Fork Process in Cluster

index.js

const server = require('./server.js')
const numCPUs = require('os').cpus().length
const cluster = require('cluster')

function makeCluster() {
  return new Promise((resolve, reject) => {
    if (cluster.isMaster) {
      for (let i = 0; i < numCPUs; i++) {
        cluster.fork()
      }

      cluster.on('exit', (worker, code, signal) => {
        console.log(`Worker ${worker.process.pid} died`)
      })

      resolve()
    } else {
      console.log(`Fork ${cluster.worker.id} is spawning`)
      server.spawn()
        .then(resolve)
        .catch(reject)
    }
  })
}

makeCluster()
  .then(_ => {
    console.log('Child spawned')
  })
  .catch(e => {
    console.log(`Fork failed: ${e}`)
  })

server.js

module.exports = {
  spawn: function() {
    return new Promise(res => {
      console.log('[!!!!] Spawned process')
      res()
    })
  }
}