Issue with rufus-scheduler when we have multiple EC2 instances

Question

I have deployed rails app on two EC2 instances. I have scheduled on Job with rufus-scheduler to run every 24 hours to send some emails.

But scheduler is running separately on two instances.

I need run scheduler on only one instance. So can you please help with this issue?

Thanks

Answer 1

Let's assume you've followed https://github.com/jmettraux/rufus-scheduler#so-rails

You could modify the initializer in this way:

#
# config/initializers/scheduler.rb

require 'rufus-scheduler'

s = Rufus::Scheduler.singleton

unless File.exist?(File.dirname(__FILE__) + '/../../no_scheduling')

  s.every '1m' do
    Rails.logger.info "hello, it's #{Time.now}"
  end
end

Then in the Rails root of the instance you don't want to schedule, simply touch the no_scheduling file, then start your Rails. The instances with a "no_scheduling" file will not schedule.

Exercise 1: enhance the initializer above so that it doesn't even instantiate the scheduler if no_scheduling is present.

Exercise 2: replace the file check by an IP check so that only the rails setup on a given IP schedules.