During all the fuss of Citrix Synergy last week, an event of pretty earth-shattering importance occurred in the open source world: all key Xen code was accepted into the Linux mainline kernel. This brings to an elegant close an enormous effort on the part of the xen.org and Linux communities, including very substantial contributions from Oracle, Citrix and other key Xen proponents, and continued feedback and guidance from the Linux kernel maintainers. The specifics are superbly articulated by Wim Coekaerts of Oracle, who graciously acknowledges the community effort to get this done.
In practical terms, this means that every Linux kernel from 2.6.39 onwards, will contain every piece of code to seamlessly take the role of guest, host (in the case of KVM) or Domain 0 (in the case of Xen). For the key consumers of Xen, including open source powered clouds such as AWS, this achievement permits easy adoption of the latest and greatest Linux kernels, their drivers and other key architectural innovations, both to power the virtual infrastructure and as guest VMs. Whereas historically this required real engineering and code, this is no longer the case – it just runs.
So now you can use KVM as a component of your Linux distro, or you can use your Linux distro to run Dom0 (platform services) for Xen. This decoupling is unique to Linux, and to my mind gives Linux and the open source community the ability to support a far richer set of virtualized infrastructure abstractions.
I hope now that I will never again have to answer the “KVM vs Xen” question from analysts or customers. Pick your preferred way to consume virtualization – as an infrastructure abstraction independent of any OS (Xen), or as a component of your Linux distro (KVM). I’m a passionate advocate of the former – and I believe that customers have voted hands down for virtual infrastructure as a capability separated from any OS. But if you want to use a Linux based hypervisor, then KVM is a great technology and the right choice. Ultimately the Linux and Xen communities have done the right thing for developers, customers and the market in general, permitting choice. Kudos to all, and thanks to our fabulous community for its hard work.