percolate:synced-cron

A simple cron system for Meteor. It supports syncronizing jobs between multiple processes. In other words, if you add a job that runs every hour and your deployment consists of multiple app servers, only one of the app servers will execute the job each time (whichever tries first).

Installation

$ meteor add percolate:synced-cron

API

Basics

To write a cron job, give it a unique name, a schedule an a function to run like below. SyncedCron uses the fantastic later.js library behind the scenes. A Later.js parse object is passed into the schedule call that gives you a huge amount of flexibility for scheduling your jobs, see the documentation.

SyncedCron.add({
  name: 'Crunch some important numbers for the marketing department',
  schedule: function(parser) {
    // parser is a later.parse object
    return parser.text('every 2 hours');
  }, 
  job: function() {
    var numbersCrunched = CrushSomeNumbers();
    return numbersCrunched;
  }
});

To start processing your jobs, somewhere in your project add:

SyncedCron.start();

Advanced

SyncedCron uses a collection called cronHistory to syncronize between processes. This also serves as a useful log of when jobs ran along with their output or error. A sample item looks like:

{ _id: 'wdYLPBZp5zzbwdfYj',
  intendedAt: Sun Apr 13 2014 17:34:00 GMT-0700 (MST),
  finishedAt: Sun Apr 13 2014 17:34:01 GMT-0700 (MST),
  name: 'Crunch some important numbers for the marketing department',
  startedAt: Sun Apr 13 2014 17:34:00 GMT-0700 (MST),
  result: '1982 numbers crunched'
}

Call SyncedCron.nextScheduledAtDate(jobName) to find the date that the job referenced by jobName will run next.

Call SyncedCron.remove(jobName) to remove and stop running the job referenced by jobName.

Call SyncedCron.stop() to remove and stop all jobs.

Configuration

Modify the object SyncedCron.options to set configuration entries. Defaults are:

  SyncedCron.options = {
    //Log job run details to console
    log: true,

    //Name of collection to use for synchronisation and logging
    collectionName: 'cronHistory',

    //Default to using localTime
    utc: false, 

    //TTL in seconds for history records in collection to expire
    //NOTE: Unset to remove expiry but ensure you remove the index from 
    //mongo by hand
    //
    //ALSO: SyncedCron can't use the `_ensureIndex` command to modify 
    //the TTL index. The best way to modify the default value of 
    //`collectionTTL` is to remove the index by hand (in the mongo shell 
    //run `db.cronHistory.dropIndex({startedAt: 1})`) and re-run your 
    //project. SyncedCron will recreate the index with the updated TTL.
    collectionTTL: 172800
  }

Caveats

Beware, SyncedCron probably won't work as expected on certain shared hosting providers that shutdown app instances when they aren't receiving requests (like Heroku's free dyno tier or Meteor free galaxy).

Contributing

Write some code. Write some tests. To run the tests, do:

$ meteor test-packages ./

License

MIT. (c) Percolate Studio

Synced Cron was developed as part of the Verso project.