NIST's Cloud Computing Definition and Deployment Models

Of the various definitions of cloud computing floating around, I perceive that the NIST definition is the one most referenced. NIST prescribes 5 essential characteristics of cloud computing, 3 service models and 4 deployment models.

The essential characteristics and the service models are well understood and well accepted. The deployment models deserve some additional discussion.

From an accessibility point of view, the private, community, public and hybrid deployment models share the following structural properties [All cloud deployments are multi-subscriber; multiple users provide the strength of cloud computing economics]:

1. Private clouds are dedicated [to one enterprise], but multi-subscriber [to enterprise's employees and/or partners].
2. Some cloud deployments are multi-tenant and multi-subscriber; most of the public clouds fall into this category. And, one can imagine private clouds hosted on public IaaS clouds.

Now, the four deployment models that NIST prescribes really are specialized instantiations on top of the dedicated & multi-subscriber or multi-tenant & multi-subscriber properties. For example, as NIST definition itself notes, a community cloud can be economically hosted on a public cloud. And, the hybrid clouds include traditional IT implementations in addition to [multi-tenant and] multi-subscriber clouds.

What is the upshot? While multi-subscriber quality is essential for cloud computing, multi-tenancy improves that economics in an orthogonal dimension, and the resulting economics is multiplicative! We need a characterization of cloud platforms based on such orthogonal considerations. Of course, the key for increasing adoption of multi-tenant solutions is security assurance [See a related blog post by Ted Schadler of Forrester].