Edge computing promises low latency and global distribution. But running code at the edge has constraints that trip up developers. Here's when edge functions shine and when to avoid them.
Edge Runtime Constraints
Limited Node.js APIs—no fs, limited crypto, no native modules. Connection pool challenges—can't maintain persistent DB connections. Cold starts still exist, though typically faster. Size limits on code bundles.
Perfect Use Cases
Authentication checks: Verify tokens before requests reach your origin.
Personalization: Customize responses based on geolocation, cookies, or headers.
A/B testing: Route users to variants without origin round-trips.
Redirects and rewrites: Handle URL transformations globally.
// Edge middleware for A/B testing
export function middleware(request) {
const bucket = request.cookies.get('ab-bucket') || Math.random() < 0.5 ? 'A' : 'B';
const url = request.nextUrl.clone();
url.pathname = \`/\${bucket}\${url.pathname}\`;
const response = NextResponse.rewrite(url);
response.cookies.set('ab-bucket', bucket);
return response;
}Anti-Patterns
Database-heavy operations—edge to database latency often negates edge benefits. Heavy computation—edge has limited CPU time. Large response generation—streaming from origin may be better.
Platform Comparison
Vercel Edge: Tight Next.js integration, automatic deployment. Cloudflare Workers: More features (KV, D1, R2), larger ecosystem. Deno Deploy: TypeScript-first, web standard APIs.
Hybrid Architecture
Best pattern: edge for routing, personalization, and caching decisions. Origin for data operations and heavy computation.
// Edge decides, origin executes
export async function middleware(request) {
// Fast checks at edge
if (!isAuthenticated(request)) {
return NextResponse.redirect('/login');
}
// Pass through to origin for data-heavy work
return NextResponse.next();
}Edge functions are a powerful tool, but not a silver bullet. Use them where they shine: low-latency decisions close to users.