This is a parametric bash script that you can set up to run at startup or as a cron job in each one of your server.
Each time the server will boot up or execute the script an automatic API call will be created to create if not existent, or update if necessary the related DNS record hosted on Rackspace Cloud.
Please refer to:
http://docs.rackspace.com/cdns/api/v1.0/cdns-devguide/content/index.html