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Edge Functions

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Filed underBackendApisInfrastructurePerformance

In brief · quick answer

Edge functions are serverless functions that run at the network edge, in CDN nodes geographically close to users, rather than in a single centralized region. They minimize latency by executing code as close to the user as possible.

§ 1 Definition

Edge functions extend the serverless model to the network edge. Instead of running code in one AWS region (us-east-1, eu-west-1), edge functions run in hundreds of global locations, each within the CDN nodes that serve your static assets. When a user in Tokyo requests your API, an edge function runs in a Tokyo node, not a Virginia data center. This eliminates the round-trip across the planet and reduces latency from hundreds of milliseconds to single digits. Edge functions are built on WebAssembly (Wasm) or lightweight JavaScript runtimes optimized for fast cold starts. Cloudflare Workers, Deno Deploy, Vercel Edge Functions, and Netlify Edge Functions are the primary platforms. Edge functions are constrained compared to full serverless: smaller memory limits (typically 128MB vs 10GB), no filesystem access, limited runtime APIs, and no native Node.js modules. They excel at lightweight request handling: authentication checks, A/B testing, redirects, header manipulation, and API gateway logic.

§ 2 Edge vs Region Serverless

The key difference is location. Region serverless functions (AWS Lambda) run in a single data center. Edge functions run in hundreds of CDN nodes globally. This makes edge functions ideal for latency-sensitive operations: authentication checks, geolocation-based routing, personalization, A/B testing, and static asset manipulation. Edge functions are not suitable for heavy computation, database queries (unless the database is also at the edge), or long-running processes. The edge runtime is intentionally constrained for speed. A common architecture is edge functions for the request layer (auth, routing, caching) passing to region functions for business logic and data access. Vercel's runtime model supports this 'edge + serverless' hybrid pattern.

§ 3 Edge Runtimes and Constraints

Edge functions run on specialized lightweight runtimes. Cloudflare Workers use the Service Worker API with V8 isolates (not containers), achieving sub-millisecond cold starts. Vercel Edge Functions use the Edge Runtime based on V8. Deno Deploy uses the Deno runtime at the edge. Common constraints include: no filesystem reads, no Node.js built-in modules (fs, net, http), limited memory (128MB), limited CPU time per request, and a restricted set of APIs (Web standard APIs like Request, Response, fetch, crypto, URL, TextEncoder). These constraints push edge functions toward middleware-style logic rather than full application backends. For anything requiring database access, file storage, or complex computation, use region serverless or a traditional server.

§ 4 When to Use Edge Functions

Edge functions are optimal for operations that must happen before a request reaches your main application. Authentication and authorization checks redirect unauthenticated users instantly. Geolocation-based routing sends visitors to the right regional site. A/B testing splits traffic at the edge without JavaScript. Bot detection blocks malicious traffic before it hits your origin. Redirects and rewrites (301, 308) at CDN speed. URL normalization and headers manipulation. Personalization (read a cookie, customize the response). Static asset optimization and manipulation. If your logic can be expressed as 'look at the request, make a decision, respond or forward,' it is a candidate for edge functions.

§ 5 Note

Common misunderstanding: Edge functions are not just faster serverless functions. They run in a fundamentally different runtime with different constraints. Edge functions are for lightweight request-layer logic, not for running your full application. Another misconception: edge functions eliminate cold starts entirely. Cloudflare Workers (V8 isolates) have near-zero cold starts, but Vercel Edge Functions can experience cold starts, though they are faster than region serverless. Also: edge functions are not a replacement for serverless functions. They complement each other. Use edge for the request layer, region serverless for the application layer.

§ 6 In code

```javascript
// Cloudflare Workers edge function
// Runs in 300+ locations worldwide

export default {
  async fetch(request, env, ctx) {
    const url = new URL(request.url);
    const country = request.cf?.country;
    
    // Redirect based on geolocation
    if (country === 'DE' && url.pathname === '/') {
      return Response.redirect('https://de.example.com', 302);
    }
    
    // Authentication check at the edge
    const authHeader = request.headers.get('Authorization');
    if (url.pathname.startsWith('/api/') && !authHeader) {
      return new Response('Unauthorized', { status: 401 });
    }
    
    // Forward to origin
    return fetch(request);
  }
};
```

§ 7 Common questions

Q. Do edge functions support databases?: A. They can connect to databases, but each connection adds latency. For best results, use databases at the edge (D1, PlanetScale, or Neon) or limit edge functions to auth/cache logic, passing data queries to region functions.
Q. Are edge functions expensive?: A. Most providers offer generous free tiers. Cloudflare Workers has 100K requests/day free. Vercel includes 100K edge function invocations/month on the Hobby plan. Pricing is per-invocation plus duration, similar to serverless.
Q. Can I run any npm package in an edge function?: A. No. Edge runtimes support only Web-standard APIs and a subset of Node.js APIs. Packages that use fs, net, or native modules will not work. Check compatibility before choosing edge functions.

Key takeaways

Edge functions run in CDN nodes globally, minimizing latency to single digits.
Best for lightweight request-layer logic: auth, redirects, A/B testing, personalization.
Edge runtimes are constrained (128MB, no fs, no Node.js built-ins) by design.
Edge functions complement region serverless; use edge for the request layer, not the application layer.

How Atomic Glue helps

Atomic Glue uses edge functions for latency-critical operations like authentication, redirects, and A/B testing. On projects hosted with Vercel or Cloudflare, we move as much request-layer logic to the edge as possible, reserving region functions and traditional servers for database access and business logic. This hybrid architecture gives users sub-100ms response times globally. Edge computing is a key optimization pattern in our Web Development services. Get in touch to optimize your application's global performance.

Get in touch

# Edge Functions

Category: Backend (also: Apis, Infrastructure, Performance)

Author: Atomic Glue Development Team

## Definition

## Edge vs Region Serverless

## Edge Runtimes and Constraints

## When to Use Edge Functions

## Note

## In code

## Common questions
Q: Do edge functions support databases?
A: They can connect to databases, but each connection adds latency. For best results, use databases at the edge (D1, PlanetScale, or Neon) or limit edge functions to auth/cache logic, passing data queries to region functions.
Q: Are edge functions expensive?
A: Most providers offer generous free tiers. Cloudflare Workers has 100K requests/day free. Vercel includes 100K edge function invocations/month on the Hobby plan. Pricing is per-invocation plus duration, similar to serverless.
Q: Can I run any npm package in an edge function?
A: No. Edge runtimes support only Web-standard APIs and a subset of Node.js APIs. Packages that use fs, net, or native modules will not work. Check compatibility before choosing edge functions.

## Key takeaways

Edge functions run in CDN nodes globally, minimizing latency to single digits.
Best for lightweight request-layer logic: auth, redirects, A/B testing, personalization.
Edge runtimes are constrained (128MB, no fs, no Node.js built-ins) by design.
Edge functions complement region serverless; use edge for the request layer, not the application layer.

## Related entries

Last updated June 2026. Permalink: atomicglue.co/glossary/edge-functions