Cloudflare Workers for Edge Performance

Cloudflare Workers execute JavaScript at 300+ edge locations worldwide, bringing your server logic within milliseconds of every user. This can reduce TTFB from 200-500ms to under 20ms.

What Are Cloudflare Workers?

Workers are serverless functions that run at the edge — not in a centralized data center, but at the Cloudflare PoP (Point of Presence) closest to each user.

// A basic Worker
export default {
  async fetch(request) {
    return new Response('Hello from the edge!', {
      headers: { 'content-type': 'text/html' },
    });
  },
};

Edge vs. Serverless vs. Traditional

Architecture	TTFB (US user, US server)	TTFB (EU user, US server)
Traditional server	50-100ms	200-400ms
Serverless (Lambda)	100-500ms (cold start)	200-600ms
Cloudflare Worker	5-20ms	5-20ms

Performance Use Cases

1. Edge-Side HTML Rendering

Generate pages at the edge instead of your origin:

export default {
  async fetch(request) {
    const url = new URL(request.url);
    
    if (url.pathname === '/') {
      return new Response(renderHomepage(), {
        headers: {
          'content-type': 'text/html',
          'cache-control': 'public, max-age=3600',
        },
      });
    }
    
    // Fall through to origin for other paths
    return fetch(request);
  },
};

2. Smart Caching and Rewriting

export default {
  async fetch(request) {
    const cache = caches.default;
    let response = await cache.match(request);
    
    if (!response) {
      response = await fetch(request);
      
      // Cache successful responses for 1 hour
      if (response.ok) {
        response = new Response(response.body, response);
        response.headers.set('cache-control', 'public, max-age=3600');
        await cache.put(request, response.clone());
      }
    }
    
    return response;
  },
};

3. Image Optimization at the Edge

export default {
  async fetch(request) {
    const url = new URL(request.url);
    
    if (url.pathname.startsWith('/images/')) {
      // Use Cloudflare Image Resizing
      return fetch(request, {
        cf: {
          image: {
            width: 800,
            quality: 75,
            format: 'avif',
          },
        },
      });
    }
    
    return fetch(request);
  },
};

4. A/B Testing Without Client-Side JavaScript

export default {
  async fetch(request) {
    const url = new URL(request.url);
    
    // Determine variant from cookie or randomly assign
    const cookie = request.headers.get('cookie') || '';
    let variant = cookie.includes('ab=B') ? 'B' : 
                  cookie.includes('ab=A') ? 'A' :
                  Math.random() < 0.5 ? 'A' : 'B';
    
    // Rewrite to variant page
    url.pathname = `/variants/${variant}${url.pathname}`;
    const response = await fetch(url.toString());
    
    // Set cookie for consistency
    const newResponse = new Response(response.body, response);
    if (!cookie.includes('ab=')) {
      newResponse.headers.set('set-cookie', `ab=${variant}; path=/; max-age=86400`);
    }
    
    return newResponse;
  },
};

5. Bot Detection and Security

export default {
  async fetch(request) {
    const userAgent = request.headers.get('user-agent') || '';
    
    // Block known bad bots
    if (/BadBot|Scraper/i.test(userAgent)) {
      return new Response('Blocked', { status: 403 });
    }
    
    // Add security headers
    const response = await fetch(request);
    const secured = new Response(response.body, response);
    secured.headers.set('X-Frame-Options', 'DENY');
    secured.headers.set('X-Content-Type-Options', 'nosniff');
    
    return secured;
  },
};

Workers KV for Edge Data

Store data at the edge for sub-millisecond reads:

export default {
  async fetch(request, env) {
    const config = await env.CONFIG_KV.get('site-config', 'json');
    
    return new Response(renderPage(config), {
      headers: { 'content-type': 'text/html' },
    });
  },
};

Performance Impact

Before Workers	After Workers	Improvement
TTFB: 300ms	TTFB: 15ms	95% faster
Global variance: 100-500ms	Global variance: 10-25ms	Consistent worldwide
Origin requests: 100%	Origin requests: 10-20%	80% reduction

Monitor Your Edge Performance

Edge functions add a layer between users and your origin. Monitor both to ensure optimal performance.

Monitor your edge performance →

Related Reading

• Core web vitals 2026 complete guide
• How to prioritize performance fixes impact matrix
• Speed optimization roadmap 30 60 90