Cloudflare Worker: Subdomain-Based Language Routing for chen.ist

This document describes how to set up subdomain-based language routing so that:

chen.ist serves English content (root /)
ro.chen.ist serves Romanian content from /ro/*
de.chen.ist serves German content from /de/*
se.chen.ist serves Swedish content from /sv/*

The site is hosted on GitHub Pages at chenist-co.github.io with custom domain chen.ist.

1. Cloudflare Worker Script

Create a Worker named lang-router with the following script:

/**
 * Cloudflare Worker: Subdomain-based language routing for chen.ist
 *
 * Routes language subdomains to the corresponding path prefix on the origin.
 *   ro.chen.ist  ->  chen.ist/ro/
 *   de.chen.ist  ->  chen.ist/de/
 *   se.chen.ist  ->  chen.ist/sv/   (Swedish subdomain uses /sv/ path)
 *
 * All other requests (including chen.ist itself) pass through unchanged.
 */

const SUBDOMAIN_TO_PATH = {
  'ro': '/ro',
  'de': '/de',
  'se': '/sv',
};

const ORIGIN = 'https://chen.ist';

addEventListener('fetch', (event) => {
  event.respondWith(handleRequest(event.request));
});

async function handleRequest(request) {
  const url = new URL(request.url);
  const hostname = url.hostname;

  // Extract subdomain: "ro.chen.ist" -> "ro"
  const parts = hostname.split('.');
  let subdomain = null;

  if (parts.length === 3 && parts[1] === 'chen' && parts[2] === 'ist') {
    subdomain = parts[0];
  }

  // If no language subdomain match, pass through unchanged
  const pathPrefix = subdomain ? SUBDOMAIN_TO_PATH[subdomain] : null;
  if (!pathPrefix) {
    return fetch(request);
  }

  // Build the rewritten URL
  // e.g., ro.chen.ist/services.html -> chen.ist/ro/services.html
  let path = url.pathname;

  // Prevent double-prefixing if someone visits ro.chen.ist/ro/something
  if (path.startsWith(pathPrefix + '/') || path === pathPrefix) {
    return fetch(request);
  }

  // Append path prefix to the origin
  const newPath = pathPrefix + (path === '/' ? '/index.html' : path);
  const originUrl = new URL(newPath, ORIGIN);
  originUrl.search = url.search;

  // Fetch from origin with the rewritten URL
  const originRequest = new Request(originUrl.toString(), {
    method: request.method,
    headers: request.headers,
    redirect: 'follow',
  });

  let response = await fetch(originRequest, {
    cf: {
      // Cache on Cloudflare edge
      cacheTtl: 300,
      cacheEverything: true,
    },
  });

  // If the direct path fails, try appending /index.html for directory URLs
  if (response.status === 404 && !path.includes('.') && !path.endsWith('/')) {
    const dirUrl = new URL(pathPrefix + path + '/index.html', ORIGIN);
    dirUrl.search = url.search;

    const dirRequest = new Request(dirUrl.toString(), {
      method: request.method,
      headers: request.headers,
      redirect: 'follow',
    });

    const dirResponse = await fetch(dirRequest, {
      cf: { cacheTtl: 300, cacheEverything: true },
    });

    if (dirResponse.status === 200) {
      response = dirResponse;
    }
  }

  // Clone response and set headers for proper caching and CORS
  const newResponse = new Response(response.body, response);

  // Add canonical hint so search engines know the relationship
  if (response.status === 200) {
    newResponse.headers.set('X-Robots-Tag', 'noindex');
    // Optional: if you want search engines to index subdomains instead,
    // remove the line above and handle canonical tags in your HTML.
  }

  return newResponse;
}

Note on X-Robots-Tag: The script sets X-Robots-Tag: noindex on subdomain responses by default to avoid duplicate content issues with search engines (since the same content exists at both chen.ist/ro/ and ro.chen.ist/). Remove this header if you want subdomains to be indexed instead and plan to add proper <link rel="canonical"> tags in your HTML.

2. DNS Setup (Cloudflare Dashboard)

Go to Cloudflare Dashboard > chen.ist > DNS > Records and add these CNAME records:

Type	Name	Target	Proxy status
CNAME	`ro`	`chen.ist`	Proxied
CNAME	`de`	`chen.ist`	Proxied
CNAME	`se`	`chen.ist`	Proxied

Important: All three records must be set to Proxied (orange cloud icon), not DNS-only. The Worker only runs on proxied traffic.

The existing DNS records for chen.ist itself (pointing to GitHub Pages) should remain unchanged.

Verify DNS records

After adding, your DNS records should include at minimum:

chen.ist        CNAME   chenist-co.github.io    Proxied
ro.chen.ist     CNAME   chen.ist                Proxied
de.chen.ist     CNAME   chen.ist                Proxied
se.chen.ist     CNAME   chen.ist                Proxied

3. Create the Worker (Cloudflare Dashboard)

Step 1: Navigate to Workers

Log in to the Cloudflare Dashboard.
Select the chen.ist domain from your account.
In the left sidebar, click Workers & Pages.
Click Create.
Select “Create Worker”.

