Yes, you can absolutely create purely numeric subdomains like 2009.example.com. The DNS specification (RFC 1035) permits subdomains containing:

• Digits (0-9)
• Letters (a-z, case insensitive)
• Hyphens (except as first/last character)

Here's how to implement numeric subdomains across common platforms:

DNS Configuration (BIND Example)

; zone file snippet
2009    IN  A       192.0.2.1
2023    IN  CNAME   main.example.com.

Apache Virtual Host

<VirtualHost *:80>
    ServerName 2009.example.com
    DocumentRoot /var/www/2009
    <Directory /var/www/2009>
        Require all granted
    </Directory>
</VirtualHost>

Nginx Configuration

server {
    listen 80;
    server_name 2009.example.com;
    root /var/www/2009;
    index index.html;
}

While technically valid, consider these practical aspects:

1. Cookie Security Considerations

Some browsers may treat numeric domains differently for cookie handling. Test with:

document.cookie = "test=value; domain=.example.com; path=/";

2. SSL Certificate Validation

Wildcard certificates will work, but some CA validation systems might flag numeric-only domains during issuance.

3. Application Framework Routing

Some frameworks may interpret numeric subdomains as IDs. For Express.js:

app.param('year', (req, res, next, id) => {
    if (/^\d+$/.test(id)) {
        req.year = parseInt(id);
        return next();
    }
    next(new Error('Invalid numeric subdomain')); 
});

Search engines treat numeric subdomains like any other subdomain. However, consider these best practices:

• Implement proper 301 redirects if changing existing URLs
• Ensure the numeric value has semantic meaning (e.g., versioning, years)
• Include metadata in your HTML head:

<link rel="canonical" href="https://2009.example.com" />
<meta property="og:url" content="https://2009.example.com" />

Numeric subdomains are particularly useful for:

// API versioning
https://v1.api.example.com
https://2023.api.example.com

// Multi-tenant SaaS applications
https://12345.crm.example.com  // Where 12345 is tenant ID

// Temporal content archives
https://1999.archive.example.com

For programmatic subdomain creation, here's a Node.js example:

const dns = require('dns');
const util = require('util');

async function checkSubdomain(sub) {
    try {
        const lookup = util.promisify(dns.lookup);
        await lookup(${sub}.example.com);
        return true;
    } catch (err) {
        return false;
    }
}

Yes, you can absolutely create purely numeric subdomains like 2009.example.com. According to RFC 1035, DNS labels can contain:

• Alphanumeric characters (a-z, 0-9)
• Hyphens (except as first/last character)
• Length between 1-63 characters

Many major services use numeric subdomains:

# GitHub Pages
2001.example.github.io

# Cloudflare workers
1234.workers.dev

# API versioning
api.v2.example.com

Here's how to set this up in various systems:

DNS Zone File Example

; BIND zone file example
$ORIGIN example.com.
2009     IN  A     192.0.2.1
2023     IN  CNAME example.com.

Cloudflare API Example

# Using curl to create numeric subdomain
curl -X POST "https://api.cloudflare.com/client/v4/zones/ZONE_ID/dns_records" \
-H "Authorization: Bearer API_TOKEN" \
-H "Content-Type: application/json" \
--data '{"type":"A","name":"2009","content":"192.0.2.1","ttl":3600}'

Watch out for:

• Some legacy systems may treat numeric-only domains as IP addresses
• Regex validation in older applications might reject pure numbers
• SSL certificates may require special handling (wildcards won't cover numeric subdomains)

Use these commands to verify:

# DNS lookup
dig 2009.example.com +short

# HTTP test
curl -I http://2009.example.com

# SSL verification
openssl s_client -connect 2009.example.com:443 -servername 2009.example.com

When handling numeric subdomains in code:

// JavaScript URL validation example
function isValidSubdomain(sub) {
    return /^(?!-)[a-z0-9-]{1,63}(?