An HTTP request duplicator using node.js

A lot of times we feel the need to duplicate a request to multiple servers or ports maybe because the source is one or maybe because we want different actions to be taken on the same request. I had a similar problem where I had multiple servers which were used by different teams and all the teams were expecting a particular request on their VMs. However the problem was that the source of request was single. Thus, there was no option but to develop something to accomplish the above task.

Writing something from scratch in Java/.NET would give me flexibility but would take a lot of time to develop. Then I came across duplicator open source project which I modified to enable it to duplicate the same request to multiple targets.

The source code is hosted at https://github.com/ameyakhasgiwala/multi-duplicator and the single script file can be downloaded or forked if required. I am also pasting the script here for readability

The script can be configured with parameters.
-p: the port on which the script will listen for requests
-f: single -f parameter specifying the VM:port to which the request should be forwarded.
-d: multiple -d parameters specifying the VM:port to which the request should be duplicated.

node /usr/local/bin/multi-duplicator -p 8102 -f server1.myorg:9876 -d server2.otherorg:1234 -d server3.org3:3456

#!/usr/bin/env node

// vim: set ft=javascript:

var cluster = require('cluster')

var colors = require('colors')

var log = console.log.bind(console, '[Cluster]'.blue)

if (cluster.isMaster) {

  var opts = require('optimist')

      .usage('Usage: $0 [-hv] -p port -f host:port [-d host:port] [-r int]')

      .options('h',

        { alias: 'help'

        , describe: 'show usage information'

        })

      .options('v',

        { alias: 'version'

        , describe: 'show version information'

        })

      .options('p',

        { alias: 'port'

        , describe: 'port to listen on, defaults to PORT'

        , 'default': process.env['PORT']

        })

      .options('f',

        { alias: 'forward'

        , describe: 'host to forward to'

        })

      .options('d',

        { alias: 'duplicate'

        , describe: 'host to duplicate to'

        })

      .options('r',

        { alias: 'rate'

        , describe: 'rate to sample traffic'

        , 'default': 1

        })

      .check(function(argv){

        if (argv.h) throw ''

        if (argv.v) {

          console.log(duplicator.version)

          process.exit()

        }

        if (!argv.p) throw 'You must specify a port, either via the -p option or' +

          'in the PORT environment variable'

        if (!argv.f) throw 'You must specify a host to forward to with -f option'

      })

    , argv = opts.argv

  function serverInfo() {

    log("Listening on port:", argv.p)

    if (argv.f) log("Forwarding to:", argv.f)

    if (argv.d) log("Duplicating to:", argv.d)

    if (argv.r) log("Sample rate:", argv.r)

    log(Array.isArray(argv.d))

  }

  var workers = {}

  function spawn(argv) {

    var worker = cluster.fork()

    workers[worker.pid] = worker

    worker.send(argv)

    return worker

  }

  var count = require('os').cpus().length

  for (var i = 0; i < count; i++) {

    spawn(argv)

  }

  serverInfo()

  cluster.on('exit', function(worker) {

    log('worker ' + worker.pid + ' died. spawning a new process...')

    delete workers[worker.pid]

    spawn(argv)

  })

} else {

  var duplicator = require('../')

  log = console.log.bind(console, '[Worker]'.green)

  process.on('message', function(argv) {

    log('worker started with pid', process.pid)

    var server = duplicator(function(client, forward, duplicate) {

      if (argv.f) forward(argv.f)

      if (argv.d) {

        if (Array.isArray(argv.d)) {

          argv.d.forEach (function(dup) {

            log("duplicating request to", dup)

            duplicate(dup, argv.r)

          })

        }

        else {

          duplicate(argv.d, argv.r)

        }

      }

    })

    server.listen(argv.p)

  })

}