Edge Functions: Running Code at the CDN Layer

Edge Functions represent a fundamental shift in deployment architecture, allowing developers to run code at CDN edge locations closest to users. Instead of routing all requests to a central origin server, you deploy functions to hundreds of global locations. The result is dramatically reduced latency—function execution happens milliseconds from the user rather than across continents. Edge Functions are ideal for use cases like A/B testing (split traffic before serving HTML), authentication (check cookies and redirect before origin hits), geolocation-based routing, bot detection, and API rate limiting. Providers like Vercel Edge Functions, Cloudflare Workers, and Netlify Edge Functions all use the V8 isolate technology, providing fast cold starts and consistent performance. The programming model is similar to serverless functions but with constraints—you're limited in execution time (typically under 50ms for synchronous functions) and available APIs. Edge Functions can't run heavy compute workloads, but they excel at request/response manipulation. Implementation patterns include using edge middleware to authenticate users, rewriting URLs for localization, or fetching data from multiple APIs and streaming responses. The cost model is generous at scale, and the performance benefits are measurable. Start by moving simple request transformations to the edge—you'll likely find more opportunities once you experience the latency improvements.