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Manuel Spigolon
Manuel Spigolon

Posted on • Updated on

Fastify demo goes to Production

To Production

This tutorial is the 3rd of a series. Read the previous ones
to get the codebase.

A Database

Things are getting serious, so it is time to connect the application to MongoDB because all applications
need a datasource and on the web there are old tutorials!

The first step is to get a database:

  • in the local environment a docker instance of mongodb will be used
  • in the CI we will use another docker instance
  • in production/Heroku we will connect to an Atlas MongoDB. It has a free plan that perfectly fits our needs!

DISCLAIMER: We will write tests too of course, but we will not write a single line of mocked code:

  • containers are cheap
  • you can't test a query with mocks
  • I think that DB state is not a con (this sentence could be a dedicated talk 😀)

Local database

This step is quite straighforward after installing Docker on your PC.

I like to add commands in the package.json:

  "local:mongo": "docker run -d -p 27017:27017 --rm --name mongoLocal mongo:4.2",
  "local:mongo:stop": "docker container stop mongoLocal"
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CI database

Thanks to GitHub Actions this step can be done with this configuration in the ci.yml file:

  - name: Start MongoDB
    uses: supercharge/mongodb-github-action@1.3.0
      mongodb-version: 4.2
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Production database

Atlas MongoDB gives us a free mongodb cluster on AWS! Awesome!

Project structure

Before digging into the code it is mandatory to focus a bit on the project structure to build and
maintain efficiently the application because now, things are getting serious.

Application vs Loader

Fastify is great in encapsulation and I found that following some rules allows developers to quickly build
applications with less discomforts.

The following example is a TL;DR version of the Testing
and Plugins-Guide pages.

The rules are:

  • An application.js file that expose module.exports = function buildApp (opts) {...
    This is THE APPLICATION factory, it loads all the plugins and the routes it needs and doesn't load the configuration.
    The configuration is read by opts parameter.

  • An start.js file that has 2 responsibilities:

  1. loading the configuration
  2. loading the application

This could be brief into this code example:

const config = await configurationLoader(process.argv[2] || process.env.NODE_ENV)
const app = require('./application.js')(config)
await app.listen(config.fastify.port,
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This structure will permit to load the application in a serverless environment, in a local PC
or in the CI servers without effort.


Loading the application configuration in a centralized point, and then propagate it throug all the application
components is very easy thanks to the .register parameters!

module.exports = function buildApp (opts) {
  const server = Fastify(opts.fastify)
  server.register(require('./routes'), opts) // the 2nd parameter of `register` is the configuration of the plugin!
  return server
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This is fundamental to avoid issues during tests implementation.

The key part is to write a loader (like the main start.js) for the application:

test('a test', async () => {
  const fakeConfig = await configurationLoader('test')
  const app = require('./application.js')(fakeConfig)
  const response = await app.inject({ ... })
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Fastify helps you apply separation of concerns design principle thanks to its encapsulation system.

This lead to applications more secure and better structured.

Is your database connection available where it is not necessary?

Thanks to encapsulation this could be avoided at all!


If the database is needed only in the right branch of the image, you can establish the database connection
only in the purple context:

  • the purple context and all its children can access the database connection
  • the left branch and the root itself will NOT be able access the DB

Keeping in mind the application tree structure, it is possible to design a highly modular software:

  • every branch of the tree can be moved to another fastify instance: this can be useful when a piece of your application became too big and deserve to be indipendent from the rest of your application
  • you can see patterns on your applications and build useful plugins to avoid repetitive work

Store the auth token

The token obatined from the OAUTH2 Code Flow should not be sent to the client to avoid security issues.

As example we will store the discord token in-memory on the server: this is not a scalable solution, but
it will works as a first step that will be evolved in the next blog post!

To archive this, the fastify-server-session plugin will
be used: it maps a generated SessionId, stored on the cookie's browser, to a server memory object.
Doing so we can implement the logic:

if (the request has not a session) {
  - proceed to authenticate the client with the Discord Authentication Server
  - create a session and store the token
  - view the user profile
} else {
  - view the user profile with the token associated with the request session
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Let's see the code..

