Simple Cluster example for Node.js

cluster.js

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

if (cluster.isMaster) {
    console.log(`Master ${process.pid} is running`)

    // Basic Multi-process Functionality
    for (let i = 0; i < numCPUs; i++) {
        cluster.fork()
    }

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

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

    // Seamless Restarting
    const workers = Object.values(cluster.workers)

    const restartWorker = workerIndex => {
        const worker = workers[workerIndex]
        if (!worker) return
      
        worker.on('exit', () => {
          if (!worker.exitedAfterDisconnect) return
          console.log(`Exited process ${worker.process.pid}`)
          
          cluster.fork().on('listening', () => {
            restartWorker(workerIndex + 1)
          })
        })
      
        worker.disconnect()
    }

    process.on('SIGUSR2', () => {
        console.log('SIGUSR2 signal received, restarting workers')
        restartWorker(0)
    })
} else {
    // Code here
    console.log(`Worker ${process.pid} started`)
}