Does Fastify Work With Vercel?
Fastify can run on Vercel using Serverless Functions, but it requires adaptation since Vercel's runtime model doesn't align perfectly with Fastify's server-based architecture.
Quick Facts
How Fastify Works With Vercel
Fastify is a traditional Node.js web server framework designed to run as a long-lived process, while Vercel's primary deployment model uses stateless serverless functions that handle individual HTTP requests. This fundamental mismatch means you can't deploy a standard Fastify application directly to Vercel. However, there are two practical approaches: (1) Use Vercel's serverless functions to wrap individual Fastify route handlers, which defeats most of Fastify's performance benefits, or (2) Deploy Fastify to Vercel's native Node.js support via a monorepo structure where the API folder contains an Express/Node.js compatible setup. The most practical solution is using `@fastify/serverless` or adapting Fastify handlers to work with Vercel's `/api` routes pattern. Alternatively, deploy Fastify to traditional Node.js hosting (Railway, Heroku, AWS EC2) and consume it from a Vercel frontend. This separation actually provides better scalability since your API and frontend can scale independently.
Best Use Cases
Fastify with Vercel - Best Practice Pattern
npm install fastify// backend/index.js - Deploy to Railway/Heroku, NOT Vercel
const fastify = require('fastify')({ logger: true });
fastify.get('/api/health', async (request, reply) => {
return { status: 'ok' };
});
fastify.post('/api/data', async (request, reply) => {
const { name } = request.body;
return { received: name, timestamp: new Date() };
});
const start = async () => {
try {
await fastify.listen({ port: 3001, host: '0.0.0.0' });
} catch (err) {
fastify.log.error(err);
process.exit(1);
}
};
start();
// frontend - Deploy to Vercel
// fetch('https://your-fastify-backend.com/api/data', { method: 'POST', body: JSON.stringify({name: 'test'}) })Known Issues & Gotchas
Fastify's server model (persistent connection) incompatible with Vercel's stateless functions
Fix: Don't try to run a full Fastify instance on Vercel. Instead, use Vercel for frontend and deploy Fastify elsewhere, or refactor to use Vercel's native Node.js API routes
Cold starts with serverless wrappers eliminate Fastify's low-overhead advantage
Fix: If you need Fastify's performance, deploy to traditional Node.js hosting. Vercel serverless adds 0.5-2s overhead per request due to function initialization
WebSocket support requires Vercel Pro and additional configuration, Fastify's streaming is limited
Fix: Use REST or gRPC instead of WebSockets on Vercel, or host Fastify on a platform with WebSocket support
Environment variables and secrets management differs between Fastify local dev and Vercel deployment
Fix: Use `.env.local` for development, configure secrets in Vercel dashboard, and validate at startup
Alternatives
- •Express.js with Vercel Serverless Functions - native support via @vercel/node
- •Next.js API Routes on Vercel - seamless integration, built for serverless
- •AWS Lambda with Fastify - better cold start performance than Vercel, full server control
Resources
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