Express Example of master and workers killer

node_master_worker_express_example.js

'use strict'

const cluster = require('cluster')
const os = require('os')

if (cluster.isMaster) {
  let numOfWorkers = os.cpus().length

  console.log(`Master cluster setting up ${numOfWorkers} workers..`)
  for (let i=0; i < numOfWorkers; i++) {
    cluster.fork()
  }

  // Master receiving message from worker
  cluster.on('message', function(msg) {
    
    console.log('message received: ' + JSON.stringify(msg))

    if (cluster.workers[msg.workerId]) {
      cluster.workers[msg.workerId].send({
        command: 'kill',
        workerId: msg.workerId
      })
    } else {
      console.log('Worker already died...')
    }
  
  })

  cluster.on('online', (worker) => {
    console.log(`Worker ${worker.id} is online`)
  })

  cluster.on('exit', (worker, code, signal) => {
    console.log(`Worker ${worker.id} died with code ${code}`)
    console.log(`Starting a new worker`)
    cluster.fork()
  })
}

if (cluster.isWorker){
  let app = require('express')()

  // worker receiving message from master
  process.on('message', (msg) => {
    console.log(`worker ${cluster.worker.id} got message: ${JSON.stringify(msg)}`)
    if (msg.command == 'kill' && msg.workerId == cluster.worker.id) {
      console.log('-- killing this worker --')
      process.exit(0)
    }
  })

  app.all('/hello', (req, res) => {
    res.send(`Hello from process id ${process.id}`)
  })

  app.all('/kill/:wid', (req, res) => {
    try {
      const wid = req.params.wid
      // worker sending a message to master
      process.send({command: 'shutdown', workerId: wid})
      res.send('ok')

    } catch(e) {console.log(e)}
  })

  let server = app.listen(1818, () => {
    console.log(`Process ${process.pid} by worker id ${cluster.worker.id} is listening to all incoming requests`)
  })
}