npm i nanny


Scaffolding for node cluster

by tom

1.0.1 (see all)TypeScript:Not Found
npm i nanny


In some sense, a nanny watches kids. This module provides a cluster supervisor. A cluster is a group of worker processes that share a server or servers. The cluster supervisor:

  • maintains a pool of workers,
  • monitors the health of the workers including event loop responsiveness and memory consumption,
  • restarts workers if they stop,
  • stops workers if they fail a health check,
  • distributes incoming connections to the cluster workers

The cluster supervisor manages workers and load balancers. This package provides a round robin load balancer. Each connection will go to the least recently connected worker.

Worker processes do not require any special programming to participate in a cluster. The worker will be loaded in proxy by a “thunk” worker that will establish communication with the cluster supervisor, subvert Node.js's networking stack, and execute the worker module. Any attempt to listen for incomming connections with a net, http, or https server will be intercepted and managed by the cluster.


// launcher.js
var ClusterSupervisor = require("nanny");
var supervisor = new ClusterSupervisor({

    workerPath: path.join(__dirname, "worker.js"),
    workerArgv: [],             // Arguments to pass to your worker.
    workerCount: 8,             // Number of workers to spawn. Default is # cores.
    logicalIds: [5, 6, 7]       // Give workers an env variable
                                // "PROCESS_LOGICAL_ID" based on the values in
                                // the array and the order of the array.

    // Configure the supervisor's behavior:

    pulse: 1000,                // The interval at which workers will attempt
                                // to submit their memory usage and load statistics.
    unhealthyTimeout: 10e3,     // The maximum delay in miliseconds after an
                                // expected heart beat that a worker supervisor
                                // will tolerate before stopping a stalled
                                // worker.
    serverRestartDelay: 1000,   // The period that a load balancer will wait before
                                // attempting to restart a socket server.
    workerForceStopDelay: 1000, // The period that a worker supervisor will wait between
                                // a stop command and when it will
                                // automatically force stop with a kill signal.
                                // Set to Infinity to disable.
    workerRestartDelay: 1000,   // The period that a worker will wait between
                                // when a worker stops and when it will attempt
                                // to restart it.
    respawnWorkerCount: 1,      // When workers exit, retry spawning up to x
                                // times. -1 for infinite.

    // Override the child process parameters for each worker:

    execPath: '/usr/bin/node',  // An alternate Node.js binary to use to spawn
                                // worker processes.
    execArgv: [],               // An alternate set of command line arguments
                                // for Node.js to spawn the worker process.
    cwd: '/',                   // The working directory for each worker
                                // process.
    encoding: 'utf-8',          // Encoding for standard IO of the worker.
    silent: false,              // Pipes the worker standard IO into the
                                // supervisor process instead of inheriting the
                                // supervisor's own standard IO.

    // Introduce additional cluster supervisor initialization.
    // `this` is the cluster supervisor.
    initMaster: function() {

    // Override the method used to create the worker environment.
    // `this` is a worker supervisor and `` is its logical id.
    createEnvironment: function (logicalId) {
        return {
            PROCESS_LOGICAL_ID: logicalId

    // Override the health check method of the worker supervisor.
    // If this returns false, the worker process fails and will be stopped.
    // The health check will occur on the same interval as the worker's health
    // report (pulse) but may be offset by as much under normal conditions.
    isHealthy: function (health) {
        return health.memoryUsage.rss < 700e6;

    // Override the logger for the cluster. By default, we create a debuglog
    // named 'nanny' visible with `NODE_DEBUG=nanny`.
    logger: {
        debug: console.log.bind(console),
        warn: console.warn.bind(console),
        error: console.error.bind(console),


supervsior.forEachWorker(function (workerSupervisor) { });
supervisor.forEachLoadBalancer(function (loadBalancer) { });
// worker.js
process.title = 'worker';
// initialize worker stuff here...

execPath, execArgv, encoding, cwd, and silent are passed through to Node.js's own child_process.

The cluster supervisor, worker supervisors, and load balancers, are all event emitters.

The worker supervisor emits 'health' events when the child process reports its memory usage and load metrics.


var supervisor = new ClusterSupervisor(/*arguments*/)

ClusterSupervisor := (spec: SupervisorSpec) => void

This module abstracts logic for spawning workers via node cluster.


npm install nanny


npm test


  • tomuber
  • jakev
  • kriskowal

MIT Licensed