node-resque

node-resque

Delayed Tasks in nodejs. A very opinionated but compatible API with resque and resque scheduler

Usage

I learn best by examples:

/////////////////////////
// REQUIRE THE PACKAGE //
/////////////////////////

var NR = require("node-resque");

///////////////////////////
// SET UP THE CONNECTION //
///////////////////////////

var connectionDetails = {
  host:      "127.0.0.1",
  password:  "",
  port:      6379,
  database:  0,
}

//////////////////////////////
// DEFINE YOUR WORKER TASKS //
//////////////////////////////

var jobs = {
  "add": {
    perform: function(a,b,callback){
      var answer = a + b;
      callback(null, answer);
    },
  },
  "subtract": {
    perform: function(a,b,callback){
      var answer = a - b;
      callback(null, answer);
    },
  },
  "multiply": function(a,b,callback) {
    callback(null, a * b);
  },
};

////////////////////
// START A WORKER //
////////////////////

var worker = new NR.worker({connection: connectionDetails, queues: ['math']}, jobs, function(){
  worker.workerCleanup(); // optional: cleanup any previous improperly shutdown workers on this host
  worker.start();
});

///////////////////////
// START A SCHEDULER //
///////////////////////

var scheduler = new NR.scheduler({connection: connectionDetails}, function(){
  scheduler.start();
});

/////////////////////////
// REGISTER FOR EVENTS //
/////////////////////////

worker.on('start',           function(){ console.log("worker started"); })
worker.on('end',             function(){ console.log("worker ended"); })
worker.on('cleaning_worker', function(worker, pid){ console.log("cleaning old worker " + worker); })
worker.on('poll',            function(queue){ console.log("worker polling " + queue); })
worker.on('job',             function(queue, job){ console.log("working job " + queue + " " + JSON.stringify(job)); })
worker.on('reEnqueue',       function(queue, job, plugin){ console.log("reEnqueue job (" + plugin + ") " + queue + " " + JSON.stringify(job)); })
worker.on('success',         function(queue, job, result){ console.log("job success " + queue + " " + JSON.stringify(job) + " >> " + result); })
worker.on('failure',         function(queue, job, failure){ console.log("job failure " + queue + " " + JSON.stringify(job) + " >> " + failure); })
worker.on('error',           function(queue, job, error){ console.log("error " + queue + " " + JSON.stringify(job) + " >> " + error); })
worker.on('pause',           function(){ console.log("worker paused"); })

scheduler.on('start',             function(){ console.log("scheduler started"); })
scheduler.on('end',               function(){ console.log("scheduler ended"); })
scheduler.on('error',             function(error){ console.log("scheduler error >> " + error); })
scheduler.on('poll',              function(){ console.log("scheduler polling"); })
scheduler.on('working_timestamp', function(timestamp){ console.log("scheduler working timestamp " + timestamp); })
scheduler.on('transferred_job',    function(timestamp, job){ console.log("scheduler enquing job " + timestamp + " >> " + JSON.stringify(job)); })

////////////////////////
// CONNECT TO A QUEUE //
////////////////////////

var queue = new NR.queue({connection: connectionDetails}, jobs, function(){
  queue.enqueue('math', "add", [1,2]);
  queue.enqueue('math', "add", [2,3]);
  queue.enqueueIn(3000, 'math', "subtract", [2,1]);
});

Configuration Options:

new queue requires only the "queue" variable to be set. You can also pass the jobs hash to it.

new worker has some additonal options:

options = {
  looping: true,
  timeout: 5000,
  queues:  "*",
  name:    os.hostname() + ":" + process.pid
}

The configuration hash passed to new worker, new scheduler or new queue can also take a connection option.

var connectionDetails = {
  package:   "redis",
  host:      "127.0.0.1",
  password:  "",
  port:      6379,
  database:  0,
  namespace: "resque",
}

var worker = new NR.worker({connection: connectionDetails, queues: 'math'}, jobs, function(){
  worker.start();
});

You can also pass redis client directly.

