At the core of cloud computing discussions and cloud computing in general is the idea of virtualization. The word 'virtualization' might invoke different things depending on who you talk to but for cloud discussions many people think of virtual images: entire systems being stored even down to the operating systems. The advantages seem evident. Instead of complex deployment models you simply need to take an unused piece of hardware resource and lay in the exact pattern. The assumption is that the hardware is free an compatible but everything else is negotiable. I think, however that there are different levels of assumption within the cloud concept.
Laying in entire systems from the OS up may be way more work than is necessary. The advantage is that there are fewer constraints on what kinds of things you can depoy in your cloud. But one of the big disadvantages are that there are fewer constraints on what kinds of things you can depoy in your cloud. Sometimes, productivity is higher when your developers are given the topology parameters and when he knows what resources are going to be available.
In fact, the concept of cloud seems to infer that there are fewer assumptions needed so you will have maximum versatility. However, flexibility is an antagonist to stability and stability is needed for prodcutivity. In effect, more assumptions necessarily equals faster developement and quicker time to release. So is cloud the antithesis of productivity? No, of course not. The beauty of clouds is that you can have as many assumptions as you want.
A productive cloud model could assume specific hardware, OS and even webservers and macro-topologies. The cloud's resources could simply be avalable platforms that serve as quickly added nodes that can be dynamically provisioned within an appserver deployment.
I think cloud models can be stratfied based on the number of assumptions that are built into it. Level 0 clouds could be where the only assumtion is the that the physical machines will support the virtual images. Level 6 could be that virtual servers and resources can be cloned by template to act as expansion nodes to meet growing demand. Does this cross over into other scaling models? Yes. So what? It doesn't have to be unique in every aspect it merely has to be consistent for effective use.
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