Node.js hot-reloading using Cluster

app.js

const express = require('express')

const app = express()

app.get('/', (req, res) => {
    res.status(200)
       .contentType('application/json')
       .json({ hello: 'world' })
})

module.exports = app

package.json

{
  "name": "hotreload-example",
  "version": "1.0.0",
  "author": "Luis Farzati <lfarzati@gmail.com>",
  "scripts": {
    "start": "node .",
    "dev": "NODE_ENV=development npm start"
  },
  "dependencies": {
    "express": "^4.15.2"
  },
  "devDependencies": {
    "chokidar": "^1.6.1"
  }
}

runner.js

const start = () => {
    require('./app').listen(3000, () => console.log(`Server ready at port 3000`))
}

if (process.env.NODE_ENV !== 'development') {
    return start()
}

const fork = (cluster) => {
    let worker = cluster.fork()
    worker.on('disconnect', () => console.log(`[WORKER-${worker.id}] terminated`))
    console.log(`[MASTER] forked worker ${worker.id}`)
    return worker    
}

const setupMaster = (cluster) => {
    const chokidar = require('chokidar')
    const watcher = chokidar.watch('./app')

    let worker = fork(cluster)

    watcher.on('ready', () => {
        watcher.on('all', (event, filename) => {
            worker.send({ type: 'hotreload', args: { filename, id: worker.id } })
            setTimeout(((worker) => () => worker.kill())(worker), 1000)
            process.nextTick(() => worker = fork(cluster))
        })
    })
}

const cluster = require('cluster')

if (cluster.isMaster) {
    setupMaster(cluster)
}
else if (cluster.isWorker) {
    start()
    process.on('message', ({type, args}) => {
        if (type === 'hotreload') {
            console.log(`[WORKER-${args.id}] Hot-reloading ${args.filename}`)
            delete require.cache[require.resolve(`./${args.filename}`)]
            process.disconnect()
        }
    })
}