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cluster-magic

run multi-threaded node.js network applications using the native cluster module

Features

  • Run network applications within multiple processes multiplexed by node.js
  • Easy to use, configless
  • Standalone, no external process managers required
  • Respawn dead/failed workers
  • Gracefull application shutdown via sigterm
  • Hot-Reload/Hot-Restart via sighup
  • Delayed restart of failed processes to avoid infinite restart loops

Install

$ npm install cluster-magic --save
$ yarn add cluster-magic

Usage

A working snippet is available in the examples directory. Just run node examples/startup.js

File: startup.js

Initializes the cluster application

const _cluster = require('cluster-magic');
const _app = require('./application.js');

// start the clustered app (8 workers)
_cluster.init(_app, {
    numWorkers: 8
});

File: application.js

Your socket based application which should be multiplexed

const net = require('net');

function startup(){
    const server = net.createServer((socket) => {
        // connections never end
    });
    
    server.listen(8000);
}

module.exports = {
    // init hook
    init: startup
};

Hot-Restart / Hot-Reload

To hot-restart (zero downtime) an application, just send a SIGHUP to the master process. This spawns new workers and disconnects all current workers from the cluster-proxy

Example

# send SIGHUP to process 12345
kill -HUP 12345

Signals

  • SIGHUP Restart workers
  • SIGTERM Gracefull application shutdown
  • SIGINT Gracefull application shutdown

Delayed Restarts

cluster-magic comes with as simple delayed-restart policy which suppresses infinite restart loops.

  • In case a process dies, an internal counter will be incremented.
  • If a threshold of 10 is reached the process restart is delayed by counter*200ms to avoid infinite restart loops on internal application errors. Well..this is may not what you expect from a "clustered application" but such an error requires that a manual fix will take place by the operations team (_logger.alert event is triggerd which SHOULD be observed)
  • The counter is decremented by 1 once per minute.

Environment

To specify the number of workers you can easily pass the environment variable NUM_WORKERS to the nodejs process. Default is set to num_cpus*2

License

cluster-magic is OpenSource and licensed under the Terms of The MIT License (X11) - your're welcome to contribute