Cloud computing is an information technology revolution on par with the advent of the personal computer. Few technology fads claim to deliver so many benefits together with so much cost savings. And as the hype has grown, more and more vendors are rushing into the fray with their own "cloud" solutions. But not all clouds are created equal, and some clouds are not even really clouds at all. One of the debates that is starting to emerge in this area is "public cloud" vs. "private cloud". In this article, we will attempt to describe some of the key differences between public and private clouds, ultimately leading to the conclusion that private cloud is an oxymoron and there is only one type of cloud.
One of the reasons that the term "private cloud" has been gaining in popularity lately is that it has the appearance of offering all the benefits of the cloud and none of the security risks. This myth is very nicely dispelled in an article entitled "The Two Biggest Lies About Cloud Security" by Bernard Golden CEO of HyperStratus.
As we dig deeper into the differences between "private cloud" and "public cloud" we can conduct an examination of some key infrastructure and operational aspects:
Capital expenditure -- In a public cloud, the cloud provider is responsible for 100% of the capital expense. They procure, deploy and maintain all of the hardware, software and other infrastructure that is necessary for the customer. In a "private cloud", the customer is solely responsible for any and all capital expense associated with deploying an application or scaling to add users to an existing one.
Operational expenditure -- In a public cloud the operational expenses are shared by the provider and the customer. In a private cloud, the customer is responsible for 100% of the operational expenses. Furthermore, the multi-tenancy of the public cloud means that providers are able to offer services for significantly less than it would cost the customer to deliver those services on their own.
Availability -- public clouds are typically highly available with SLA's to back that up. For example Gmail achieved a 99.984% uptime in 2010 with no scheduled downtime whatsoever. Private clouds are typically much less reliable and have regularly scheduled down time for maintenance etc. While private clouds can be made more reliable, the cost of doing so grows exponentially.
Scalability -- public clouds are highly scalable and customers can add large numbers of users in a self service fashion. Private clouds are "chunky" in their scalability, often requiring additional chunks of infrastructure at certain user increments (e.g. every 500 or 1000 users.)
Mobile device access -- with tablets and smartphones rapidly rising in popularity it's important to point out that private clouds typically have poor support for mobile devices with the customer again responsible for necessary additions to enable mobile device access. Public clouds on the other hand, typically have excellent support for mobile devices as they only require a web browser in order to access the applications.
Standards -- Building on the last point, public clouds are often built on open standards such as HTML 5, JavaScript and CSS. Private clouds are built on closed, proprietary technologies that contribute to vendor lock in.
While the cloud hype does rage on, we hope that this article has helped to clarify some of the differences between "private clouds" and "public clouds" and has effectively demonstrated that private clouds do not offer all the benefits of cloud computing with little/none of the risks. Going one step further, we would suggest that the term private cloud is just an attempt by many traditional IT vendors to capitalize on the cloud movement and that the term "private cloud" is actually an oxymoron.
Adam Swidler is a Sr. Manager at Google Enterprise.
