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sticky-listen

A simple performant way to use socket.io with recluster, based on Fedor's sticky-session

Installation

npm install sticky-listen

Usage

In your cluster.js that uses recluster, use sticky.createBalancer to create a sticky balancing server.

var recluster = require('recluster'),
    path = require('path'),
    sticky = require('sticky-listen')

var cluster = recluster(path.join(__dirname, 'server.js'), {
  readyWhen: 'ready'
});

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");

// Added for the sticky listener:

var balancer = sticky.createBalancer({
  behindProxy: false,
  activeWorkers: cluster.activeWorkers,
  maxRetries: 5,
  retryDelay: 100
});

balancer.listen(8081, function() {
  console.log("Sticky balancer listening on port", 8081);
});

In your server.js, use sticky.listen instead of server.listen to start the server, then use process.send({cmd: 'ready'}) to indicate that the worker is ready.

var sticky = require('sticky-listen');

var server = require('http').createServer(function(req, res) {
  res.end('worker: ' + process.env.NODE_WORKER_ID);
});

sticky.listen(server)

process.send({cmd: 'ready'})

Acknowledgement

This module is based on Fedor Indutny's sticky-session, but it decouples the worker management logic, enabling you to use any cluster library (such as recluster). The only requirement is that createBalancer needs to be passed activeWorkers, a function that returns a hash containing

  • a field length, the number of worker slots that serve requests
  • for every key 0..length, a field that contains a worker object of a worker that is capable of receiving new connections. If a worker isn't ready at that slot, the field should be null

API

sticky.listen(server)

For use from the worker process

Listens for sticky connections from a worker server. The port doesn't need to be specified.

sticky.createBalancer(options)

For use from the master process

Creates a new master balancer server that balances between worker servers.

Returns a regular net.Server. Call server.listen(port) to start listening for connections and balancing those connections across the cluster.

Sticky sessions are achieved based on the IP address of the client - requests from the same IP are redirected to the same worker index.

The available options are

activeWorkers

A function that returns a hash of the worker slots. For recluster based balancers that would be cluster.activeWorkers. The hash should contain:

  • a field length, the number of worker slots that serve requests
  • for every key 0..length, a field that contains a worker object of a worker that is capable of receiving new connections. If a worker isn't ready at that slot, the field should be null
retryDelay

If there are no worker available to serve the client, retry finding one after retryDelay miliseconds.

maxRetries

The number of retries to attempt before giving up and sending a 502 Bad Gateway error to the client.

behindProxy

If you use this option, sticky-listen will read the headers and look for x-forwarded-for when reading the IP address of the client. This enables the balancer to work well even behind proxies such as HAProxy or nginx.

LICENSE

This software is licensed under the MIT License.

Copyright Fedor Indutny and Gorgi Kosev, 2015

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.