"...Tim seems to feel that they are aspects of the types, while I’m of the opinion that they instead define the type. For example, by Tim’s definition, one characteristic of Utility Computing style clouds is virtual machine instances, where my definitions rather centers on that.I love that distinction. First, for those struggling to see how Amazon/GoGrid/Flexiscale/etc. relates to Google/Microsoft/Salesforce.com/Intuit/etc., it delineates a very clear difference. If you are reserving servers on which to run applications, it is IaaS. If you are running your application free of care about which and how many resources are consumed, then it is PaaS. Easy.
Here’s how I typically break down cloud computing styles:
Description: A problematic term, perhaps, because a few of the vendors employ it towards different ends, but I use it because it’s descriptive. Rather than deploy to virtualized instances, developers building on this style cloud platform write instead to a fabric. The fabric’s role is to abstract the underlying physical and logical architecture from the developer, and - typically - to assume the burden of scaling.
Example: Google App Engine
Description: Instance style clouds are characterized by, well, instances. Unlike the fabric cloud, there is little to no abstraction present within instance based clouds: they generally recreate - virtually - a typical physical infrastructure composed of instances that include memory, processing cycles, and so on. The lack of abstraction can offer developers more control, but this control is typically offered at the cost of transparent scaling.
Example: Amazon EC2"
However, I am even more excited by a thought that occurred to me as I read the post. One of the things that this particular distinction points out is the likelihood that the buyers of each type would be different classes of enterprise IT professionals.
Its not black and white, but I would be willing to bet heavily that :
The preponderance of interest in IaaS is from those whose primary concern is system administration; those with complex application profiles, who want to tweak scalability themselves, and who want the freedom to determine how data and code get stored, accessed and acted upon.
The preponderance of interest in PaaS is from those whose primary concerns is application development; those with a functional orientation, who want to be more concerned about creating application experiences than worrying about how to architect for deployment in a web environment (or whatever the framework provides).
Now, the question quickly becomes, if developers can get the functionality and scalability/reliability/availability required from PaaS, without hiring the system administrators, why would any enterprise choose IaaS unless they were innovating at the architecture level? On the other hand, if all you want to do is add capacity to existing functionality, or you require an unusual or even innovative architecture, or you need to guarantee that certain security and continuity precautions are in place, why would you ever choose PaaS?
This, in turn, boils right back down to the PaaS spectrum I spoke of recently. Choose your cloud type based on your true need, but also take into account the skill set you will require. Don't focus on a single brand just because it's cool to your peers. Pick IaaS if you want to tweak infrastructure, otherwise by all means find the PaaS platform that best suits you. You'll probably save in the long run.
Now, I've clearly suppressed the fact that developers probably still want some portability...though I must note that choosing a programming language alone limits function portability. (Perhaps that's OK if the productivity values out weigh the likelihood of having to port.) Also, the things that system administrators are doing in the enterprise are extremely important, like managing security, data integrity and continuity. There are no guarantees that any of the existing PaaS platforms can help you with any of that.
Something to think about, anyway. What do you think? Will developers lean towards PaaS, while system administrators lean towards IaaS? Who will win the right to choose within the enterprise?