I continue to talk with clients who understand the concept of private cloud computing, they think they know it when they see it, but they can’t quite explain it in words. A year ago I described The Spectrum of Private to Public Cloud Services, but I didn’t put that in the form of a definition. Here’s a shot.
Gartner’s official definition of cloud computing is “A style of computing where scalable and elastic IT-enabled capabilities are delivered as a service to customers using Internet technologies.” We also describe five defining attributes of cloud computing: service-based, scalable and elastic, shared, metered by use, uses Internet technologies. A key to cloud computing is an opaque boundary between the customer and the provider. Graphically, that looks like this:
When the customer does not see the implementation behind the boundary, and the provider doesn’t care who the customer is, you have a public cloud service. So what is private cloud?
Private cloud is “A form of cloud computing where service access is limited or the customer has some control/ownership of the service implementation.”
Graphically, that means that either the provider tunnels through that opaque boundary and limits service access (e.g., to a specific set of people, enterprise or enterprises), or the customer tunnels through that opaque boundary through ownership or control of the implementation (e.g., specifying implementation details, limiting hardware/software sharing). Note that control/ownership is not the same as setting service levels – these are specific to the implementation, and not even visible through the service.
The ultimate example would be enterprise IT, building a private cloud service used only by its enterprise. But there are many other examples, such as a virtual private cloud (the same as the example above, except replace ‘enterprise IT’ with ‘third-party provider’), and community clouds (the same as a virtual private cloud, except opened up to a specific and limited set of different enterprises).
Still “foggy”, or is it “clear”?