A cloud deployment model defines the differences between hybrid cloud, public cloud, and private cloud computing, as well as where the actual infrastructure is deployed, what level of control and visibility you have into the infrastructure, and who manages the infrastructure.
Public Cloud Computing
Public clouds allow consumers leased access to compute and storage resources hosted by a service provider. Unlike private cloud computing, the resources that constitute that particular public cloud are owned by the provider selling the cloud services. The public cloud provider allows customers to gain access to computing resources without the need to purchase, configure, and provision physical hardware in a server room or data center. With a public cloud, users can self-provision resources via a web interface or console. Customers rent these resources as needed on a pay-as-you-go basis. Public clouds, such as AWS, Microsoft Azure, and Google Compute Engine, offer access to large pools of scalable resources on a temporary basis without the need for capital investment in data center infrastructure.
With public 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, private cloud computing may be required
Private Cloud Computing
Private cloud computing gives 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 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—private cloud computing 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. Where private clouds differ from public clouds are in the ability to scale out to meet extremely high workload demands; not many organizations have the budget or resources to invest in massive data centers like AWS, Microsoft, and Google have with their public clouds. But what the private cloud gives up in scalability, it provides with more visibility and control over the underlying infrastructure.
With private cloud computing, 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 Cloud Computing
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.