Tag Archives: xen

Does AWS use Xen Hypervisor?

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.

What is the Xen Project?

Xen Project is open source baremetal hypervisor, integral part of the Linux kernel and available in Linux systems. It is one of the numerous projects that are handled by Linux Foundation.

Components of Xen Project

            Standard Xen-running environment is consisted of few different parts. There is a Domain 0, which is the way in which you call the operating system of the host. However, it is not a typical host OS because other virtual machines are not required to use it in order to gain access to the hardware of the host server. The so-called Domain 0 is only responsible for drivers` access, and if there is a need for some type of coordination then that will be properly handled by this Domain 0. Besides Domain 0, there are other virtual machines that are called Domain U.

            The Xen Project hypervisor can run many different operating systems on a single host or a machine. It is the one and only type 1 hypervisor that can be used as open source. Xen Project is typically used as a base for many different open source and commercial applications like desktop virtualization, server visualization, embedded Infrastructure as a Service, security applications and hardware appliances. A thing worth knowing is that Xen Project powers the biggest clouds you can find in production today.

            The main features of the Xen Project hypervisor are the following:

  • Paravirtualization is one key component through which the optimization is used so the paravirtualized guests run as virtual machines. That enables them to run faster in comparison to running wits some hardware extensions. Besides that, Xen Project hypervisor can run even on hardware that is not supportive of virtualization extensions.
  • Driver Isolation is another main feature. The hypervisor allows the driver of the main device to run inside the virtual machine. In case the driver is compromised or crashes, then the virtual machine that has the driver can be restarted and the driver will reboot without affecting or having any influence on other parts of the system.
  • The hypervisor has small interface and footprint, which is less than one megabyte in size. This is because it uses microkernel design and that leaves tiny memory footprint. That makes it more secure and more robust in comparison to other hypervisors.
  • Finally, operating system agnostic is another top feature. Many installations use Linux as their domain 0, but here many other operating systems can be used, such as OpenSolaris and NetBSD.