In most cases, a public cloud service will charge more to host your infrastructure long term than it would cost you to purchase and maintain that infrastructure yourself. By the same token, though, you don't want to buy and babysit infrastructure you need only part of the time.
That's one of the main ideas behind the hybrid cloud: Build and operate a private cloud in your own data center and burst to a service that charges by the hour when you need it.
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But you should be able to do that seamlessly -- and you have to trust the provider. That's why I was struck by what VMware CEO Paul Maritz said in a recent interview with IDG Enterprise Chief Content Office John Gallant and me, when he talked about the 1,000 or so public cloud service providers that are running the VMware stack:
Within that community, what we've elected to do is to try and pick a very small subset of [providers] who are committed to have the same suite in their public clouds. So in particular that user interface is going to be common between the two. The way that you describe and secure and manage your workloads will look the same internally versus externally.
In other words, VMware has cultivated an elite group of providers that is offering VMware-based infrastructure as a service to customers. VMware has close to 80 percent market share for a reason (see the InfoWorld Test Center's recent virtualization shoot-out for details). So in the hybrid cloud model, it should be reasonably seamless for a customer that has standardized on VMware to burst to a public cloud provider that offers VMware infrastructure as a service and manage it all as a whole. When I asked Maritz whether this was the general idea, he responded: "That's exactly what we're trying to do."