A cloud deployment model (different from a cloud service model) defines where the physical servers are deployed and hosted and who is responsible for managing and maintaining them.
Public clouds offer access to compute, storage, and network resources (and sometimes with additional platform features) for the general public over the Internet, but the physical cloud resources themselves are owned by the service provider that sells the cloud services. The public cloud provider allows customers to self-provision resources, typically via a web service interface. Customers rent access to public cloud resources as needed on a pay-as-you-go basis, usually billable by the hour. Public clouds offer access to large pools of elastic, highly scalable resources on a temporary or as-needed basis without the need for capital investment in data center infrastructure.
With a public cloud, infrastructure costs are shared across all customers, which results in economies of scale. Data control in a public cloud 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 data privacy and security. In addition, like any pay-as-you-go model, the more you use the public cloud resources, the more you will pay to the service provider over time. This is acceptable to many companies who have heavily fluctuating workloads, but for organizations that have reached a steady state of demand for an application, it may be worthwhile to do the cost analysis to see whether continuing to pay for the public cloud resources makes sense over investing in a private cloud infrastructure.
Private clouds give users immediate access to computing resources hosted within an organization's infrastructure and the 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, just as with a public cloud. However, because it 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 over sensitive code and data.
With private cloud, the performance of physical hardware can be controlled and maintained by the organization, and can thus markedly improve 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.
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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