Or when is a cloud not a cloud?
The economies afforded by using a public cloud arise from the utility pricing model where customers are charged only for the resources that they use. Maximum cost savings are made by minimising the resources that are consumed but with the benefit that, if additional resources are required, they are instantly available at a known cost. This is achievable for public cloud providers because a very large number of customers share a very large number of resources, each using a very small proportion. The cloud provider makes money through economies of scale as peaks average out and the amount of additional capacity required can be kept relatively small. Utilisation for a single customer is very low, but average utilisation for the cloud provider is relatively high.
Compare this with a customer employing a private cloud. The private cloud is a shared resource, but can only be shared by the subset of applications within the customer estate that are cloud-ready. Because the cloud is private, the entire cost of the cloud falls to the customer, regardless of whether they are using the resources or not. Applying a utility cost model to a private cloud doesn’t work (or is risky, at least) because somebody has to pay for the unused resources. So, in order to realise maximum cost benefit, utilisation of the private cloud must be as high as possible. But if utilisation is kept high, one of the major benefits of the cloud is lost; immediate elasticity. If the unthinkable happens (that the private cloud runs out of resource) the situation for customers is potentially worse than in a non-cloud environment as the lead time to procure and deploy additional nodes for a private cloud are potentially longer than procuring commodity servers. In order to mitigate the risk, there may be a tendency for service owners to want to ring-fence cloud resources, creating their own private cloud, and simply exacerbating the problem. Simply, the bigger the cloud, the more cost effective it is. As the size of a cloud reduces, it becomes nothing more than a standardised infrastructure platform offering a number of middleware services.
There are important differentiators between public and private clouds with advantages and disadvantages to each. Major candidates for private clouds include the public sector. But maybe greater benefit could be gained by promoting the use of a G-Cloud, an accredited cloud resource that is shared across the public sector but delivered by an accredited cloud service provider. I think I may know of such a service provider...
Sep 10 2010, 12:55 PM