How to ship an Elysia app on Vercel

Elysia is an ergonomic web framework for building backend servers with TypeScript. Designed with simplicity and type safety in mind, it offers a familiar chained API, end-to-end type inference, and built-in support for validation, lifecycle hooks, and response streaming. Elysia is optimized for Bun, and it also runs on Node.js.

On Vercel, you can deploy an Elysia app with zero configuration: your routes become Vercel Functions running on Fluid compute, and you get response streaming, preview deployments, and observability without extra setup.

This guide walks you through deploying an Elysia app to Vercel from a template, the Vercel CLI, or a Git repository, then configuring features such as streaming, lifecycle hooks, cron jobs, the Bun runtime, and observability.

Before you begin, make sure you have:

• A Vercel account
• Node.js 20+ and a package manager (e.g., npm)
• An existing Elysia project, or a new one created from the Elysia on Vercel template
• A Git repository on GitHub, GitLab, or Bitbucket (if you want Git-based deployments)
• Vercel CLI installed (npm i -g vercel)

When you deploy an Elysia app, Vercel detects the framework and builds it for the Vercel runtime. Your exported Elysia app handles requests through Vercel Functions, which run on Fluid compute by default. Your app scales with traffic, and you pay only for the compute your functions use, not for idle time.

Because Vercel ships zero-configuration detection for Elysia, you don't set a build command or output directory. Vercel reads your project, finds the file that exports your Elysia app, and applies the correct build settings.

You can ship an Elysia app to Vercel in three ways. Choose the one that fits where your code lives today.

The fastest way to ship an Elysia app is to start from the Elysia on Vercel template, a minimal Elysia API that deploys with zero configuration. When you deploy it, Vercel clones the template to your Git provider, creates a project, and deploys it.

To scaffold a new Elysia project locally, use the Vercel CLI init command. It clones Vercel's Elysia example into a folder named elysia.

1. Create the project:
   Terminal

   vercel init elysia

2. Install dependencies:
   Terminal

   cd elysia
   npm install

3. Develop locally at http://localhost:3000. Use the Vercel CLI, so your app runs with the same default export it uses in production:
   Terminal

   vercel dev

4. Create a preview deployment. The first run creates a Vercel project link:
   Terminal

   vercel

5. Promote your deployment to production:
   Terminal

   vercel --prod

If you already have an Elysia app, deploy it from Git or from the command line.

From Git: Push your project to GitHub, GitLab, or Bitbucket, then import it at vercel.com/new. Vercel detects Elysia automatically and deploys it with zero configuration.

From the CLI: From your project's root directory, run vercel to create a preview deployment, then vercel --prod to go live. To pull project settings and environment variables for local development, run:

vercel link
vercel env pull

For Vercel to detect your app, export your Elysia instance as the default export from one of the recognized entry files, such as app.ts, index.ts, or server.ts at your project root or under src/:

// For Node.js, ensure "type": "module" in package.json
// (Not required for Bun)
import { Elysia } from 'elysia';

const app = new Elysia().get('/', () => ({
  message: 'Hello from Elysia on Vercel!',
}));

export default app;

Running your application with app.listen() is currently not supported on Vercel. Use the default export instead, and if you're running on Node.js, set "type": "module" in your package.json:

{
  "name": "elysia-app",
  "type": "module"
}

After your app is deployed, you can layer Vercel features onto it. Some work automatically, and others take a few lines of configuration in vercel.json.

Each route in your Elysia app is served by Vercel Functions. These functions use Fluid compute by default, which runs multiple requests concurrently within a single instance to reduce cold starts and the cost of I/O-bound work such as API calls and database queries. You don't configure anything to get this behavior.

Because Elysia exports a single app, Vercel sends every incoming request to that app and lets Elysia's router match the path. Your route handlers, lifecycle hooks, and error handling all run inside Vercel Functions.

