proletariat

An easy-to-use job queuing and distribution system made in/for node. It supports priorities and priority based `QoS'.

npm install proletariat
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proletariat: distributed job processing on node.js made simple

proletariat is an easy-to-use and distributed job processing software made in node.js.

Installing

npm install proletariat

Running manager

Running supplied manager:

node node_modules/proletariat/bin/manager.js

Making your own manager daemon:

var
    Manager = require('proletariat').Manager,
    manager = new Manager();

// Start
manager.start();

Manager support this options:

AVAIL_THRESHOLD is the number of available slots that manager needs to have after getting full, for distributing work again. Default: 50

CLEANUP_REQS is the number of finished jobs that the system needs to perform for running the cleanup routine. Default: 1000

CLEANUP_CHECKINT is the interval of time (ms) for running the cleanup routine (in case of having empty working queue). Default: 60000

DISTRIB_RANDMAX is the maximum number of ms for waiting before distributing work (this will give time for getting new free slots). Default: 100

DEBUG is for showing or hidding debug messages. Default: false.

SACRED_GUARANTEES is for when you are using guaranteed priority slots, choosing to strictly respected guaranteed in case of having too much high priority jobs.

HOLDSIMILARWORK is for holding tasks with the same _key property value of a running task. When the running task finishes, the result will be sent to the holding tasks. On this way we can avoid similar tasks to run at the same time.

Running workers

Create a new worker file and run it (multiple instances of it, if you want):

var
    Worker = require('proletariat').Worker,
    worker = new Worker({slots: 100, host: "127.0.0.1"});

// Start it
worker.start();

// New work arrive
worker.on('work',function(w,handler){
    // This will take time
    setTimeout(function(){
        handler(null,"Greetings, comrade!");
    }, 1000);
});

Worker support this options:

slots is the number of work slots that this worker will hold. Default: 100

host is the address of the machine where the manager is running. Default: 127.0.0.1

port is the port where the manager is binding on. Default: 1917

prioritySlots is for defining guarantees for ranges of priorities. Default: { 0: value_of_slots_option }

CLEANUP_REQS is the number of finished jobs that the system needs to perform for running the cleanup routine. Default: 1000

CLEANUP_CHECKINT is the interval of time (ms) for running the cleanup routine (in case of having empty working queue). Default: 60000

CON_RETRYTIME is the time (ms) for waiting before reconnecting to server. Default: 2000

ANSWER_THRESHOLD is the number of work answers to keep in memory before answering to server. Default: 1.

Running a client and pushing work

Create a new client file and run it:

var
    Proletariat = require('proletariat').Client,
    proletariat = new Proletariat("127.0.0.1");

proletariat.work([{some:"work"}],{timeout: 60000, priority: 1},function(err,res){
    if ( err ) {
        console.log("Fail at work: ",err);
        return;
    }

    console.log("Result: ",res);
});

Client support this options:

host is the address of the machine where the manager is running. Default: 127.0.0.1

port is the port where the manager is binding on. Default: 1917

and this methods:

work(workGroup,options,finishCallback) for pushing a work or a work group. Supported options are: timeout, runTimeout, assigntimeout and priority.

workIndividual(workGroup,options,workCallback,groupCallback) for pushing a work group and calling workCallback for each finished work and groupCallback when all the work group has finished. Options are the same as for work().

How does it work ?

Architecture

From top to bottom:

Clients just connect to the manager, push some works and wait for the answer.

Manager receives connections from clients and workers. If the client makes an offer (work force) he's then called a worker. It the client pushes some work, he will be treated as a simple client. When a client pushes some work, it will be registered on a specific queue, according to the work's priority and then, when possible, will be assigned to an available worker. When the worker finishes doing that task, answers to the manager, who sends it back to the client.

Assigning

The default work->worker assigning function tends to balance the workload on all the workers, being more probable to assign a task to a free worker than a busiest one. Anyway, being the function based on Math.random(), something else can happen.

Some systems may need to implement their own assigning function. Example:

manager.workSelectWorker = function(work,workers,totalAvailable) {

        var
                comrades = Object.keys(workers);

        return this.workers[comrades[parseInt(Math.random()*comrades.length)]];

};

// Start

manager.start();

Timeouts

Client-side/Global timeout

client.work() and client.workIndividual() support specifying a timeout option, in milliseconds, which will limit the global available time (pushing to manager, assigning, running, ..., returning) for the work(s). It starts counting on the moment that client.work() or client.workIndividual() are called. If the running time exceeds the timeout value, the error { code: "ECSTO" } will be returned.

Running timeout

client.work() and client.workIndividual() support specifying a runTimeout option, in milliseconds, which will limit the running time of the work(s). It starts counting at the same moment that the work(s) start running on the worker. If the running time exceeds the runTimeout value, the error { code: "ETO" } will be returned.

Assigning timeout

client.work() and client.workIndividual() support specifying an assigntimeout option, in milliseconds, which will limit the time taken for assigning the work(s) to a worker. If the manager takes more than the specified time to assign these works to a worker, the error { code: 'EATO' } will be returned to the client and an assigntimeout event will be emitted on the manager.

Priorities and guarantees

client.work() and client.workIndividual support specifying a priority for the work or work group. High priority works will be firstly assigned to the workers when they have available slots, however, without guarantees that they will be immediatelly assigned.

For having guarantees that high priority tasks will have available slots, you should play with the prioritySlots and slots options on the worker(s). The prioritySlots option will allow us to define priority ranges and set a number of guaranteed slots for each range.

Example: Setting slots number to 100 and prioritySlots to {1:30,2:20} will define the limit of 50 simultaneous works with priority >= 0 and < 1, 80 to works with priority >= 1 and < 2 and 100 to works with priority >= 2. This rules will guarantee that low priority works will never run out of certain limits, keeping space for high priority works.

But, if you were paying attention, you could notice that high priority tasks can still take all the system slots, even stealing the "guaranteed" slots of lower priority ranges. Using the case of last example, you can't be sure that works with priority of 2 will not take the "guaranteed" space for works with priority >= 1 and < 2.

For keeping this guarantees, you should set the manager option SACRED_GUARANTEES to true. This will make sure that if higher priority works will start going out of their guaranteed space, they will only steal slots from the lowest priority range (usually the range >= 0), saving the other guarantees. Again, using the example, but now setting manager SACRED_GUARANTEES to true, we will be defining the limit of 50 to works with priority >= 0 and < 1, 80 to works with priority >= 1 and < 2 and 70 to works with priority >= 2.

System messages

Clients and workers support sending system messages to the manager and to all other clients and workers by using systemMessage(msg[,opts,callBack]) method. The supplied message will be sent and sysmsg event will be fired on the manager and/or on all the clients/workers. The callBack function will be called only when all the recipients get the message.

systemMessage() supported options:

to - The destination of the message. The supported destinations are: MANAGER - for sending only to the manager process; null - for sending to everybody; an available client ID - for sending just to a specific client or worker.

Example (manager):

manager.on('sysmsg',function(msg){
   console.log("System message: ",msg);
});

Example (worker):

worker.systemMessage({"do":"something"},{},function(){
   console.log("Everybody got the message");
});
worker.on('sysmsg',function(msg){
   console.log("System message: ",msg);
});

Example (client):

client.systemMessage({"do":"something"},function(){
   console.log("Everybody got the message");
});

Multiprocessor

On the current state, the three components of proletariat are single threaded. However, you can launch how many worker processes as you wish, making better use of multiprocessor machines.

In the future, the manager process will naturally support running on multiple processes at the same time.

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