Edge Functions

Edge functions are small pieces of server-side code that run at locations distributed around the world, close to the user making the request. Instead of routing every request back to a single origin server in one geographic location, edge functions execute at the nearest available infrastructure node, which can be a few milliseconds away from the user rather than hundreds of milliseconds.

Common use cases include rewriting URLs before they reach the origin, personalizing responses based on geographic location or cookies, authenticating requests without a round trip to a centralized server, running A/B tests at the routing layer, and handling redirects at scale. Because edge functions execute before reaching the origin, they can also block bad traffic, rate-limit requests, or add security headers without touching the application server.

The main platforms offering edge function capabilities are Vercel Edge Functions, Cloudflare Workers, AWS Lambda@Edge, and Netlify Edge Functions. Each has its own runtime constraints. Most run in a restricted environment that excludes Node.js-specific APIs and limits execution time, which makes them unsuitable for heavy computation but well-suited for lightweight routing and transformation logic.

The tradeoff to understand is that edge functions add infrastructure complexity. Debugging distributed code is harder than debugging a single server, and cold start times, while usually short, do exist. They work best as a targeted tool for specific latency-sensitive problems rather than a default approach for all server logic.