Continuity

NOTE: this has a decent amount of test coverage, but has yet to be tested in any kind of production environment. I hope to do some more real-worldish testing soon.

Allows you to share scheduling duties across any number of workers. Unlike other solutions (clockwork/rufus-scheduler) it doesn't introduce a single point of failure rely by relying on a single, always running scheduling process. Workers use Redis to coordinate scheduling duties. The scheduler will never miss a job, even if all workers are shut down for a period of time it will pick up from where it left off

Continuity only runs one job at a time, so your tasks should create jobs in Resque, DJ, etc and not actually do the heavy lifting themselves.

Redis could conceivably be replaced by any consistent datastore.

Example

scheduler = Continuity::Scheduler.new_using_redis(redis_handle)

scheduler.every('10s') do
  Resque.enqueue(PeriodicJob)
end

scheduler.cron('0 0 * * * *') do
  Resque.enqueue(DailyJob)
end

scheduler.cron('0 * * * *') do
  Resque.enqueue(DailyJob)
end

# main worker loop
loop do
  do_job
  scheduler.maybe_schedule
end

Cron

• Supports a sixth field at the front for seconds.
• It doesn't support month/day names, use the numeral.
• In many cron implementations entries specifying the day of the month and day of the week (i.e. "0 0 11 1,5 * mon") have a special meaning, this is not supported.

On Schedule Hook

scheduler.on_schedule do |range|
  delayed_jobs = $redis.zrangebyscore(:delayed_jobs, range.first, range.last)
  delayed_jobs.each do |job|
    do_it(job)
  end
end

Re-Entrant Scheduling

Continuity is re-entrant by default. IE, if a job is scheduled to happen at noon and the process is terminated at 11:55 and restarted at 12:05, the job will still be scheduled.

If this is not what you want, you can turn off re-entry by setting :reentrant => false when you create the scheduler. If you do this, continuity will not attempt to schedule any jobs that would have been scheduled more than lookback seconds ago, which defaults to 60.

scheduler = Continuity::Scheduler.new_using_redis(redis_handle, :reentrant => false, :lookback => 5.minutes)

Keep in mind that lookback is process-specific, so you could end up with different processes scheduling for different time ranges the first time they execute.

Contributing to continuity

• Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet
• Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it
• Fork the project
• Start a feature/bugfix branch
• Commit and push until you are happy with your contribution
• Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
• Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.

Copyright

Copyright (c) 2013 Bob Potter. See LICENSE.txt for further details.