Cloud computing uses a shared pool of computing resources (e.g., networks, servers, storage, applications, and services) to provide on-demand network access. Using virtualisation in data centre environments, Cloud computing can be rapidly scaled with minimal management and effort.
The National Institute of Standards and Technology (NIST) has defined four types of cloud deployment models:
A private cloud is created exclusively for a single organisation. The infrastructure could be physically located on or off site, and may be owned by a separate provider. The private cloud provides services only to members of the single organisation.
A public cloud is created for use by the general public. The infrastructure is physically located on the provider’s site, but may be owned by one or multiple organisations that could include businesses, academic institutions, or governments.
A community cloud is created for exclusive use by a specific community. The community consists of multiple organisations that have shared concerns (e.g., mission, security requirements, policy, and compliance considerations). The infrastructure could be physically located on or off site, and may be owned by a separate provider or by one or more of the organisations in the community. The differences between public clouds and community clouds are the functional needs that have been customised for the community. For example, healthcare organisations must remain compliant with policies and laws (e.g., HIPAA) that require special authentication and confidentiality. Organisations can share the implementation effort of these requirements across a common cloud deployment.
A hybrid cloud infrastructure is a composition of two or more distinct cloud infrastructures (private, community, or public) that are unique entities. These entities are bound together by technology that enables data and application portability. This portability allows an organisation to maintain a single perspective of a cloud solution while taking advantage of the strengths available from different cloud providers. For example, geography (location to end users), bandwidth, policy or law requirements, security, and cost are all features that may differentiate providers. A hybrid cloud offers the flexibility to adjust and react to these provider services, on demand.