Virtualization
While it is possible to lease an entire physical server from most CSPs, this is not the typical use of the cloud. Typically in a public or private cloud the flexibility and better alignment of cost with load comes from the CSP’s ability to distribute the overall workload to particular servers on a mix and match basis implemented at their discretion. The net result of this is that the user has little control over what physical server is used to run their workload and who they share this physical server with and virtualization is the key to making this happen. From a security perspective there have been few if any successful attacks on the industry standard hyper visors that allow multiple virtual servers/users to share one physical server. The discomfort that organizations feel about the situation where they share a physical server with anyone who has a credit card remains and the prospect of this changing in the future is not good. The compliance organizations to which many organizations must report are also uncomfortable with this situation and have been slow to issue guidelines around in-scope data being processed and stored in the cloud.