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Computerworld - As the hype over cloud computing evolves into a more substantive discussion, one thing has become clear -- customers do not want to be locked into a single cloud provider. They would like the freedom to move among the clouds -- ideally from public to private and back again. This would give customers the freedom to switch providers as their computing needs grow or shrink, and the ability to move applications and workloads around as their business requirements change.

But users and cloud vendors are in very different places on this issue, and true cloud interoperability will likely not occur for some time -- if ever. Standards are nascent and will take years to fully develop. Joe Skorupa, a Gartner vice president, says that even if an open cloud standard should come to pass, every provider would still continue to implement its own proprietary enhancements to differentiate its wares from the competition. Skorupa points out that vendors do not want clouds to become commodity products because they do not want to compete on price alone.

Bernard Golden, CEO of HyperStratus, a consulting firm in San Carlos, Calif. that specializes in virtualization and cloud computing, says it's unlikely that the industry will get to the point where there is some format that lets applications be "magically" moved to one or more different clouds. In part, he says, this situation is driven by the fact that "there is so much innovation going on in this space."

This lack of standards isn't stopping customers from moving to the cloud, although it is likely slowing them down. Jim Chilton, CIO - Americas for Dassault Systemes, which makes computer-assisted design and other software, says that his company's strategy has been to demonstrate that the migration of internal applications to public clouds is possible. He set up two proof-of-concept scenarios, one for disaster recovery and one for technical support, and selected CloudSwitch to migrate the applications due to its security and ease of use. The initial testing was successful and was managed by an internal IT team working with CloudSwitch.

Chilton has learned that it takes a little longer to do the migrations than expected, primarily because he was migrating physical applications to the Amazon EC2 cloud and needed to convert the applications to a virtualized version before they could be moved to the cloud. Chilton says, "The viability of migrating an application to a target cloud has to do with the maturity of the application," he says, and "legacy applications are a struggle to get virtualized, never mind migrating to a cloud." Virtualization is a first step toward moving applications to the cloud, most observers agree.

Chilton's experience is that legacy applications don't always work well or consistently when virtualized, and this adds to the complexity of migrating. His strategy in choosing what to migrate is to pick applications that are not critical on a day-to-day basis, as a way to validate the cloud model and gain internal buy-in.

Defining cloud interoperability -- and why getting there is so difficult

Like the word "cloud" itself, interoperability can mean different things to different people. One can mean the ability of applications to move from one environment to the next -- from Savvis to Amazon, for instance, and for the applications to work exactly the same in both places. Another might mean applications running in different clouds being able to share information, which might require having a common set of interfaces.

To others, such as James Urquhart, a market strategist at Cisco, cloud interoperability refers to the ability of customers to use the same management tools, server images and other software with a variety of cloud computing providers and platforms.

The essence of the problem, though, is that each vendor's cloud environment supports one or more operating systems and databases. Each cloud contains hypervisors, processes, security, a storage model, a networking model, a cloud API, licensing models and more. Rarely, if ever, do two providers implement their clouds in exactly the same way, with all the same moving pieces.

Kamesh Pemmaraju, cloud computing consultant at Sand Hill Group, says that, like in the traditional software and hardware worlds, interoperability in the cloud will first occur at the lower layers of the stack. At the infrastructure layer there is OVF (Open Virtualization Format), and of course there are standards for XML, HTML and various other protocols.

As you move up the cloud stack, he says, the lock-in gets stronger and stronger.