Platformatic NestJS

The Platformatic NestJS allows to run a NestJS application as a Platformatic Runtime application with no modifications.

Getting Started

Create or copy a NestJS application inside the applications, services or web folder. If you are not using autoload, you also have to explictly add the new application.

You are all set, you can now start your runtime as usual via wattpm dev or wattpm start.

Install

npm install @platformatic/nest

Example configuration file

Create a watt.json in the root folder of your application with the following contents:

{
  "$schema": "https://schemas.platformatic.dev/@platformatic/nest/2.66.0.json",
  "application": {
    "basePath": "/frontend"
  }
}

Architecture

When starting NestJS in development mode, production mode or by using the commands property, Platformatic will choose a random port for the HTTP server and it will override any user or application setting.

Configuration

See the configuration page.

API

During application execution some APIs are made available in the globalThis.platformatic object.

• globalThis.platformatic.setBasePath(path): This function can be used to override the base path for the application. If not properly configured in the gateway, this can make your application inaccessible.
• globalThis.platformatic.applicationId: The id of the application.
• globalThis.platformatic.workerId: The id of the application worker.
• globalThis.platformatic.root: The root directory of the application.
• globalThis.platformatic.basePath: The base path of the application in the gateway.
• globalThis.platformatic.logLevel: The log level configured for the application.
• globalThis.platformatic.events.on('close'): This event is emitted when the process is being closed. A listener should be installed to perform a graceful close, which must finish in 10 seconds. If there is no listener, the process will be terminated by invoking process.exit(0).
• globalThis.platformatic.setCustomHealthCheck(fn): This function can be used to set a custom healthcheck function for the application. The function should return a boolean value, or an object with the following properties:
  • status: a boolean indicating if the health check is successful
  • statusCode: an optional HTTP status code
  • body: an optional body to return
• globalThis.platformatic.sendHealthSignal(signal): This function can be used to send a health signal from the application to the runtime.
  • signal: an object with the following properties:
    • type: a string with the type of the signal
    • value: an optional value to send with the signal.
    • description: an optional description of the signal.

The healthcheck function will ensure the readiness of the application, and the readiness check function will ensure the readiness of the application dependencies; if the healthcheck fails, the readiness check will fail, and the application will be marked as unhealthy; in this case, the liveness probe will return the readiness check response in the body.

• globalThis.platformatic.setCustomReadinessCheck(fn): This function can be used to set a custom readiness check function for the application. The function should return a boolean value, or an object with the following properties:

  • status: a boolean indicating if the readiness check is successful
  • statusCode: an optional HTTP status code
  • body: an optional body to return

• globalThis.platformatic.sharedContext.update(contextUpdate, options): This function can be used to update the shared context. Context is shared between all runtime applications.

  • contextUpdate: an object with the context updates
  • options: an optional object with the following properties:
    • overwrite: a boolean value indicating if the context should be overwritten or merged. Default is false

• globalThis.platformatic.sharedContext.get(): This function can be used to get the shared context.

Messaging API

Services can talk to each other using a messaging API available in the globalThis.platformatic.messaging object.

The messaging API contains the following functions:

• globalThis.platformatic.messaging.handle(message, handler): Registers a message handler for the specified message.

  • message: a string with the name of the message
  • handler: a function that will be invoked when a message with the specified name is received

• globalThis.platformatic.messaging.send(application, message, data, options): Sends a message to an application worker.

  • application: a string with the name of the application
  • message: a string with the name of the message
  • data: any cloneable JavaScript value. All non-cloneable values (functions, symbols, etc.) will be sanitized.
  • options: an optional object with the following properties:
    • transferList: a list of ArrayBuffer, MessagePort, and FileHandle objects. After transferring, they are not usable on the sending side of the channel anymore.

The send method sends a message to one receiving application worker using a round-robin algorithm. The send method awaits for the response from the message handler. By default it uses a 30s timeout. To change the timeout, update the messagingTimeout option in the watt configuration.

• globalThis.platformatic.messaging.notify(application, message, data): Notifies all application workers with a message.
  • application: a string with the name of the application
  • message: a string with the name of the message
  • data: any cloneable JavaScript value. All non-cloneable values (functions, symbols, etc.) will be sanitized.

The notify method sends a message to all application workers. It does not wait for the response from the message handler. Notification messages are exchanged using Node.js BroadcastChannel. The data must be cloneable value. All non-cloneable values (functions, symbols, etc.) will be sanitized.