// assume you already initialize redis client before

var connectionDetails = { redis: redisClient }

var worker = new NR.worker({connection: connectionDetails, queues: 'math'}, jobs, function(){
  worker.start();
});

Notes

• Be sure to call worker.end() before shutting down your application if you want to properly clear your worker status from resque
• When ending your application, be sure to allow your workers time to finish what they are working on
• If you are using any plugins which effect beforeEnqueue or afterEnqueue, be sure to pass the jobs argument to the new Queue constructor
• If a job fails, it will be added to a special failed queue. You can then inspect these jobs, write a plugin to manage them, move them back to the normal queues, etc. Failure behavior by default is just to enter the failed queue, but there are many options. Check out these examples from the ruby ecosystem for insperation:
  • https://github.com/lantins/resque-retry
  • https://github.com/resque/resque/wiki/Failure-Backends
• If you plan to run more than one worker per nodejs process, be sure to name them something distinct. Names must follow the patern hostname:pid+unique_id. For example:

var name = os.hostname() + ":" + process.pid + "+" + counter;
var worker = new NR.worker({connection: connectionDetails, queues: 'math', 'name' : name}, jobs);

Queue Managment

Additonal methods provided on the queue object:

• queue.prototype.queues = function(callback)
  • callback(error, array_of_queues)
• queue.prototype.delQueue = function(q, callback)
  • callback(error)
• queue.prototype.queued = function(q, start, stop, callback)
  • callback(error, jobs_in_queue)
• queue.prototype.length = function(q, callback)
  • callback(error, number_of_elements_in_queue)
• queue.prototype.del = function(q, func, args, count, callback)
  • callback(error, number_of_items_deleted)
• queue.prototype.delDelayed = function(q, func, args, callback)
  • callback(error, timestamps_the_job_was_removed_from)
• queue.prototype.scheduledAt = function(q, func, args, callback)
  • callback(error, timestamps_the_job_is_scheduled_for)

Delayed Status

• queue.timestamps = function(callback)
  • callback(error, timestamps)
• queue.delayedAt = function(timestamp, callback)
  • callback(error, jobs_enqueued_at_this_timestamp)
• queue.allDelayed = function(timestamp)
  • callback(error, jobsHash)
  • jobsHash is an object with its keys being timestamps, and the vales are arrays of jobs at each time.
  • note that this operation can be very slow and very ram-heavy

Worker Status

You can use the queue object to check on your wokrers:

• queue.workers = function(callback)`
  • returns: { 'host:pid': 'queue1, queue2', 'host:pid': 'queue1, queue2' }
• queue.workingOn = function(workerName, queues, callback)`
  • returns: {"run_at":"Fri Dec 12 2014 14:01:16 GMT-0800 (PST)","queue":"test_queue","payload":{"class":"slowJob","queue":"test_queue","args":[null]},"worker":"workerA"}
• queue.allWorkingOn = function(callback)`
  • returns a hash of the results of queue.workingOn with the worker names as keys.

Failed Job Managment

From time to time, your jobs/workers may fail. Resque workers will move failed jobs to a special failed queue which will store the original arguments of your job, the failing stack trace, and additional medatadata.

You can work with these failed jobs with the following methods:

• queue.failedCount = function(callback)

  • callback(error, failedCount)
  • failedCount is the number of jobs in the failed queue

• queue.failed = function(start, stop, callback)

  • callback(error, failedJobs)
  • failedJobs is an array listing the data of the failed jobs. Each element looks like:

{ worker: 'busted-worker-3',
  queue: 'busted-queue',
  payload: { class: 'busted_job', queue: 'busted-queue', args: [ 1, 2, 3 ] },
  exception: 'ERROR_NAME',
  error: 'I broke',
  failed_at: 'Sun Apr 26 2015 14:00:44 GMT+0100 (BST)' }

• queue.removeFailed = function(failedJob, callback)

  • callback(error)
  • the input failedJob is an expanded node object representing the failed job, retrieved via queue.failed

• queue.retryAndRemoveFailed = function(failedJob, callback)

  • callback(error)
  • the input failedJob is an expanded node object representing the failed job, retrieved via queue.failed
  • this method will instantly re-enqueue a failed job back to its original queue, and delete the failed entry for that job

Failed Worker Managment

Sometimes a worker crashes is a severe way, and it doesn't get the time/chance to notifiy redis that it is leaving the pool (this happens all the time on PAAS providers like Heroku). When this happens, you will not only need to extract the job from the now-zombie worker's "working on" status, but also remove the stuck worker. To aid you in these edge cases, ``queue.cleanOldWorkers(age, callback)` is available.

Because there are no 'heartbeats' in resque, it is imposable for the application to know if a worker has been working on a long job or it is dead. You are required to provide an "age" for how long a worker has been "working", and all those older than that age will be removed, and the job they are working on moved to the error queue (where you can then use queue.retryAndRemoveFailed) to re-enqueue the job.

If you know the name of a worker that should be removed, you can also call queue.forceCleanWorker(workerName, callback) directly, and that will also remove the worker and move any job it was working on into the error queue.

