The appeal of making your own data center cloudlike is easy to understand: Who wouldn't want an entirely flexible commodity infrastructure, where you can pour on compute, storage, and network resources as needed?
From the early days of the cloud, CIOs saw promise in the cloud's magic combination of reduced cost and vastly greater agility and wanted to capitalize on cloud architecture in their own organizations. But those closer to the ground in enterprise IT have always had a tendency to roll their eyes. They see the advantage of scale-out, self-service architectures for some applications -- such as dev and test -- but the return on investment in other areas is not always so obvious.
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Part of that resistance is the usual allergic reaction to change, because major shakeups mean fewer resources to meet project deadlines and keep legacy systems humming. But there are also very good reasons why the private cloud is taking so long to take hold. The two leading ones are the immaturity and expense of available private cloud solutions.
Private IaaS shuffles along
The three major IaaS solutions remain the OpenStack framework-- a growing collection of open source projects revised twice a year -- and commercial IaaS solutions from Microsoft and VMware.
The word from the latest OpenStack conference is that adoption appears to have slowed, in part because OpenStack remains a moving target. To deploy OpenStack, customers generally need packaged versions -- from the likes of HP, Rackspace, RedHat, or Ubuntu -- or major professional services assistance. Both are often required by those serious about deploying OpenStack, and in the process, customers run a serious risk of being locked into the specific implementation they've adopted.
Microsoft has an interesting DIY hybrid cloud solution, where Windows Server and System Center together provide both private cloud infrastructure and a bridge to the Azure public cloud, but it's still evolving. With its vCloud Suite, VMware provides the most mature private cloud solution, but it's expensive enough to make you think twice about scaling it out.
From what I've heard, for the most part, private IaaS is still mainly used for dev and test -- so developers can access self-service features to reconfigure their environments (or at least have ops do that more easily). Interestingly, if you add deployment, this is also what PaaS (platform as a service) was designed to do.
Private PaaS seeks momentum
Although most people think of PaaS in terms of such public cloud offerings as Amazon Elastic Beanstock or Heroku, I actually think private PaaS offers the most compelling value proposition for the private cloud.
Private PaaS provides a modern replacement for the application server. You develop, test, and deploy applications that scale out on commodity servers rather than scale up on premium hardware; also, you can accommodate multiple languages and (theoretically) wrap governance around application development across your organization. A scale-out platform that can embrace almost all applications you develop in-house provides the most compelling reason I can think of for building your own cloud.