[1] http://www.vmware.com/products/datacenter-virtualization/vsp...
http://kb.vmware.com/selfservice/microsites/search.do?langua...
The original article just struck me as yet another company that doesn't know how to properly run applications in virtualized environments. Yes, if your hosting provider supports hot or cold migrations, you should be aware and develop accordingly. I do see this quite often, that still today, people are surprised that their VM is not always running on the same physical box at all times.
The problem they have is that they are trying to support arbitrary Python (which includes underlying libraries like LAPACK which depend on runtime CPU detection working correctly) and expecting code will work the same across identical instance types.
I think normal people would consider this a fair assumption, and in the event that AWS's advertised CPU capabilities were not broken for some instances, it would hold.
I don't think it's fair to say that they're ignorant of how virtualisation works. Disclaimer: I am a huge picloud fan and they have saved me a lot of time.
This has nothing to do with not running on the same physical box and more to do with some physical boxes are advertising incorrect instruction sets to the OS.
With that said, you can "migrate" EBS-backed instances by start/stopping them which (may) place them on different hardware Indeed, if you are large enough, you'll occasionally get emails from Amazon directing you to do just that due to scheduled maintenance on the physical machines.
The best part of that day was a guy from the government who gave a great talk on his experiences virtualising from running separate physical servers. While he was very much in favour of it, he mentioned a few drawbacks that the vendor talks obviously played down, but probably the best thing he said was "when doing something major with infrastructure like this, get your boss at the top on board early, because everyone above you will try to scuttle it to CYA if it goes wrong."