Note the following known limitations when using CloudStack with RightScale.
Uploading CentOS 5.5+ images to CloudStack 2.2 - There is a known limitation when uploading CentOS 5.5 (or later) images to a CloudStack 2.2 private cloud. The XenServer 5.6 GA hypervisor does not recognize the CentOS 5.5 OS Type and the image will fail to boot. To work around this issue, upload the image with an OS Type of "Other PV (64-bit)" or "CentOS 5.4 (64-bit)".
Uploading CentOS 5.6 images to CloudStack 3.0 - There is a known limitation when uploading CentOS 5.6 images to a CloudStack 3.0 private cloud. You must set the image to use CentOS 5.5 OS type on CloudStack 3.0.