Public, private and hybrid clouds: differences explained

Although the concept of cloud computing has been around for decades, there is a new found frenzy among companies to go the ‘cloud route’ for as many of their enterprise business applications as possible. In its original form, cloud computing represents shared usage of computing resources; a concept that has been around from the age of the mainframe computer.


Cloud computing differs from traditional shared resource usage in that it represents the coming together of two important aspects, one which is technological, and the other which is business-related:

  • Virtualization: Almost all cloud computing platforms rely on some form of virtualization to create logically distinct resources based on user needs
  • Operational model: All cloud computing platforms rely on the ‘pay-as-you-use’ model, where traditional ‘capital expenditure’ in infrastructure, many a time an upfront investment, is transformed into ‘operational expenditure’. Nothing could be more attractive to an industry that was looking at cutting costs in every possible way!

What are the broad paradigms which the cloud computing paradigm has given birth to?

Public cloud

In its original form, a public cloud is formed when a provider, someone like Amazon, Google or a smaller company, makes computing resources, such as processing power, memory or storage, publicly available over the Internet. Another important aspect about public cloud infrastructure was that they typically run on open-source software. Public cloud, by definition, is hence a service where both hardware and applications are provided by the service provider, and costs are borne by users on a pay-as-you-use model.

The efficacy of public cloud services are measured by the extent of support to:

  • Creation of on demand virtual machine (VM) instances
  • Custom image support
  • Image library
  • Auto-scaling/provisioning
  • Storage provisioning

Private cloud

A private cloud represents a model where infrastructure is privately owned by an organization. Knowing that IT departments were nervous about using public clouds due to security reasons, these companies hit upon the term “private cloud” as a buzzword to describe a computing infrastructure privately held by a corporation that had capabilities similar to a cloud but was completely internal and thus more secure.

Hybrid cloud

The hybrid cloud is represents the best of both public and private clouds: if an organization has varying needs regarding computational resources and also has both sensitive and non-sensitive applications, it can use a hybrid cloud to get the best of both worlds. In most cases, the database servers, which generally contain sensitive information, are kept on a private cloud, and a public cloud is used for everything else. This solves the security problems of public clouds and lets an organization take advantage of all that public cloud has to offer when it comes to general computing resources.

For example, a company might use a public cloud service for email or workflow applications but keep financial and other sensitive data resources on its private cloud.

Industry research shows that the hybrid approach is catching on with many organizations. Forrester Research, in one of its recent reports said the most popular infrastructure-as-a-service (IaaS) strategy is a hybrid cloud strategy.

The firm surveyed 151 U.S. and European technology decision-makers whose organizations had already implemented IaaS, and 40 percent of them said they use IaaS as a complement to their on-premises server and storage resources for peak load or special demand. That compares with 20 percent who said they use IaaS for their entire server or compute resource and storage needs.

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