Once an application adds a handler via globalThis.platformatic.messaging.handle API, then any other application can invoke the function using the globalThis.platformatic.messaging.send API. If an application makes a send call, before a handler is registered, the send call throws an error. To make sure that an application is ready, use a runtime dependencies API.

Here is an example:

// web/service/index.js

globalThis.platformatic.messaging.handle({
  async time ({ offset }) {
    return Date.now() + offset
  }
})

The send method sends a message to one receiving application worker using a round-robin algorithm.

// web/entrypoint/index.js

app.get('/time', async req => {
  const response = await globalThis.platformatic.messaging.send('application', 'time', { offset: 1000 })

  return { thread: response }
})

The notify method sends a message to all application workers. Notification messages are exchanged using Node.js BroadcastChannel

// web/entrypoint/index.js

app.get('/time', async req => {
  globalThis.platformatic.messaging.notify('application', 'time', { offset: 1000 })

  return { thread: 'ok' }
})

Note that messages are exchanged using Node.js MessageChannel so you must eventually provide a transferList as via the send options:

const { port1, port2 } = new MessageChannel()
const response = await globalThis.platformatic.messaging.send(
  'application',
  'connect',
  { port: port1 },
  { transferList: [port1] }
)

Custom Metrics

Custom metrics can be registered and exported by accessing the same Prometheus registry that the rest of the Platformatic runtime is using via globalThis.platformatic.prometheus.registry.

In order to ensure the maximum compatibility the client package (prom-client) is available in globalThis.platformatic.prometheus.client.

Here is an example of how to register a custom metric:

const { client, registry } = globalThis.platformatic.prometheus

// Register the metric
const customMetrics = new client.Counter({ name: 'custom', help: 'Custom Description', registers: [registry] })

// ...

// Later increase the value
customMetrics.inc(123)

note

Remember that it is a good practice to register metrics as soon as possible during the boot phase.

Typings for the API

In order to get full Typescript support for the API above, you can install the @platformatic/globals package and get an alternative, typed, access to the globalThis.platformatic object.

The usage of the package is straightforward:

import { getGlobal } from '@platformatic/globals'

const pltApi = getGlobal()

Custom Healthcheck

Custom health check can be defined to provide more specific and detailed information about the health of your application, in case the default healthcheck for the application itself is not enough and you need to add more checks for the application dependencies.

This can be done by using the setCustomHealthCheck method available on the globalThis.platformatic object, and run it as a Platformatic application.

The function should return a boolean value, or an object with the following properties, that will be used to set the status code and body of the response to the healthcheck endpoint:

• status: required a boolean value
• statusCode: optional an HTTP status code
• body: optional an HTTP response body

Here is an example of how to set a custom health check:

app.js

import fastify from 'fastify'

export function create () {
  const app = fastify()

  globalThis.platformatic.setCustomHealthCheck(async () => {
    return Promise.all([
      // Check if the database is reachable
      app.db.query('SELECT 1'),
      // Check if the external application is reachable
      fetch('https://payment-application.com/status')
    ])
  })

  app.get('/', (req, res) => {
    res.send('Hello')
  })

  return app
}

Setting custom response for the healthcheck endpoint:

import fastify from 'fastify'

export function create () {
  const app = fastify()

  globalThis.platformatic.setCustomHealthCheck(async () => {
    // Check if the database is reachable
    if (!app.db.query('SELECT 1')) {
      return {
        status: false,
        statusCode: 500,
        body: 'Database is unreachable'
      }
    }
    // Check if the external service is reachable
    const payment = await fetch('https://payment-service.com/status')
    if (!payment.ok) {
      return {
        status: false,
        statusCode: 500,
        body: 'Payment service is unreachable'
      }
    }
  })

  globalThis.platformatic.setCustomReadinessCheck(async () => {
    return Promise.all([
      // Check if the database is reachable
      app.db.query('SELECT 1'),
      // Check if the external service is reachable
      fetch('https://payment-service.com/status')
    ])
  })

  app.get('/', (req, res) => {
    res.send('Hello')
  })

  return app
}

platformatic.json

{
  "$schema": "https://schemas.platformatic.dev/@platformatic/node/2.51.0.json"
}

package.json

{
  "type": "module",
  "name": "application-node",
  "version": "1.0.0",
  "main": "app.js",
  "scripts": {
    "start": "wattpm start"
  },
  "dependencies": {
    "fastify": "^5.0.0",
    "@platformatic/node": "^2.48.0"
  }
}

Issues

If you run into a bug or have a suggestion for improvement, please raise an issue on GitHub or join our Discord feedback channel.