As you may have seen in my recent blog “4 reasons to move your applications to the cloud” I have embarked on an attempt to explain the world of cloud computing and why we should move our applications there sooner rather than later.

This is no mean feat but bear with me, I hope you will find these articles at least of some use to you in your decision making process. So having discussed the reasons to move to the cloud this article will try and outline each of the cloud models and their relative pros and cons. Cloud is a huge hype area so I have tried to stick to the main models but if I have missed anything significant do let me know.

As I see it there are four main types of cloud

  1.  Public Cloud 

Wikipedia defines the Public Cloud as a system where “resources are dynamically provisioned on a fine-grained, self-service basis over the Internet, via web applications/web services, from an off-site third-party provider who bills on a fine-grained utility computing basis” . This is the type of Cloud is probably the one we are all most familiar with and use every day from Hotmail to Google Docs to Flickr and comes with the benefits of being cheaper, greener, using cap ex spending rather than op ex etc etc. However this has also proved to be the most contentious as arguments rage over security levels.

  1.  Private Cloud

Defined as the “delivery of IaaS to a restricted set of customers, usually within a single organization” offers the ability to host applications or environments on infrastructure dedicated to a particular set of users, this provides the majority of the benefits of cloud computing (such as reduced costs) but the responsibility and the cost of the purchase and maintenance of the hardware remains with the end user. For this very reason many argue Private clouds are not really cloud computing at all. Eric Knorr notes “no early private cloud adopters (none that I’ve heard of, anyway) have made the quixotic attempt to turn their entire infrastructure into a private cloud. Instead, they have identified certain areas where the cloud model makes sense, such as development and test, a low-risk use case we’ve heard about for awhile.”

  1.  Community Cloud 

A community cloud is defined as “The cloud infrastructure is shared by several organizations and supports a specific community that has shared concerns (eg, mission, security requirements, policy, and compliance considerations). It may be managed by the organizations or a third party and may exist on premise or off premise.” A community cloud exists where several different companies share infrastructure, this allows them to unlock the majority of the benefits of cloud computing such as the economies of scale but with a higher level of security. Examples of community clouds include the G cloud which the UK government are currently working on launching.

  1.  Hybrid Cloud

Defined as “the cloud infrastructure is a composition of two or more clouds that remain unique entities but are bound together by standardized or proprietary technology that enables data and application portability” the Hybrid Cloud model is all about the ability to relay data and logic from core enterprise applications that reside on premise to other applications that reside in the cloud. The user does not know or care where that logic comes from, whether it’s from a private cloud or public cloud or the enterprise servers. This allows organisations to deploy applications and data where and when they want them—whether it’s private cloud, public cloud or on-premise.

Which option should you choose?

Of course every organisation is different with unique requirements however despite the wishful thinking and propaganda from some of the cloud vendor-giants, I believe that not all companies will be shifting their mission-critical business applications and databases off their own servers and into a vendor-hosted cloud offering tomorrow.

This means that by far, the larger proportion of enterprise applications will remain on-premise for a good few years to come and that the Hybrid Cloud will be the first port of call for the vast majority of us. Cloud computing is an essential strategic inflexion point that we must adopt if we are to remain on track with forward-looking computing methodologies.

Having discussed why one should move to the cloud and the different options available subsequent posts will show us how to make that big push to get there.