function to gradually deploy using puppet

gradual_deploy.rb

module Puppet::Parser::Functions
  newfunction(:gradual_deploy, :type => :rvalue, :arity => 4, :doc => "\
    Gradually deploy something
    Arguments are from, to, start and finish. Will gradually move from returning <from>
    to returning <to> over the duration between <start> and <finish>.
    start and finish are specified as ruby datetime strings, supports all formats that ruby
    can parse.
    ") do |args|
    from, to, start, finish = *args

    require 'date'

    start = DateTime.parse(start)
    finish = DateTime.parse(finish)

    # Duration of deploy in seconds
    duration = ((finish-start)*86400).to_i

    Puppet::Parser::Functions.function('fqdnrand')
    if start+(function_fqdnrand(duration).to_r/86400) > DateTime.now then
      return to
    else
      return from
    end
  end
end