There has been plenty of disagreement over the last few years about what constitutes ‘Cloud Computing’. Nevertheless, a growing number of public and private services prove its existence, if not its exact character, and pronouncements by impartial groups such as NIST adds clarity to the discussion—for those who find that to be an advantage!

Attempts to characterize Cloud have primarily focused on breaking it into three different levels of abstraction, and on defining whether it is a public or privately operated service.

For example:

  1. Public Infrastructure As A Service: Amazon, Rackspace and many others,
  2. Public Platform As A Service: Google App Engine, Windows Azure, vmForce and Heroku,
  3. Public Software As A Service: Salesforce and a cast of thousands

A Cloud Computing service always contains four vital elements: services-orientation, utility pricing, elasticity, and delivery over the Internet. NIST consider location transparent resource pooling to also be a requisite feature, although that is somewhat implied by the Internet delivery model.

Ultimately it does not mean server consolidation or automation. It’s a fundamental rethink of the IT stack, as well as the processes that deliver services to internal and external customers.

There are also differences of opinion over the benefits and drawbacks of public cloud versus private cloud, and whether certain types of system or workload are unsuited to the cloud model in any incarnation. However, despite the disagreements few would dispute that Cloud is the current big shake up in a field who’s relatively brief history has been one disruption after another.