recluster

Clustering library with support for zero-downtime reloading

npm install recluster
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recluster

Clustering library with support for zero-downtime reloading

usage

If server.js is your regular http server (e.g. express), create cluster.js and add:

var recluster = require('recluster'),
    path = require('path');

var cluster = recluster(path.join(__dirname, 'server.js'));
cluster.run();

process.on('SIGUSR2', function() {
    console.log('Got SIGUSR2, reloading cluster...');
    cluster.reload();
});

console.log("spawned cluster, kill -s SIGUSR2", process.pid, "to reload");

then run it

node cluster.js

To hot-reload the server, simply run

kill -s SIGUSR2 <cluster_pid>

To find out which of the N (= number of cores by default) worker instances you're running from inside server.js, you can use

process.env.WORKER_ID

which is zero-based i.e. 0 <= WORKER_ID < N

options

var cluster = recluster(file, opt)

where

file

Absolute path to the module that defines the server

opt.workers

Number of active workers (default = cores)

opt.timeout

Timeout to kill old workers after reload (seconds).

Defaults to 1 second in development, 1 hour in production.

opt.respawn

Minimum time between worker respawns when workers die (seconds)

opt.backoff

Maximum respawn time (reached via exponential backoff). Set to 0 or undefined to disable exponential backoff.

opt.readyWhen

Use 'listening' for servers (e.g. for express/connect http servers) and 'started' for workers that are immediately ready.

If you want to manually tell recluster when the worker is ready to replace older workers you can use {readyWhen: 'ready'}. Then, to signal readiness from the worker use process.send({cmd: 'ready'})

opt.log

Log various events to stdout. Currently only 'respawns' is supported. Default: {respawns: true}

cluster

The returned object has the following methods:

cluster.run

Starts the cluster by running child processes

cluster.reload

Hot-reloads new code. some of the children will remain active for opt.timeout seconds after reload

cluster.terminate

Terminates the entire cluster and removes all listeners.

worker cleanup

A server worker can gracefully exit by cleaning up in the 'close' event of its server:

server.on('close', function() { 
    // cleanup 
});

Non-server workers can listen for the disconnect command and shut down gracefully before the kill timeout:

process.on('message', function(m) { 
    if (m.cmd == 'disconnect') { 
        // cleanup 
    }
})

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