What tools do Google, Amazon or Microsoft use? They are running millions of VMs, Presumably its proprietary?
Amazon uses Xen which they call "Xen 2" I think because they've made tons of improvements and optimizations over the years. Google uses kvm. They probably contribute as well although I haven't checked. From a quick search Azure uses a private build of hyper-v which surprises me actually but it's possible. Edit : millions of VMs doesn't mean anything, at the end of the day it's just servers each running a bunch of VM,…
Regarding AWS, I would also add Firecracker for AWS Lambda, which uses KVM.