We're going to use Cloud Databases for our setup because it's more secure, and performance has been shown to be over 200% faster than Amazon RDS!
Each Cloud Databases instance is given a private IP address. This restricts access to it from within the Rackspace network. While your Cloud Server can make a connection to the database, the outside world cannot.
Further information on “Private vs Public access to Cloud Databases” can be found in the following Knowledge Center Article: Public Vs. Private Access