As enterprise interest in cloud computing offerings and concepts continues to increase, the number of solutions in both the public and private cloud spaces increases as well. There's been much debate over public versus private cloud, even to the point of debating whether there can be such a thing as a private cloud. I'm not here to debate the latter (in my opinion the location of the service has nothing to do with whether or not it is a cloud), but rather I want to take a look into why consumers would choose private clouds over their public counterparts.

During the last several months, Ive been lucky enough to chat with numerous enterprise users about their thoughts on cloud computing. Quite a few of these users are already utilizing the cloud on some level, and they are doing this by leveraging both public and private clouds. In my experience, enterprises have been more comfortable leveraging the private cloud initially and using that as a stepping stone to jump into the public realm when and where it makes sense.

For enterprise users that have chosen the private cloud approach, I always try to understand their reasoning behind such an approach. Over time, it has become pretty clear to me that there is a common set of requirements and reasons users choose a private cloud. Here are the top five most common reasons I hear for implementing private clouds:

1. Security and privacy: This is probably the most obvious and prevalent reason regardless of the argument that public clouds can be more secure than on-premise data centers. Perception is reality and sometimes users are very wary of putting their confidential data and applications in a cloud they dont necessarily control.
2. Customization: Users who require highly tailored, customized environments are likely to go the private cloud route simply because customizations are easier to achieve. Often times, public cloud solutions focus on offering the most common services. While good for a large majority of the users, that approach doesnt suit all needs.
3. Tight operational control: Some enterprise users desire complete control over the behavior of their cloud-based services. For instance, public cloud providers may not guarantee the necessary of level of performance for the network, infrastructure, and application services they provide.
4. Governance: In my observations, the perception of many public cloud offerings is that they sometimes lack in providing capabilities that enable proper governance. Users expect to be able to apply many of the same governance concepts in SOA to their use of cloud. In some cases, this desire is strong enough to shun public clouds in favor of implementing a governance model around their own private cloud.
5. Existing investment: In some situations it comes down to the very simple fact that a company has significant existing investment in their IT infrastructure. If a relatively inexpensive solution can be implemented to help them better leverage this infrastructure via a private cloud, they are more likely to embrace that than turn their back on the investment in favor of an entirely new approach via the public cloud.

I think there's definitely a time and place for both public and private clouds. In my opinion it is unwise to dismiss private clouds out of hand, and I think it equally unwise to think enterprises cannot make use of public clouds. I'd like to hear what you think too. If you are leveraging cloud services are they public or private and why did you choose that particular approach?