A cloud deployment model defines the nature of a public, hybrid and private cloud, especially with regard to where the physical infrastructure is deployed and who manages and maintains it.
Public clouds provide access to computing, storage, and additional resources for cloud consumers over the Internet but the resources themselves are owned by the organization selling the cloud services. The public cloud provider allows customers to self-provision resources typically via a web service interface but can also be provisioned through a command line interface (CLI). Customer's rent access to resources as needed on a pay-as-you-go basis. Public clouds offer access to large pools of scalable resources on a temporary basis without the need for capital investment in data center infrastructure.
Unlike a private cloud, infrastructure costs are shared across customers, which result in economies of scale. Data control might be an issue depending on a number of factors, including the type and sensitivity of the data as well as the industry and local laws concerning the data. In certain cases, use of a hybrid or private cloud may be required.
Private clouds give users immediate access to computing and storage resources hosted within an organization's infrastructure and behind the organization's firewall. The cloud resources are dedicated solely for that organization's use. Users self-provision and scale collections of resources drawn from the private cloud, typically via web service interface or command line interface, just as with a public cloud. However, because a private cloud is deployed within the organization's existing data center—and behind the organization's firewall—a private cloud is subject to the organization's physical, electronic, and procedural security measures and thus offers a higher degree of security and control over sensitive code and data.
With private cloud, the performance and tuning of physical hardware can be controlled and maintained by the organization, and can thus markedly improve server utilization and data center efficiency while reducing operational expense.
Hybrid clouds combine one or more public clouds and one or more private clouds by technology that enables data and application migration between them. Hybrid clouds typically use a shared API to enable hybrid operation. Note that hybrid cloud usage is in its infancy and that most organizations either start with the public cloud for Infrastructure as a Service or start with a private cloud if they've already invested in on-premise infrastructure and hardware.
With hybrid cloud, organizations can utilize the cost benefits of a public cloud and when needed, protect confidential data in a private cloud.
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