Vercel Functions support streaming, so you can send data to the client as you produce it instead of waiting for the full response. Elysia streams responses out of the box when you write your handler as a generator function with the yield keyword, and the sse utility formats yielded values as server-sent events:

import { Elysia, sse } from 'elysia';

const app = new Elysia()
  .get('/stream', function* () {
    for (const chunk of ['Hello', ' ', 'from', ' ', 'Elysia']) {
      yield chunk;
    }
  })
  .get('/events', function* () {
    yield sse({ event: 'message', data: { status: 'started' } });
    yield sse({ event: 'message', data: { status: 'done' } });
  });

export default app;

If a client disconnects before the response completes, Elysia automatically stops the generator. Streaming pairs well with Fluid compute: while your function waits between chunks, the same instance can serve other requests. Elysia also accepts a ReadableStream as a return value, which makes it straightforward to stream model output from AI SDK.

Elysia and Vercel each have a layer for running code around requests, and they solve different problems. Elysia's plugins and lifecycle hooks run inside your app's router, after the request reaches your function. Use them for app-level concerns such as logging, authentication, and request processing:

import { Elysia } from 'elysia';

const app = new Elysia()
  .onBeforeHandle(({ request }) => {
    // Runs before the route handler
    console.log('Request:', request.url);
  })
  .onAfterHandle(({ response }) => {
    // Runs after the route handler
    console.log('Response sent');
  })
  .get('/', () => 'Hello Elysia!');

export default app;

Vercel Routing Middleware runs at the edge, before the request reaches your Elysia app. Use it for rewrites, redirects, and header changes that should happen before any function runs. The two layers work together, with Routing Middleware shaping the request at the edge and Elysia's lifecycle hooks handling it inside your app.

Vercel Cron Jobs trigger a route on a schedule by sending an HTTP GET request to it. Define a route in your Elysia app for the task, then register the schedule in vercel.json.

Define the route:

import { Elysia } from 'elysia';

const app = new Elysia().get('/api/cron/cleanup', ({ request, status }) => {
  if (
    request.headers.get('authorization') !== `Bearer ${process.env.CRON_SECRET}`
  ) {
    return status(401, 'Unauthorized');
  }

  // Run your scheduled work here

  return { ok: true };
});

export default app;

Register the schedule:

{
  "$schema": "https://openapi.vercel.sh/vercel.json",
  "crons": [{ "path": "/api/cron/cleanup", "schedule": "0 0 * * *" }]
}

Vercel runs cron jobs only on production deployments. To stop anyone else from calling the route, set a CRON_SECRET environment variable in your project settings. Vercel sends it as a Bearer token in the Authorization header on every cron invocation, and your handler compares it before running the task.

Elysia runs your functions on Node.js by default. Since Elysia is optimized for Bun, you may want to run them on Bun instead. Set bunVersion in vercel.json:

{
  "$schema": "https://openapi.vercel.sh/vercel.json",
  "bunVersion": "1.x"
}

Vercel detects the setting, runs your app on Bun in both vercel dev and production, and keeps it on Fluid compute. The Bun runtime is in public beta and supports most Node.js APIs. Set the major version only, and Vercel manages the minor and patch versions. On Bun, you also don't need "type": "module" in your package.json.

Vercel Observability tracks your deployed functions automatically, with no setup. Open the Observability page in your project to see invocation counts, error rates, and duration for your Elysia app, along with the requests your functions make to external APIs. On Observability Plus, you also get longer retention and a latency breakdown by path.

Vercel finds your Elysia app by looking for a default export at a fixed set of locations: app, index, or server (with a .js, .ts, or related extension) at your project root or under src/. Put your app at one of these paths so Vercel detects and deploys it correctly:

import { Elysia } from 'elysia';

const app = new Elysia();

// Add your routes here

export default app;

Remember that app.listen() is not supported on Vercel. Export the app instead, and let Vercel Functions handle the server lifecycle.

Run vercel dev for local development instead of a standalone server. It serves your app the same way production does, using your default export, so the behavior you test locally matches what you deploy. This also lets you exercise features such as cron routes and the Bun runtime before shipping.

• Read the full Elysia on Vercel documentation
• Deploy the Elysia on Vercel template in one step
• Learn how Vercel Functions run your server code
• Understand pricing and scaling with Fluid compute
• Run code before requests with Routing Middleware
• Run your functions on the Bun runtime, or defer background work with Vercel Queues