I’ve been looking at virtualization of OSs. No big surprise there… pretty normal stuff.

No. I’m not doing EC2. Hell, it’s not even about what it is I’m doing.

It’s widely known that the software that is used in the EC2 virtual machines is Xen. (Source: Wikipedia) I started looking at some of the spec pages for Xen and it just blew my mind.

One of the features is being able to move a VM from one physical host to another. While it’s running.

Holy crap.

You get a delay of 60-300ms at the end while the underlying hardware gets switched out from under the VM.

This, to me, is mind blowing.

I understand how this is done. I know roughly (ok, pretty specifically… copy-on-write memory pages and tracking clean vs. dirty pages) how this works. But actually implementing this in practice is another thing altogether.

I’m impressed.