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Turns your single process code into a fault-resilient multi-process service with built-in REST & CLI support

Version published
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931 kB



v2.1.4 - 9/21/2020


  • Dependency updates.




Build Status NPM version Dependency Status Bitdeli Badge



npm install cluster-service


Turn your single process code into a fault-resilient, multi-process service with
built-in REST & CLI support. Restart or hot upgrade your web servers with zero
downtime or impact to clients.



Getting Started

Your existing application, be it console app or service of some kind:

// server.js
console.log("Hello World");

Leveraging cluster-service without adding a line of code:

npm install -g cluster-service
cservice "server.js" --accessKey "lksjdf982734"
// cserviced "server.js" --accessKey "lksjdf982734" // daemon

This can be done without a global install as well, by updating your package.json:

"scripts": {
	"start": "cservice server.js --accessKey lksjdf982734"
"dependencies": {
	"cluster-service": ">=0.5.0"

Now we can leverage npm to find our local install of cluster-service:

npm start

Or, if you prefer to control cluster-service within your code, we've got you covered:

// server.js
require("cluster-service").start({ workers: "./worker.js", accessKey: "lksjdf982734" });

// worker.js
console.log("Hello World"); // notice we moved our original app logic to the worker

Talk to it

Now that your service is resilient to worker failure, and utilizing all cores of your machine, lets talk to it. With your service running, type into the command-line:

restart all

or for a full list of commands...


or for help on a specific command:

help {command}

We can also issue commands from a seperate process, or even a remote machine (assuming proper access):

npm install -g cluster-service
cservice "restart all" --accessKey "my_access_key"

You can even pipe raw JSON for processing:

cservice "restart all" --accessKey "my_access_key" --json

Check out Cluster Commands for more.

Start Options

When initializing your service, you have a number of options available:

cservice "server.js" --accessKey "123"

Or via JSON config:

cservice "config.json"

Or within your node app:

// server.js
// inline options
require("cluster-service").start({ workers: "worker.js", accessKey: "123" });
// or via config
require("cluster-service").start({ config: "config.json" });


  • workers - Path of worker to start. A string indicates a single worker, forked based on value of workerCount. An object indicates one or more worker objects: { "worker1": { worker: "worker1.js", cwd: process.cwd(), count: 2, restart: true } }. This option is automatically set if run via command-line cservice "worker.js" if the .js extension is detected.
  • accessKey - A secret key that must be specified if you wish to invoke commands from outside your process. Allows CLI & REST interfaces.
  • config - A filename to the configuration to load. Useful to keep options from having to be inline. This option is automatically set if run via command-line cservice "config.json" if the .json extension is detected.
  • host (default: "localhost") - Host to bind to for REST interface. (Will only bind if accessKey is provided)
  • port (default: 11987) - Port to bind to. If you leverage more than one cluster-service on a machine, you'll want to assign unique ports. (Will only bind if accessKey is provided)
  • workerCount (default: os.cpus().length) - Gives you control over the number of processes to run the same worker concurrently. Recommended to be 2 or more to improve availability. But some workers do not impact availability, such as task queues, and can be run as a single instance.
  • cli (default: true) - Enable the command line interface. Can be disabled for background services, or test cases. Running cserviced will automatically disable the CLI.
  • ssl - If provided, will bind using HTTPS by passing this object as the TLS options.
  • run - Ability to run a command, output result, and exit. This option is automatically set if run via command-line cservice "restart all" and no extension is detected.
  • json (default: false) - If specified in conjunction with run, will only output the result in JSON for consumption from other tasks/services. No other data will be output.
  • silent (default: false) - If true, forked workers will not send their output to parent's stdio.
  • allowHttpGet (default: false) - For development purposes, can be enabled for testing, but is not recommended otherwise.
  • restartOnMemUsage (default: disabled) - If a worker process exceeds the specified memory threshold (in bytes), the process will be restarted gracefully. Only one worker will be restarted at a time.
  • restartOnUpTime (default: disabled) - If a worker process exceeds the specified uptime threshold (in seconds), the process will be restarted gracefully. Only one worker will be restarted at a time.
  • restartConcurrencyRatio (default 0.33) - The ratio of workers that can be restarted concurrently during a restart or upgrade process. This can greatly improve the speed of restarts for applications with many concurrent workers and/or slow initializing workers.
  • commands - A single directory, an array of directories, or a comma-delimited list of directories may be provided to auto-register commands found in the provided folders that match the ".js" extension. If the module exposes the "id" property, that will be the name of the command, otherwise the filename (minus the extension) will be used as the name of the command. If relative paths are provided, they will be resolved from process.cwd().
  • master - An optional module to execute for the master process only, once start has been completed.
  • proxy - Optional path to a JSON config file to enable Proxy Support.
  • workerGid - Group ID to assign to child worker processes (recommended nobody).
  • workerUid - User ID to assign to child worker processes (recommended nobody).

Console & REST API

A DPS Cluster Service has two interfaces, the console (stdio), and an HTTP REST API. The two interfaces are treated identical, as console input/output is piped over the REST API. The reason for the piping is that a DPS Cluster Service is intentionally designed to only support one instance of the given service running at any one time, and the port binding is the resource constraint. This allows secondary services to act as console-only interfaces as they pipe all input/output over HTTP to the already running service that owns the port. This flow enables the CLI to background processes. The REST API is locked to a "accessKey" expected in the query string. The console automatically passes this key to the REST API, but for external REST API access, the key will need to be known.

