# Advanced: Vercel Edge Functions, Analytics & Team Workflows

Edge Functions: Code at the CDN Edge

Standard serverless functions run in a single region (usually us-east-1). Edge Functions run globally — on the CDN node closest to each user. This means sub-50ms response times worldwide.

// app/api/geo/route.ts
export const runtime = 'edge'; // This is the key line

export async function GET(request: Request) {
  // Vercel injects geo data at the edge
  const country = request.headers.get('x-vercel-ip-country') || 'US';
  const city = request.headers.get('x-vercel-ip-city') || 'Unknown';

  return Response.json({
    greeting: `Hello from ${city}, ${country}!`,
    timestamp: Date.now(),
  });
}

When to use Edge vs. Node.js runtime: - Edge: Authentication checks, geo-routing, personalization, A/B testing, simple API responses - Node.js: Database queries (most DB clients need Node.js), file system access, heavy computation, packages that use Node.js APIs

Edge limitations: No fs module, no native Node.js modules, 128KB code size limit after compression, limited NPM package compatibility. The edge runtime uses V8 isolates (like Cloudflare Workers), not full Node.js.