cluster.js

const cluster = require("cluster")

const http = require("http")
const cpuCount = require("os").cpus().length //returns no of cores our cpu have
if (cluster.isMaster) {
  masterProcess()
} else {
  childProcess()
}
function masterProcess() {
  console.log(`Master process ${process.pid} is running`)
  //fork workers.
  for (let i = 0; i < cpuCount; i++) {
    console.log(`Forking process number ${i}...`)
    cluster.fork() //creates new node js processes
  }
  cluster.on("exit", (worker, code, signal) => {
    console.log(`worker ${worker.process.pid} died`)
    cluster.fork() //forks a new process if any process dies
  })
}
function childProcess() {
  const express = require("express")
  const app = express()
  //workers can share TCP connection
  app.get("/", (req, res) => {
    res.send(`hello from server ${process.pid}`)
  })
  app.listen(5555, () =>
    console.log(`server ${process.pid} listening on port 5555`)
  )
}