{ host: "localhost", port: 11987, accessKey: "lksjdf982734" }

Invoking the REST interface directly would look something like:

curl -d "" "http://localhost:11987/cli?cmd=help&accessKey=lksjdf982734"

Or better yet, use the run option to do the work for you:

cservice "help" --accessKey "lksjdf982734"
// same as
cservice --run "help" --accessKey "lksjdf982734"

Cluster Commands

While a Cluster Service may provide its own custom commands, below are provided out-of-the-box. Commands may be disabled by overriding them.

  • start workerPath [cwd] { [timeout:60000] } - Gracefully start service, one worker at a time.
  • restart all|pid { [timeout:60000] } - Gracefully restart service, waiting up to timeout before terminating workers.
  • shutdown all|pid { [timeout:60000] } - Gracefully shutdown service, waiting up to timeout before terminating workers.
  • exit now - Forcefully exits the service.
  • help [cmd] - Get help.
  • upgrade all|pid workerPath { [cwd] [timeout:60000] } - Gracefully upgrade service, one worker at a time. (continuous deployment support).
  • workers - Returns list of active worker processes.
  • health - Returns health of service. Can be overidden by service to expose app-specific data.
  • info - Returns summary of process & workers.

Commands & Events

Creating custom, or overriding commands and events is as simple as:

cservice "server.js" --commands "./commands,../some_more_commands"

Or if you prefer to manually do so via code:

var cservice = require("cluster-service");
cservice.on("custom", function(evt, cb, arg1, arg2) { // "custom" command
	// can also fire custom events
	cservice.trigger("on.custom.complete", 1, 2, 3);

cservice.on("test", function(evt, cb, testScript, timeout) { // we're overriding the "test" command
	// arguments
	// do something, no callback required (events may optionally be triggered)

// can also issue commands programatically
cservice.trigger("custom", function(err) { /* my callback */ }, "arg1value", "arg2value");

Cluster Events

Events are emitted to interested parties.

  • workerStart (pid, reason) - Upon exit of any worker process, the process id of the exited worker. Reasons include: "start", "restart", "failure", and "upgrade".
  • workerExit (pid, reason) - Upon start of any worker process. Reasons include: "start", "restart", "failure", and "upgrade".

Async Support

While web servers are automatically wired up and do not require async logic (as of v1.0), if your service requires any other asynchronous initialization code before being ready, this is how it can be done.

Have the worker inform the master once it is actually ready:

// worker.js
require("cluster-service").workerReady(false); // we're NOT ready!
setTimeout(funtion() {
	// dumb example of async support
	require("cluster-service").workerReady(); // we're ready!
}, 1000);

Additionally, a worker may optionally perform cleanup tasks prior to exit, via:

// worker.js
	onWorkerStop: function() {
		// lets clean this place up
		process.exit(); // we're responsible for exiting if we register this cb

Access Control

Commands may be granted "inproc" (high risk), "local" (low risk), or "remote" (no risk). Setting access control can be done within the command, like so:

// exit.js
module.exports.control = function(){
	return "local";

Or may be overriden at runtime via:

// server.js
require("cluster-service").control({ "exit": "local" });

Proxy Support

Proxy mode specifically caters to Web Servers that you want to enable automatic versioning of your service. Any version requested (via versionHeader) that is not yet loaded will automatically have a worker process spun up with the new version, and after ready, the proxy will route to that worker.

Every version of your app must adhere to the PROXY_PORT environment variable like so:

require("http").createServer(function(req, res) {
  res.end("Hello world!");
}).listen(process.env.PROXY_PORT || 3000 /* port to use when not running in proxy mode */);

Proxy Options

  • versionPath (default: same directory as proxy JSON config) - Can override to point to a new version folder.
  • defaultVersion - The version (folder name) that is currently active/live. If you do not initially set this option, making a request to the Proxy without a versionHeader will result in a 404 (Not Found) since there is no active/live version. Upgrades will automatically update this option to the latest upgraded version.
  • versionHeader (default: x-version) - HTTP Header to use when determining non-default version to route to.
  • workerFilename (default: worker.js) - Filename of worker file.
  • bindings (default: [{ port: 80, workerCount: 2 }]) - An array of Proxy Bindings.
  • versionPorts (default: 11000-12000) - Reserved port range that can be used to assign ports to different App versions via PROXY_PORT.
  • nonDefaultWorkerCount (default: 1) - If a version is requested that is not a default version, this will be the number of worker processes dedicated to that version.
  • nonDefaultWorkerIdleTime (default: 3600) - The number of seconds of inactivity before a non-default version will have its workers shut down.

Proxy Bindings

Binding options:

  • port - Proxy port to bind to.
  • workerCount (default: 2) - Number of worker processes to use for this binding. Typically more than 2 is unnecessary for a proxy, and less than 2 is a potential failure point if a proxy worker ever goes down.
  • tlsOptions - TLS Options if binding for HTTPS.
    • key - Filename that contains the Certificate Key.
      • cert - Filename that contains the Certificate.
      • pem - Filename that contains the Certificate PEM if applicable.

A full list of TLS Options:

Proxy Commands

Work like any other Cluster Commands.

  • proxy start configPath - Start the proxy using the provided JSON config file.
  • proxy stop - Shutdown the proxy service.
  • proxy version workerVersion workerCount - Set a given App version to the desired number of worker processes. If the version is not already running, it will be started. If 2 workers for the version are already running, and you request 4, 2 more will be started. If 4 workers for the version are already running, and you request 2, 2 will be stopped.
  • proxy promote workerVersion workerCount - Works identical to the proxy version command, except this will flag the version as active/live, resulting in the Proxy Config file being updated with the new defaultVersion.
  • proxy info - Fetch information about the proxy service.

Tests & Code Coverage

Download and install:

git clone
cd node-cluster-service
npm install

Now test:

npm test

View code coverage in any browser:


Change Log

Change Log





Last updated on 21 Sep 2020

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