AWS stands for Amazon Web Services and the question whether AWS uses Xen supervisor intrigues many people. Truth is that AWS is changing its tune because the new hypervisor plan is the way to go in the future. At the moment AWS uses a customized version of the popular Xen hypervisor. It takes advantage of the feature called paravirtualization because the paravirtualized guests are strongly relying on the Xen hypervisor for support of actions that usually require privileged access. The CPU has four different privilege modes – between 0-3 are called rings. Ring 0 is the one with highest privilege which is executed by the host OS. However, instead of executing in Ring 0 like most OS do, the guest OS is running into Ring 1 and the other applications in the lowest Ring 3. This virtualization of the resources points to clear separation between the hypervisor and the guest, which results in added security between the two.
What Goes On At the Moment?
AWS has added brand new hypervisor, but truth is that customers will likely not notice huge impact when working in their cloud environment. The AWS now has KVM based hypervisor. It uses multi-hypervisor tactics by utilizing both Xen and KVM, depending on the specific requirements. AWS claim that they do not have any issues with Xen, they do continue to invest in it, but are seeking other options as well. All future platforms are expected to be used with best virtualization technology available. AWS plans to launch platforms which are built both on Xen and the KVM platform. The addition of KVM is interesting, but it is not very known whether this has any impact on the customers.
AWS is juggling between Xen and other hypervisors for different instance types, and they are the only big services provider that still use Xen. The reason why they are using KVM is to cut some costs for development and support. After using Xen over a decade, AWS is challenged to transfer everything to KVM, but they are still not completely abandoning Xen. They are still working on many details that need to be perfected first. The AWS tools for cloud management must go towards new direction and evolve into multi-hypervisor. The new hypervisor will likely fit well with AWS hardware and will provide optimized security features and performance, but the final consumers will likely not notice any big difference.