News Stay informed about the latest enterprise technology news and product updates.

AWS using KVM and Xen, but users may not feel any impact

AWS has added a new hypervisor behind the scenes, but customers likely won’t see much of a direct impact on their cloud environment.

Amazon this month began selling its C5 instance nearly a year after first announcing the compute-heavy VMs would be built with the latest Intel chips. Tucked into a blog post about the C5’s general availability was mention of a new unspecified hypervisor to better coordinate with Amazon’s hardware. The company has since confirmed to SearchAWS that it is “KVM based.” Word of a possible switch to KVM was first reported by The Register, which cited a since-deleted FAQ from Amazon that said the hypervisor was KVM based.

AWS isn’t abandoning Xen, its hypervisor of choice since the outset of the platform. Instead, it will adopt a multi-hypervisor strategy with both Xen and KVM depending on a given workload’s specific requirements. We asked AWS if the introduction of KVM had to do with any issues with Xen; an AWS spokesperson responded with a statement that the P3 instances on sale since October use Xen, and the company will continue to heavily invest in Xen.

“For future platforms, we will use the best virtualization technology for each specific platform and plan to continue to launch platforms that are built on both Xen and our new hypervisor going forward,” the spokesperson said.

The addition of KVM addition is an interesting behind the scenes glimpse from a company that rarely discloses much about its internal architecture, but it’s unclear what if any impact customers will feel from this. In AWS’ shared-responsibility model, the hypervisor essentially acts as the line in the sand, with the virtualization, operating systems and physical hardware all the responsibility of the cloud provider.

Why would AWS go to the trouble to juggle different hypervisors for different instance types? AWS is believed to be the only major service provider working at scale that uses Xen, so part of the rational for the switch may be to save support and development costs by allowing KVM’s far larger community support to bear the brunt of that work.

“Amazon is notorious for taking open source and leveraging it for their own benefit and not giving back to the open source community,” said Keith Townsend, a TechTarget contributor and principal of The CTO Advisor LLC and founder of

And after a decade-plus of using Xen, AWS probably would be challenged to move everything to KVM, he said.

Such a hardware virtual machine (HVM) approach means a limited number of HVMs per node and a need for more hardware to handle larger nodes, said Edward L. Haletky, president of AstroArch Consulting in Austin, Texas. It also means AWS’ cloud management tools must go in a new direction and become multi-hypervisor. A bigger question is why Amazon isn’t simply calling the new hypervisor KVM.

“[It] means to me that they have modified it in some unknown way to either help it scale, access existing storage, security and networks, or some other set of elements within KVM,” he said.

The new hypervisor may well fit “hand-in-glove” with AWS hardware to optimize security and performance, as AWS chief evangelist Jeff Barr wrote in the blog post about the C5 instance. But customers likely won’t notice much of a difference.

“It’s more probable that it will impact [AWS’] bottom line but doesn’t necessarily impact the customer,” Townsend said.

Trevor Jones is a senior news writer with SearchCloudComputing and SearchAWS. Contact him at [email protected].

App Architecture
Cloud Computing
Software Quality