Linux Node JS HTTP Daemon

daemon.js

#!/usr/bin/env node

/**
 * bin/daemon
 * A simple Linux HTTP Daemon
 */

require('daemon')();

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

/**
 * Creates a new worker when running as cluster master.
 * Runs the HTTP server otherwise.
 */
const createWorker = () => {
  if(cluster.isMaster) {
    let child = cluster.fork();

    child.on('exit', (code, signal) => {
      createWorker();
    });
  } else {
    require('../app');
  }
};

/**
 * Creates the specified number of workers.
 * @param  {Number} n Number of workers to create.
 */
const createWorkers = (n) => {
  while (n-- > 0) {
    createWorker();
  }
};

/**
 * Kills all workers with the given signal.
 * Also removes all event listeners from workers before sending the signal
 * to prevent respawning.
 * @param  {Number} signal
 */
const killAllWorkers = (signal) => {
  Object.keys(cluster.workers).forEach((id) => {
    let worker = cluster.workers[id];

    worker.removeListener();
    worker.process.kill(signal);
  });
};

/**
 * Restarts the workers
 */
process.on('SIGHUP', () => {
  killAllWorkers('SIGTERM');
  createWorkers(numCPUs * 2);
});

/**
 * Gracefully shutdown the workers
 */
process.on('SIGTERM', () => {
  killAllWorkers();
});

createWorkers(numCPUs * 2);