Step 2: Configure the Worker

Name the Worker: lang-router
Click Deploy to create it with the default “Hello World” code.
After deployment, click Edit Code.
Replace the entire contents with the Worker script from Section 1 above.
Click Save and Deploy.

Step 3: Alternatively, deploy via Wrangler CLI

If you prefer the command line:

# Install Wrangler if not already installed
npm install -g wrangler

# Authenticate
wrangler login

# Create the project directory
mkdir -p cloudflare-worker && cd cloudflare-worker

# Create wrangler.toml
cat > wrangler.toml << 'EOF'
name = "lang-router"
main = "worker.js"
compatibility_date = "2024-01-01"

# Routes are configured per-zone
# These tell Cloudflare which requests should trigger this Worker
[[routes]]
pattern = "ro.chen.ist/*"
zone_name = "chen.ist"

[[routes]]
pattern = "de.chen.ist/*"
zone_name = "chen.ist"

[[routes]]
pattern = "se.chen.ist/*"
zone_name = "chen.ist"
EOF

# Save the Worker script as worker.js (copy from Section 1)
# Then deploy:
wrangler deploy

4. Worker Route Configuration

If you created the Worker through the dashboard (not Wrangler), you need to add routes manually.

Add routes via Dashboard

Go to Cloudflare Dashboard > chen.ist > Workers Routes.
Click Add Route and create these three routes:

Route Pattern	Worker
`ro.chen.ist/*`	`lang-router`
`de.chen.ist/*`	`lang-router`
`se.chen.ist/*`	`lang-router`

Do not add a route for chen.ist/* – the main domain should continue to serve directly from GitHub Pages without Worker intervention.

Alternatively, add routes via API

# Get your Zone ID from the dashboard Overview page
ZONE_ID="your-zone-id"
API_TOKEN="your-api-token"
WORKER_NAME="lang-router"

for pattern in "ro.chen.ist/*" "de.chen.ist/*" "se.chen.ist/*"; do
  curl -X POST "https://api.cloudflare.com/client/v4/zones/$ZONE_ID/workers/routes" \
    -H "Authorization: Bearer $API_TOKEN" \
    -H "Content-Type: application/json" \
    --data "{\"pattern\": \"$pattern\", \"script\": \"$WORKER_NAME\"}"
done

5. Testing

Quick smoke test with curl

# Test Romanian subdomain
curl -sI https://ro.chen.ist/ | head -20

# Test that content comes from /ro/ path
curl -s https://ro.chen.ist/ | grep -i "<title>"

# Test German subdomain
curl -sI https://de.chen.ist/ | head -20

# Test Swedish subdomain
curl -sI https://se.chen.ist/ | head -20

# Test a subpage
curl -sI https://ro.chen.ist/services.html

# Test that the main domain still works
curl -sI https://chen.ist/ | head -20

# Verify query strings are preserved
curl -sI "https://ro.chen.ist/services.html?ref=test"

What to verify

Status codes: All subdomain requests should return 200 OK.
Content correctness: ro.chen.ist/ should return the same content as chen.ist/ro/index.html.
Subpages: de.chen.ist/services.html should match chen.ist/de/services.html.
Main domain: chen.ist should be unaffected and serve English content.
Query strings: se.chen.ist/page?foo=bar should forward the query string.
Assets: CSS, JS, and images should load correctly (check browser console for errors).

Browser testing

Open https://ro.chen.ist in your browser.
Open DevTools (F12) and check the Network tab for any failed requests.
Verify that navigation links within the site work correctly.
Check that all CSS/JS/images load properly.

Common issues

Symptom	Cause	Fix
`522` or `523` error	DNS record not proxied	Set CNAME to Proxied (orange cloud)
`404` on subdomain	Worker route not configured	Add the route in Workers Routes
Redirect loop	GitHub Pages redirecting	Ensure CNAME file only contains `chen.ist`
Mixed content	Assets loaded over HTTP	Ensure all asset URLs are relative or protocol-relative
CSS/JS missing	Assets reference absolute paths to `chen.ist`	Use relative paths in your HTML templates

6. Optional: Asset Handling

If your site uses absolute URLs for CSS, JS, or images (e.g., /assets/style.css), these will work correctly because the Worker only rewrites paths on the language subdomains and assets typically live at the root level.

However, if language-specific pages reference assets with language-prefixed paths (e.g., /ro/assets/style.css), the Worker will correctly route these since it prepends the language path prefix to all requests on that subdomain.

Relative links between pages

Internal links in your language pages should use relative paths. For example, in /ro/services.html, a link to the contact page should be:

<!-- On ro.chen.ist, this works as-is -->
<a href="contact.html">Contact</a>

<!-- Avoid absolute paths that include the language prefix -->
<!-- This would break: <a href="/ro/contact.html"> -->

If your Quarto site generates absolute paths with the language prefix, the Worker handles this correctly because it passes through requests that already have the prefix (the double-prefix guard in the script).

7. GitHub Pages Configuration

No changes are needed to your GitHub Pages setup. The existing CNAME file should remain as-is with chen.ist only. GitHub Pages does not need to know about the subdomains because Cloudflare’s Worker handles the routing before the request reaches GitHub Pages.

Your current CNAME file:

chen.ist

This is correct. Do not add subdomains to this file.