Plugins

Just like ruby's resque, you can write worker plugins. They look look like this. The 4 hooks you have are before_enqueue, after_enqueue, before_perform, and after_perform

var myPlugin = function(worker, func, queue, job, args, options){
  var self = this;
  self.name = 'myPlugin';
  self.worker = worker;
  self.queue = queue;
  self.func = func;
  self.job = job;
  self.args = args;
  self.options = options;
}

////////////////////
// PLUGIN METHODS //
////////////////////

myPlugin.prototype.before_enqueue = function(callback){
  // console.log("** before_enqueue")
  callback(null, true);
}

myPlugin.prototype.after_enqueue = function(callback){
  // console.log("** after_enqueue")
  callback(null, true);
}

myPlugin.prototype.before_perform = function(callback){
  // console.log("** before_perform")
  callback(null, true);
}

myPlugin.prototype.after_perform = function(callback){
  // console.log("** after_perform")
  callback(null, true);
}

And then your plugin can be invoked within a job like this:

var jobs = {
  "add": {
    plugins: [ 'myPlugin' ],
    pluginOptions: {
      myPlugin: { thing: 'stuff' },
    },
    perform: function(a,b,callback){
      var answer = a + b;
      callback(null, answer);
    },
  },
}

notes

• All plugins which return (error, toRun). if toRun = false on beforeEnqueue, the job beign inqueued will be thrown away, and if toRun = false on beforePerfporm, the job will be reEnqued and not run at this time. However, it doesn't really matter what toRun returns on the after hooks.
• If you are writing a plugin to deal with errors which may occur during your resque job, you can inspect and modify worker.error in your plugin. If worker.error is null, no error will be logged in the resque error queue.
• There are a few included plugins, all in the lib/plugins/* directory. You can rewrite you own and include it like this:

var jobs = {
  "add": {
    plugins: [ require('myplugin') ],
    pluginOptions: {
      myPlugin: { thing: 'stuff' },
    },
    perform: function(a,b,callback){
      var answer = a + b;
      callback(null, answer);
    },
  },
}

Multi Worker

node-resque provides a wrapper around the worker object which will auto-scale the number of resque workers. This will process more than one job at a time as long as there is idle CPU within the event loop. For example, if you have a slow job that sends email via SMTP (with low rendering overhead), we can process many jobs at a time, but if you have a math-heavy operation, we'll stick to 1. The multiWorker handles this by spawngning more and more node-resque workers and managing the pool.

var NR = require(__dirname + "/../index.js");

var connectionDetails = {
  package:   "redis",
  host:      "127.0.0.1",
  password:  ""
}

var multiWorker = new NR.multiWorker({
  connection: connectionDetails, 
  queues: ['slowQueue'],
  minTaskProcessors:   1,
  maxTaskProcessors:   100,
  checkTimeout:        1000,
  maxEventLoopDelay:   10,  
  toDisconnectProcessors: true,
}, jobs, function(){

  // normal worker emitters
  multiWorker.on('start',             function(workerId){                      console.log("worker["+workerId+"] started"); })
  multiWorker.on('end',               function(workerId){                      console.log("worker["+workerId+"] ended"); })
  multiWorker.on('cleaning_worker',   function(workerId, worker, pid){         console.log("cleaning old worker " + worker); })
  multiWorker.on('poll',              function(workerId, queue){               console.log("worker["+workerId+"] polling " + queue); })
  multiWorker.on('job',               function(workerId, queue, job){          console.log("worker["+workerId+"] working job " + queue + " " + JSON.stringify(job)); })
  multiWorker.on('reEnqueue',         function(workerId, queue, job, plugin){  console.log("worker["+workerId+"] reEnqueue job (" + plugin + ") " + queue + " " + JSON.stringify(job)); })
  multiWorker.on('success',           function(workerId, queue, job, result){  console.log("worker["+workerId+"] job success " + queue + " " + JSON.stringify(job) + " >> " + result); })
  multiWorker.on('failure',           function(workerId, queue, job, failure){ console.log("worker["+workerId+"] job failure " + queue + " " + JSON.stringify(job) + " >> " + failure); })
  multiWorker.on('error',             function(workerId, queue, job, error){   console.log("worker["+workerId+"] error " + queue + " " + JSON.stringify(job) + " >> " + error); })
  multiWorker.on('pause',             function(workerId){                      console.log("worker["+workerId+"] paused"); })
  
  // multiWorker emitters
  multiWorker.on('internalError',     function(error){                         console.log(error); })
  multiWorker.on('multiWorkerAction', function(verb, delay){                   console.log("*** checked for worker status: " + verb + " (event loop delay: " + delay + "ms)"); })

  multiWorker.start();
});

Presentation

This package was featued heavily in this presentation I gave about background jobs + node.js. It contains more examples!

Acknowledgments

Most of this code was inspired by / stolen from coffee-resque and coffee-resque-scheduler. Thanks!