MongoDB HealthChecker

Purpose

With the advent of the Node MongoDB Official Driver v4 and the forced use of the unified topology the isConnected check available in the driver will always return true. However you might want to track down whether the connection is actually ready and usable.

How

By simply importing the library and provide it with a configured MongoDB Client you'll be provided with two functions isUp and isReady to check whether the connection is available and operate accordingly.

const { MongoClient } = require('mongodb')
const mongoDBHealthChecker = require('@mia-platform/mongodb-healthchecker')

const client = new MongoClient(...)

// Note: the health checker must be connected before the MongoDB client connects,
//       since the checker relies on MongoDB events. On the contrary, it might happen
//       that connection events are fired before the listener is registered and
//       thus resulting in an always falsy readiness check
const { isReady, isUp } = mongoDBHealthChecker(client)

await client.connect()

const isConnectionReady = await isReady()
const isConnectionUp = await isUp()

Framework integration

Fastify

When you whish to integrate the mongodb-healthchecker library with the fastify framework you can use @fastify/mongodb and fastify-plugin to help you out in setting up the healthchecker.

Keep in mind there's an open issue on fastify integration that may impact services using isReady due to fastify delay in plugin registration.

The suggested way to integrate the library with fastify right now is to just use the isUp function, see below:

const fastifyMongodb = require('fastify-mongodb')
const fp = require('fastify-plugin')
const mongoDBHealthChecker = require('@mia-platform/mongodb-healthchecker')

....

const fastify = new Fastify(...)

fastify
  .register(fastifyMongodb, {
    url: MONGODB_URL,
    useNewUrlParser: true,
    useUnifiedTopology: true,
  })
  .register(fp(async function setupMongoDBHealthChecker(fastify) {
    const { isUp } = mongoDBHealthChecker(fastify.mongo.client)
    fastify.decorate('mongoDBCheckIsUp', isUp)
  }))