Edge Runtime Limitations in Next.js
Your middleware worked perfectly in development. In production on Edge, fs.readFile throws, Prisma fails to connect, and a 2MB dependency blows past the bundle limit. Edge Runtime trades Node.js compatibility for global low-latency deployment—but only some workloads fit.
('Choosing Edge vs Node runtime', "Export runtime = 'edge' only when you have measured latency win and confirmed dependency compatibility.\n\ntypescript\nexport const runtime = 'edge';\n\nexport async function GET() {\n const country = request.headers.get('x-vercel-ip-country') ?? 'US';\n return Response.json({ country });\n}\n\n\nDefault to Node.js runtime until profiling proves Edge benefit.")
('Bundle size constraints', 'Edge functions ship as bundled JavaScript with strict size limits (typically 1–4MB depending on platform). ORMs, PDF libraries, and image processing libraries exceed limits quickly.\n\nPattern: Edge validates JWT and routes; Node handler processes business logic via internal fetch.')
('Database and ORM pitfalls', 'Prisma, pg, mysql2 use Node TCP sockets unavailable on Edge. Use HTTP-based data APIs: Prisma Accelerate, PlanetScale serverless driver, Supabase REST, or your own Node API.\n\nNever import PrismaClient in edge middleware—it fails at build or runtime.')
('Cold starts and latency', 'Edge cold starts are faster than Node serverless but still exist. Keep handler logic minimal. Avoid top-level await of heavy initialization.\n\nWarm critical paths with scheduled pings only if your platform charges for invocations—often unnecessary on Vercel Edge.')
('Web Crypto vs Node crypto', "Use Web Crypto API for JWT verification on Edge:\n\ntypescript\nimport { jwtVerify } from 'jose';\n\nconst { payload } = await jwtVerify(token, secret);\n\n\njsonwebtoken depends on Node crypto—replace with jose for Edge compatibility.")
('Production decision matrix', '| Use case | Runtime |\n|----------|--------|\n| Geo redirect | Edge |\n| JWT gate | Edge |\n| Stripe webhook | Node |\n| PDF generation | Node |\n| RSC data fetch with ORM | Node |')
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Production notes on edge runtime limitations
Ship incrementally with rollback paths. Measure p95 latency and error rate before and after changes. Document trade-offs in ADRs so on-call understands why the current design exists.
Frequently asked questions
What APIs are unavailable on Edge Runtime?
Node.js core modules like fs, crypto.createHash (limited), child_process, and native addons. Use Web APIs: fetch, Web Crypto, TextEncoder. Database drivers needing TCP often fail.
Should Route Handlers use Edge by default?
Only for lightweight auth checks, geo routing, A/B assignment, and proxying. Data mutations and ORM access belong on Node.js runtime.
How do I debug Edge bundle size errors?
Run next build and inspect .next/server/edge chunks. Use @vercel/nft or bundle analyzer. Split heavy logic to Node Route Handlers called from Edge.
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