This article is also available on my blog: https://hamidreza.tech/nestjs-on-vercel.

This guide is beneficial if you're using Express adapter. For NestJS applications utilizing the Fastify adapter, these links may be helpful:

• https://fastify.dev/docs/latest/Guides/Serverless/#vercel

• https://github.com/vercel/examples/tree/main/starter/fastify

🚀 You can access the complete source code discussed in this article at this GitHub repository: https://github.com/mahdavipanah/nestjs-on-vercel

Vercel's Support for Express Apps

Vercel offers a convenient feature for deploying your Express app by:

1. Exposing the Express app object in an API.

2. Defining a rewrite rule that directs all incoming traffic to this single API.

I followed Vercel’s official guide for deploying Express to deploy NestJS by similarly exposing NestJS’s underlying Express app object.

Step 1 - create a NestJS app

Skip this step if you already have a NestJS app set up.

Install NestJS and create a new app:

nest new my-app

Step 2 - Install Necessary NPM Packages

npm install express @nestjs/platform-express
npm install -D @types/express

Step 3 - Create src/AppFactory.ts file

This file serves as a single module that manages all necessary NestJS app bootstrapping and exports both the NestJS app and its underlying Express app object.

Create a file named AppFactory.ts inside the src directory in your project’s root:

import { ExpressAdapter } from '@nestjs/platform-express';
import { NestFactory } from '@nestjs/core';
import express, { Request, Response } from 'express';
import { Express } from 'express';
import { INestApplication } from '@nestjs/common';
import { AppModule } from './app.module.js';

export class AppFactory {
  static create(): {
    appPromise: Promise<INestApplication<any>>;
    expressApp: Express;
  } {
    const expressApp = express();
    const adapter = new ExpressAdapter(expressApp);
    const appPromise = NestFactory.create(AppModule, adapter);

    appPromise
      .then((app) => {
        // You can add all required app configurations here

        /**
         * Enable cross-origin resource sharing (CORS) to allow resources to be requested from another domain.
         * @see {@link https://docs.nestjs.com/security/cors}
         */
        app.enableCors({
          exposedHeaders: '*',
        });

        app.init();
      })
      .catch((err) => {
        throw err;
      });

    // IMPORTANT This express application-level middleware makes sure the NestJS app is fully initialized
    expressApp.use((req: Request, res: Response, next) => {
      appPromise
        .then(async (app) => {
          await app.init();
          next();
        })
        .catch((err) => next(err));
    });

    return { appPromise, expressApp };
  }
}

Step 4 - Modify src/main.ts File

By default, NestJS has a src/main.ts file that serves as the entry point of the application, including all configuration and bootstrapping. Modify this file to move everything to the AppFactory.ts file, keeping only the invocation of the listen method:

import { AppFactory } from './AppFactory.js';

async function bootstrap() {
  const { appPromise } = AppFactory.create();
  const app = await appPromise;

  await app.listen(process.env.PORT ?? 3000);
}
bootstrap();

Step 5 - Add api/index.ts File

By default, the Vercel runtime builds and serves any function created within the /api directory of a project to Vercel (doc). Since Vercel understands and handles the Express app object, create a function inside this directory that exports the Express app object:

/**
 * This file exports Express instance for specifically for the deployment of the app on Vercel.
 */

import { AppFactory } from '../src/AppFactory.js';

export default AppFactory.create().expressApp;

Step 6 - Add vercel.json File

Create a file named vercel.json in the project’s root directory to configure Vercel. Here, define a rewrite rule for Vercel to use the Express app to serve all incoming traffic (doc).

You can also use a tsconfig.json file at the api directory to configure the Vercel’s TypeScript compiler. Most options are supported aside from "Path Mappings" and "Project References".

{
  "version": 2,
  "buildCommand": "npm run build",
  "outputDirectory": ".",
  "rewrites": [
    {
      "source": "/(.*)",
      "destination": "/api"
    }
  ]
}

Step 7 - Create a Project on Vercel

Congratulations 🎉! We are almost done. Now, create a git repository and push your source code to it. Then, go to your Vercel account, create a new project, and import the git repository. You can also use this article’s example GitHub repository.