» Public clouds are provided by a designated service provider for general public under a utility based pay-per-use consumption model. The cloud resources are hosted generally on the service provider’s premises. Popular examples of public clouds are Amazon’s AWS (EC2, S3 etc.), Rackspace Cloud Suite, and Microsoft’s Azure Service Platform.
» Private clouds are built, operated, and managed by an organization for its internal use only to support its business operations exclusively. Public, private, and government organizations worldwide are adopting this model to exploit the cloud benefits like flexibility, cost reduction, agility and so on.
» Virtual private clouds are a derivative of the private cloud deployment model but are further characterized by an isolated and secure segment of resources, created as an overlay on top of public cloud infrastructure using advanced network virtualization capabilities. Some of the public cloud vendors that offer this capability include Amazon Virtual Private Cloud, OpSource Cloud, and Skytap Virtual Lab.
» Community clouds are shared by several organizations and support a specific community that has shared concerns (e.g., mission, security requirements, policy, and compliance considerations). They may be managed by the organizations or a third party and may exist on premise or off premise. One example of this is OpenCirrus formed by HP, Intel, Yahoo, and others.
» Managed clouds arise when the physical infrastructure is owned by and/or physically located in the organization’s data centers with an extension of management and security control plane controlled by the managed service provider. This deployment model isn’t widely agreed upon, however, some vendors like ENKI and NaviSite’s NaviCloud offers claim to be managed cloud offerings.
» Hybrid clouds are a composition of two or more clouds (private, community, or public) that remain unique entities but are bound together by standardized or proprietary technology that enables data and application portability (e.g., cloud bursting for load-balancing between clouds). Recently some cloud vendors have started offering solutions which can be used to enable these hybrid cloud deployment models. Some examples of these offerings include Amazon Virtual Private Cloud, Skytap Virtual Lab, and CohesiveFT VPN-Cubed. These solutions work by
creating IPSec VPN tunneling capabilities to connect the public cloud infrastructure to the on-premise cloud resources.
The selection of a deployment model depends on the opportunities to increase earnings and reduce costs i.e. capital expenses (CAPEX) and operating expenses (OPEX). Such opportunities can also have an element of timeliness associated with it, in that decisions that lead to losses today could be done with a vision of increased earnings and cost reductions in a foreseeable future.
Source of Information : Wiley - Cloud Computing Principles and Paradigms