Distributed Scheduler in Ruby, RoR-3

I'm looking for a RoR scheduler. I am on Rails 3 and can't easily migrate to Rails 4 thanks to our ActiveAdmin customisations. We need a scheduler, and it needs to run on a distributed environment. Don't want to have a single point of failure. Something that uses a database backed locking mechanism will work for us. Don't want to maintain a Redis cluster. We've been on Heroku, and are moving to AWS Opsworks. So looking for a suitable scheduler that can either run as a daemon or be made into one using daemons-rails and run as a separate Opsworks layer.

So far I've tried allora and plashchynski/crono. One requires redis, other requires rails 4. Minimal operational overhead is a priority, and want to avoid maintaining a separate cluster (like redis or zookeeper). Something that easily integrates with Opsworks would be nice.

Thanks in Advance.