Rubber Capistrano Task to create CNAME records for app hosts

rubber_cname.rb

# uses route53 gem https://github.com/pcorliss/ruby_route_53

namespace :rubber do 
    desc "Setup Route53 for hosts"
    task :setup_route53 do
      require 'route53'
      conn = Route53::Connection.new("ACCESS_KEY","SECRET_ACCESS_KEY")
      #List Operations
      zones = conn.get_zones #Requests list of all zones for this account
      records = zones.first.get_records #Gets list of all records for a specific zone
      # puts records
      # puts records[0].type
      cnames = []
      records.each do |record|
         cnames << record.name if record.type == 'CNAME'
      end
      # puts cnames     
      app_servers = rubber_instances.for_role("app")
      puts "App Servers on #{RUBBER_ENV}" 
      app_servers.each do |instance|                 
        unless cnames.include?("#{instance.name}.#{instance.domain}.")
          # puts "\t#{instance.name}.#{instance.domain}" 
          # puts instance.external_host
          new_record = Route53::DNSRecord.new("#{instance.name}.#{instance.domain}","CNAME","120",["#{instance.external_host}"],zones.first)
          new_record.create
          sleep 5
        end
      end
    end 
end

I believe this task should run after an instance is created or deleted. Any pointers on how to run this?