Private Cloud, Defined

Wednesday Jan 27th 2010 by Paul Rubens

'Private cloud' is a term heard often these days. What does it actually mean?

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"Private cloud" is a term heard a lot these days, but what does it actually mean?

Before trying to pin down this elusive beast, it's useful first to think about what's meant by cloud computing. Defining "cloud" is not easy, but a cloud computing solution will almost certainly offer:

  • Elasticity and scalability. This encompasses the idea of computing on demand, and the ability to increase the supply of computing resources as they are needed to deal with spikes in demand for a particular application or service. There's also the idea of turning computing resources into a commodity so more can be added over time, as needed, to ensure systems are almost infinitely scalable.
  • Pay as you go computing. This involves paying for the computing resources you use for the amount of time that you use them. In a private cloud, customers are generally be individual departments or business units.
  • Service level agreements. In many ways what drives the cloud computing model is the need for set performance levels. Elasticity, scalability and the pay-as-you-go model all follow from the need for an economical way to get set desired service levels at all times, even when demand spikes unpredictably.
  • Lower costs. A fundamental attraction of cloud computing is that it can provide an opportunity to reduce costs. Savings come from the use of computing resources based at one or more low-cost locations, which are managed efficiently using automation, and by realizing economies of scale stemming from the use of specialist staff members managing large quantities of computing resources
  • .

Although it's arguably not a requirement of cloud computing, the key technology enabler is virtualization. This allows a number of physical servers to be pooled into a large computing resource that can be used to run as many virtual machines of almost any size as are needed at any given time.

The Downside of Cloud Computing

The problem is that there are a number of objections to the cloud computing model. Common ones raised by many CIOs include a loss of control over enterprise and customer data, worries about security, and issues connected to regulatory compliance. Private clouds aim to avoid these objections, while still offering many of the key benefits of public cloud computing.

The obvious way around these objections is to implement something that looks like a cloud platform but sits safely within the corporate firewall, under the control of the IT department. This type of private cloud comes at a cost: The organization implementing the private cloud is still responsible for running and managing IT resources instead of being able to pass that responsibility on to a specialist third-party operator. Therefore there is less opportunity to enjoy the economies of scale that a large, highly automated cloud platform should offer. But must private clouds be like this? To answer this question, we must be clear about what we mean by "private" in this context.

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Private Cloud Complexities and Considerations

And that's actually rather tricky to define. A company server room containing a self-contained cloud infrastructure as described above would certainly count as a private cloud, but there are other things to take into account besides the physical location of the servers themselves. For example, if a similar infrastructure, controlled by an enterprise, is located in a third-party data center operator's facility, is that still a private cloud?

Things to consider include:

  • Who owns and manages the cloud platform itself?
  • Are other companies' virtual machines are hosted on the same cloud platform?
  • Who ends up being liable if SLAs are breached?
  • Who manages and controls the applications running on the cloud platform?
  • Could a third party be compelled and able to hand over data to law enforcement bodies?
  • Is the enterprise is connected to its cloud infrastructure over a private or public network?

If you think of a private cloud as something acceptable to companies that find running applications in a public cloud unacceptable, then perhaps the most helpful way to define a private cloud — even if it is not a technical definition — is this: It is simply a cloud solution that offers a significant proportion of the benefits of a public cloud, while addressing all the concerns that using a public cloud may raise. Depending on the organization in question, these concerns are likely to include physical location and ownership, application control, data security and liability for breaches of SLAs.

It's worth pointing out that some private cloud solutions have the capability to "cloud-burst" into a public cloud at peak times when additional resources are needed. The definition above almost certainly still holds for this type of system though, as most organizations will only cloud-burst less-important applications (in terms of data security, compliance and so on) to free up resources in their private clouds for more important or sensitive ones.

Despite this lack of a technical definition, there's no doubt that private clouds are more than just an idea: the likes of Arjuna, Elastra, Cassatt, Enomaly all have offerings that fall within this loose definition, and more are in the pipeline. Private clouds are here, and they are here now, even if no one knows exactly how to define them.

Paul Rubens is a journalist based in Marlow on Thames, England. He has been programming, tinkering and generally sitting in front of computer screens since his first encounter with a DEC PDP-11 in 1979.

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