recurrent
=========


A redis-backed manager of recurrent jobs, for node.js.

(immature, with minimal testing and probably nasty bugs)

Features
--------

* multiple queues, backed up by redis
* tasks have a permanent unique id and mutable associated data
* failed job runs are retried until they succeed or give up, with exponential back-off
* job retries and repetitions don't pile up
* the worker's job implementation determines at the end of each run when (and whether) to repeat
* as many worker processes as you want spread over multiple cores and machines - but you have to start them

Caveats
-------

* single point of failure in queue manager (as well as redis itself) - you need to make sure it stays up / restarts quickly and there's exactly 1 instance

Installing
----------

npm install recurrent

Running the manager
-------------------

Make sure redis is running and then:

var recurrent = require('recurrent');
// will manage a queue q
var m = new recurrent.Manager('q').connect();
pass arguments for redis.createClient() to connect()

recurrent offers a (currently very incomplete) web UI:

http.createServer(m.webUI).listen(7654);

And then browse to localhost:7654

When the manager is not needed anymore:

m.stop()

Starting a recurrent job
------------------------

var recurrent = require('recurrent');
// starts a job which will run for the first time in about 30s
var c = new recurrent.Client('q').connect();
pass arguments for redis.createClient() to connect()
c.add('t1', new Date().getTime() + 30000, {my: 'data'}, function(err) {
  ...
});

Adding again the same taskId will reset execution time.

When the client is not needed any more:

c.stop();

Recurrent job workers
---------------------

var recurrent = require('recurrent');
function doWork(task, cb) {
  // do nothing for 600s
  console.log('got', task.id, 'with this data: ', task.data);
  setTimeout(function () {
    console.error('completed', task.id);
    // do again in about 5s
    cb(null, new Date().getTime()+ 5000);
  }, 600);
}
var w = new recurrent.Worker('q', doWork).connect();
pass arguments for redis.createClient to connect()

When the job worker is not needed any more:

w.stop();

Task failure
------------

Workers must not throw.

To signal failure a worker calls back with error.
It can specify a retry time:

cb('something went wrong', new Date().getTime()+ 1000); // retry in 1s

Or let recurrent do exponential back-off

cb('something went wrong');

Exponential back-off can be configured per worker:

var w = new recurrent.Worker('q', doWork, {
  minBackOff: 500, //  start backing off at 500 ms
  maxBackOff:5000, // max back-off of 5 s
  backOffMultiplier:1.5 // back-off 50% longer every time
}).connect();

When a task is being retried after failure task.retries contains how many retries have been attempted (including the current one).
It will undefined for the first execution, 1 for the first retry and so on.