Note that I said compute there. Indeed the cloud has many other components, but infrastructure guys like me will mainly be concerned with compute. And maybe storage. And of course what connects things to either of those 2. Hmmm. OK, maybe it's more than just compute, but for all intents and purposes I'm going to try and stay focused on compute.
So lets talk about apps. See what I did there? At the end of the day, compute is only good for one thing - running apps. But I can't see us getting to this fluffy land of external federated clouds without a fundamental change to how most applications in an enterprise environment run. Now don't get me wrong - the whole point of cloud compute from infrastructure up is that we don't have to change the apps. I get that. But in reality, they're going to have to change - they have to become portable, and any state needs to move out of the endpoint and into somewhere central. Why? Because it's gonna be a looooong time before _data_ is held in an external cloud, if ever IMHO. As Tim O'Reilly points out in his recent post Web 2.0 and Cloud Computing:
The prospect of "my" data disappearing or being unavailable is far more alarming than, for example, the disappearance of a service that merely hosts an aggregated view of data that is available elsewhere.And I think that's the key point that a lot of skeptics are missing. As an individual I hold exactly the stance that Tim describes, and all I really care about are some photos, videos, my resume and my password database. None of that stuff is required in order for me to live. What stance do you imagine companies are going to have, who's very existence depends upon data and the manipulation thereof?
Cloud compute means exactly as the name implies. COMPUTE. As in run up a compute engine (ie. an OS + App + State stack), throw some data at it, get some data back, job done. At no point did that data originate from, persist in (for any meaningful amount of time), or return to the external cloud. The security, availability and integrity of that data during transit and processing is by no means trivial, but compared to storing that data in the external cloud it is.
Which leads me in a roundabout way back to why apps need to change in order for internal compute clouds to reach their full potential and for external compute clouds to become really viable. Apps need to be delivered predictably and efficiently, that we may throw data at them. Whether that is achieved by virtualising them, streaming them, packaging them the traditional way, the choice is yours. But start thinking about it now, lest your clouds do nothing but rain on you.