Edge Functions

Edge functions run at the CDN's POPs, geographically near the user — typically with cold-start measured in milliseconds and execution measured in microseconds. They sit inside the CDN itself, intercepting requests before they ever reach your origin.

Why Edge?

Edge functions are also vastly cheaper per invocation than container-based serverless. Pricing is typically per million requests, often with generous free tiers.

The Players

Cloudflare Workers and Vercel Edge Functions are the two most common starting points. Fastly Compute@Edge is heavier-duty (WASM) but faster. Deno Deploy is the strong Web-standard alternative.

The Programming Model

Edge functions are HTTP-shaped: a request comes in, you return a response. The platforms standardize on Web standard APIs — Request, Response, fetch — not Node.js-specific APIs.

// Same code runs on Cloudflare Workers, Deno Deploy, Vercel Edge,
// Netlify Edge Functions, and the browser
export default {
  async fetch(request, env, ctx) {
    const url = new URL(request.url);
    if (url.pathname === '/health') {
      return new Response('ok');
    }
    return fetch(request);   // pass through to origin
  },
};

The catch: no fs, no crypto.createHash (use Web Crypto), no Express middleware, no long-running processes. You're closer to the browser's JS environment than to Node.js.

When Edge Wins

When Edge Loses

A common architecture: edge handles the request shape (routing, auth, simple personalization, transforms), your origin handles business logic and data access.

Learning Path

Edge vs Other Compute Platforms

They compose. An app commonly has edge functions in front of (or in tandem with) a container backend in front of a database.