What Makes a Cloud - A Cloud - and not just a Datacenter

Cloud computing has emerged recently as a label for a particular type of datacenter. It can be hosted by anyone; an enterprise, a service provider, or a government. I have been thinking, a way to define cloud computing, is to realize that a Cloud is just a special kind of datacenter. We list seven key characteristics which make a large datacenter into a cloud

1. Implement a pool of computing resources and services which are shared amongst subscribers.

2. Charge for resources and services using an “as used” metered and/or capacity based model.

3. Are usually geographically distributed, in a manner which is transparent to the subscriber (unless they explicitly ask for visibility of that).

4. Are automated in that the provisioning and configuration (and de-configuration and un-provisioning) of resources and services occur on the “self service”, usually programmatic request of the subscriber, occur in an automated way with no human operator assistance, and are delivered in one or two orders of seconds.

5. Resources and services are delivered virtually, that is, although they may appear to be physical (servers, disks, network segments, etc) they are actually virtual implementations of those on an underlying physical infrastructure which the subscriber never sees.

6. The physical infrastructure changes rarely. The virtually delivered resources and services are changing constantly.

7. Resources and services may be of a physical metaphor (servers, disks, network segments, etc) or they may be of an abstract metaphor (blob storage functions, message queue functions, email functions, multicast functions, etc). These may be intermixed.

Cloud computing services as defined above are best exemplified by the Amazon Web Services (AWS) or Google AppEngine. Both of these systems exhibit all seven characteristics as detailed above. Various companies are beginning to offer similar services, such as the Microsoft Azure Service, and software companies such as VMware and open source projects such as UCSB Eucalyptus are creating software for building a cloud service. Each of these offerings embody cloud computing with a self-contained set of conventions, file formats, and programmer interfaces. If one wants to utilize that variation of cloud, one must create configurations and code specific to that cloud.