When you need to expose a service running on a non-standard port (e.g., 10000) through a clean hostname like mywebapp.mydomain on port 80/443, DNS alone can't solve the port-mapping problem. Here's why:

• DNS resolves names to IPs only
• Port specifications require application-layer solutions

Option 1: Reverse Proxy (Recommended)

Using Nginx as reverse proxy:

server {
    listen 80;
    server_name mywebapp.mydomain;

    location / {
        proxy_pass http://localhost:10000;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
    }
}

Option 2: Port Forwarding with Rinetd

/etc/rinetd.conf configuration:

0.0.0.0 80 myserver.mydomain 10000

Note: This will forward all port 80 traffic, so use judiciously.

Option 3: SRV Records (Advanced DNS)

While not HTTP-compatible, some protocols support SRV records:

_service._proto.mywebapp.mydomain. IN SRV 10 5 10000 myserver.mydomain.

Complete workflow for Nginx solution:

1. Create DNS record: mywebapp IN CNAME myserver
2. Install Nginx: sudo apt install nginx
3. Create config at /etc/nginx/sites-available/mywebapp
4. Enable site: ln -s /etc/nginx/sites-available/mywebapp /etc/nginx/sites-enabled/
5. Test config: nginx -t
6. Reload: systemctl reload nginx

• Always use HTTPS for production (certbot + Let's Encrypt)
• Restrict source IPs when possible
• Monitor proxy connection counts

Standard DNS resolution only handles hostname-to-IP mapping without port specification. When you create a CNAME like mywebapp.mydomain → myserver.mydomain, it doesn't solve the port requirement (10000 in your case). Here are three practical approaches:

# Nginx configuration example
server {
    listen 80;
    server_name mywebapp.mydomain;

    location / {
        proxy_pass http://myserver.mydomain:10000;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
    }
}

For web applications, implement HTTP 301/302 redirect:

# Python Flask example
from flask import Flask, redirect

app = Flask(__name__)

@app.route('/')
def redirect_to_port():
    return redirect("http://myserver.mydomain:10000", code=302)

Using iptables for Linux systems:

sudo iptables -t nat -A PREROUTING -p tcp --dport 80 -j DNAT \
--to-destination myserver.mydomain:10000
sudo iptables -t nat -A POSTROUTING -j MASQUERADE

While mostly used for non-HTTP services, SRV records can specify ports:

_http._tcp.mywebapp.mydomain. 3600 IN SRV 10 5 10000 myserver.mydomain.

Note: Most web browsers don't support SRV record resolution for HTTP/HTTPS.

• Reverse proxies provide additional benefits like load balancing and SSL termination
• Port forwarding at network level may bypass application security layers
• Monitor connection limits when using simple redirects