Migrating an Express app to Platformatic Service

Introduction

Our open-source tools are built on top of the modern and flexible Fastify web framework. It provides logging, request validation and a powerful plugin system out-of-the-box, as well as incredible performance.

If you have an existing Express application, migrating it to Fastify could potentially be time consuming, and might not be something that you're able to prioritise right now. You can however still take advantage of Fastify and our open-source tools. In this guide you'll learn how to use the @fastify/express plugin to help you rapidly migrate your existing Express application to use Platformatic Service.

This guide assumes that you have some experience building applications with the Express framework.

Example Express application

For the purpose of this guide, we have a basic example Express application. Although this app has a specific structure, the migration steps covered in this guide can generally be applied to any Express application.

The code for the example Express and migrated Platformatic Service applications is available on GitHub.

Here's the structure of the example Express application:

├── app.js
├── package.json
├── routes
│   └── users.js
└── server.js

It has the following dependencies:

// package.json

"dependencies": {
  "express": "^4.18.2"
}

The application has routes in routes/users.js:

// routes/users.js

import express from 'express'

const router = express.Router()

router.use(express.json())

router.post('/', function createUser(request, response, next) {
  const newUser = request.body

  if (!newUser) {
    return next(new Error('Error creating user'))
  }

  response.status(201).json(newUser)
})

router.get('/:user_id', function getUser(request, response, next) {
  const user = {
    id: Number(request.params.user_id),
    first_name: 'Bobo',
    last_name: 'Oso'
  }

  response.json(user)
})

export const usersRoutes = router

In app.js, we have a factory function that creates a new Express server instance and mounts the routes:

// app.js

import express from 'express'

import { usersRoutes } from './routes/users.js'

export default function buildApp() {
  const app = express()

  app.use('/users', usersRoutes)

  return app
}

And in server.js we're calling the factory function and starting the server listening for HTTP requests:

// server.js

import buildApp from './app.js'

const express = buildApp()

express.listen(3042, () => {
  console.log('Example app listening at http://localhost:3042')
})

The routes in your Express application should be mounted on an Express router (or multiple routers if needed). This will allow them to be mounted using @fastify/express when you migrate your app to Platformatic Service.

Creating a new Platformatic Service app

To migrate your Express app to Platformatic Service, create a new Platformatic Service app with:

npm create platformatic@latest

Be sure to select Service as the project type.

Once the project has been created, you can delete the example plugins and routes directories.

Using ES modules

If you're using ES modules in the Express application code that you'll be migrating, ensure that there's a type field in package.json set to module:

npm pkg set type=module

Migrate the Express routes

Copy over the routes directory from your Express app.

Install @fastify/express

Install the @fastify/express Fastify plugin to add full Express compatibility to your Platformatic Service app:

npm install @fastify/express

Mounting the Express routes

Create a root Fastify plugin that register's the @fastify/express plugin and loads your Express routes:

// root-plugin.js

import { usersRoutes } from './routes/users.js'

/** @param {import('fastify').FastifyInstance} app */
export default async function (app) {
  await app.register(import('@fastify/express'))

  app.use('/users', usersRoutes)
}

Configuring the Platformatic Service app

Edit your app's platformatic.service.json to load your root plugin:

// platformatic.service.json

{
  ...,
  "plugins": {
    "paths": [{
      "path": "./root-plugin.js",
      "encapsulate": false
    }]
  }
}

These settings are important when using @fastify/express in a Platformatic Service app:

• encapsulate — You'll need to disable encapsulation for any Fastify plugin which mounts Express routes. This is due to the way that @fastify/express works.

Using @fastify/express with Platformatic Runtime

If you are using Platformatic Runtime, you must configure your other services to connect to this one using an actual TCP socket instead of the virtual network.

Edit your app's platformatic.runtime.json and add the useHttp option:

{
  "$schema": "https://platformatic.dev/schemas/v1.3.0/runtime",
  "entrypoint": "b",
  "autoload": {
    "path": "./services",
    "mappings": {
      "myexpressservice": {
        "id": "a",
        "config": "platformatic.service.json",
        "useHttp": true
      }
    }
  },
  "server": {
    "hostname": "127.0.0.1",
    "port": 3000,
    "logger": {
      "level": "info"
    }
  }
}

Where the Platformatic Service using express is located at ./services/myexpressservice.

Wrapping up

You can learn more about building Node.js apps with Platformatic service in the Platformatic Service documentation.

Once you've migrated your Express app to use Platformatic Service with @fastify/express, you might then want to consider fully migrating your Express routes and application code to Fastify. This tutorial shows how you can approach that migration process: How to migrate your app from Express to Fastify (video).