The check we need to verify that the user is already logged in should be an onRequest hook:

fastify.addHook('onRequest', function userAlreadyLogged (req, reply, done) {
  if (req.session.token) {
    viewUserProfile(req.session.token, reply)
      .catch(done) // don't forget to manage errors!
    return // do not call `done` to stop the flow
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Hooks are one of the coolest features in Fastify!

The user log handler will be updated to:

fastify.get('/discord/callback', async function (request, reply) {
  const token = await this.discordOAuth2.getAccessTokenFromAuthorizationCodeFlow(request)
  // server stored: the token object must not be sent to the client
  request.session.token = token
  return viewUserProfile(token, reply)
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And it's done!

Connect to mongodb with Fastify

Fastify has a plugin for everything! This time it is the turn of fastify-mongodb!

To load it, it is necessary that the configuration is valid.
To do so we are using fastify-env already, but the Fastify plugin loading is totally async.
So, we must use after() accomplish this task:

import env from 'fastify-env'
// ...
fastify.register(env, { ... })
  .after((err) => {
    if (err) throw err // if the config file has some issue, we must bubble up it
    fastify.register(fastifyMongo, { url: fastify.config.DB_URI })
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WARNING: right now we will not focus on finding the best place to load the mongodb connection
as said in the Encapsulation paragraph. We will do this process in future in order to focus on security
steps and to learn how to refactor a Fastify application: we are starting small and learn fast!

Now the fastify.mongo decorator has been added to the instance and it will be accessible to
the instance itself and the children contexts.

At this stage, all the routes can access fastify.mongo!

So the new awesome feature will be to add a page that lists all the people that tried our application!
But this time the page will not be rendered through the server, but it will be loaded via REST API consumption.

Since in EU there is the GDPR regulamentation, we will not store the real people username, but a
fake-one in order to skip annoying messages and policies, because those are not tasks of this tutorial!

To isolate the APIs from the other application's components we create a brand new directory where all
the APIs will be implemented.

It is necessary to expose the fastify plugin interface as usual:

export default function api (fastify, opts, next) {
  // API context
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Then we can:

  • add a PUT endpoint to create/update the visitor
  • add a GET endpoint to read the visitor's book with pagination
  • define the input and the output JSON schemas to secure:
    • the input from malicous users input
    • the output from unnecessary data
// it keep the code strict as possible all the JSON schemas are in a dedicated file
import schema from './schema.mjs'

export default function api (fastify, opts, next) {

  // this context must return always JSON errors
  fastify.setErrorHandler(function (error, request, reply) {

  // the endpoint creates users
  fastify.put('/users/:userId', {
    handler: createUser,
    schema: schema.createUser

  // the endpoint searches for users
  fastify.get('/users', {
    handler: searchUsers,
    schema: schema.searchUsers


// write `function` to user the fastify instance as `this`
// the great thing is that you may organize these functions wherever you want in the project
// without struggling with tons of `factory-pattern` or clojures!
async function createUser (request, reply) {
  const { userId } = request.params

  await this.mongo.client.db()
      { id: userId },
        $set: request.body,
        $push: { visits: new Date() },
        $setOnInsert: { created: new Date() }
      { upsert: true })

  request.log.debug('Track user %s', userId) // fastify has a logger included!
  return { userId }

async function searchUsers (request, reply) {
  const { offset, limit } = request.query

  // just a simple pagination
  const query = await this.mongo.client.db().collection('Users')
    .find({}, { projection: { _id: 0, visits: { $slice: -1 } } })
    .sort({ 'visits.$0': 1 })

  const total = await query.count() // it doesn't apply the skip&limit 😉
  const rows = await query.toArray()

  return { rows, total }
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In the next post we will:

  • explore the project structure: is it maintainable?
  • protect the /api endpoints
  • migrate from stateful session to a stateless JWT
  • manage the Discord refresh token

For more Fastify content follow me on twitter!


Thank you very much to @LorTos for the great feedback!
Image post credits to jayahimsa (CC BY-NC 2.0)

Top comments (2)

mcastellin profile image
Manuel Castellin

Nice article, man! I didn't know you could start using a database on Atlas for free! That's huge if you want to try something out and don't want to pay for AWS storage 🤑
Do you know if you can create as many databases as you want with the free account?

eomm profile image
Manuel Spigolon

Yes! You can create as many db you need. You may create multiple "projects" with a separated free-cluster too and I didn't get any limitation warning