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
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.
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
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.