Select unique minutes for a crontab job based on the job and host name ...

unique_crontab_minutes.rb

require 'md5'

#
# unique_crontab_minutes.rb
#

module Puppet::Parser::Functions
  newfunction(:unique_crontab_minutes, :type => :rvalue) do |arguments|

    raise(Puppet::ParseError, "Wrong number of arguments " +
      "given (#{arguments.size} for 2)") if arguments.size < 2

    job_name = arguments[0]
    host     = arguments[1]

    #
    # Pick a random number based on the job and host name.  This will yield
    # the same value for exactly the same combination of the job and host name.
    #
    value = MD5.new(job_name + host).to_s.hex % 60

    # Minutes are from 0 to 59 inclusive ...
    value = value < 60 ? value : 59

    return value
  end
end

# vim: set ts=2 sw=2 et :

"unique" in function name suggest it will not repeat for any other job_name + host (arguments) combination. You can't guarantee that, even if count(hosts) <= 60 there is no way to tell if any other arguments combination won't produce same result.

So either save job_name+host:value to some file and check before return or change name to something like "stateful_crontab_minutes" as it will give same minutes each time puppet is run.

I do agree concerning the unfortunately name of the function, heheh :-) This is an easy fix. But what I do not like, is the idea of storing a file on the side as this is not the best approach when it goes to using Puppet. Hence this simple solution I came up with. Let me look into what can be done better...

well, saving in files have one advantage: you can manually reschedule any or some of hosts to do cron runs earlier than other and it's as simple as:

echo 1 > ns.master.state
echo 10 > ns.slave.state
# when *.state stores minutes

Look at this https://gist.github.com/868080