 /index.php;

    location ~ ^/index\.php(/|$) {
        fastcgi_pass unix:/var/run/php/php8.4-fpm.sock;
        fastcgi_param SCRIPT_FILENAME $realpath_root$fastcgi_script_name;
        include fastcgi_params;
        fastcgi_hide_header X-Powered-By;
    }

    location ~ /\.(?!well-known).* {
        deny all;
    }
}

Enable the site and test Nginx:

sudo ln -s /etc/nginx/sites-available/dev.azan.lk /etc/nginx/sites-enabled
sudo nginx -t
sudo systemctl restart nginx

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Step 4 — Configure DNS in DigitalOcean

You have two options:

Option 1 — CNAME (points to main domain)

Option 2 — A Record (points directly to server IP)

Replace 123.45.67.89 with your droplet’s public IP.
A direct A record is slightly faster and simpler.

After updating the DNS Records

1. Wait a few minutes for DNS to propagate (TTL matters).

2. Test from your machine:

nslookup dev.azan.lk
ping dev.azan.lk

If it resolves to your server IP → browser will reach Nginx.

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Step 5 — Enable SSL with Let’s Encrypt

If you see this warning when accessing your subdomain:

Your connection is not private
net::ERR_CERT_COMMON_NAME_INVALID

Install Certbot and enable HTTPS:

sudo apt install certbot python3-certbot-nginx -y
sudo certbot --nginx -d dev.azan.lk

sudo certbot renew --dry-run

Follow the prompts:

• Enter your email for renewal notifications.

• Agree to Let’s Encrypt terms.

• Choose to redirect HTTP to HTTPS.

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Step 6 — Test Your Subdomain

Visit https://dev.azan.lk. You should see the PHP info page, confirming your subdomain is live and secured.

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✅ Summary

• Subdomains are just directories with their own Nginx configuration.

• DigitalOcean lets you manage DNS and subdomains easily.

• Let’s Encrypt SSL keeps your subdomains secure and trusted.