Admittedly, I've tended on this blog to cover the KVM hypervisor more often than Xen. For a long time, the former long seemed to have more momentum within the world of open source virtualization technology. Although younger than Xen, KVM has developed rapidly into a full-featured virtualization platform, and its integration into the Linux kernel makes it a more obvious choice in many circumstances than Xen.
Xen in Ubuntu 12.04 and BeyondYet even as KVM has matured and gained mindshare among the Linux server community, Xen has been holding its own, a fact made most evident recently by the announcement of support for the Xen Cloud Platform package and other key pieces of Xen software within the Ubuntu 12.04 "Universe" repository. This accomplishment comes thanks largely to the work of the Xen team's Project Kronos, which was launched five months ago with the goal of making it easier to integrate Xen into Debian and Ubuntu's package management systems.
Granted, the inclusion of Xen in the Ubuntu Universe repository comes up a bit short of "official" Xen endorsement by Canonical, which would mean including the packages in the "Main" repository (where the KVM package is housed). Universe is only for community supported projects.
Nonetheless, this update means it will be easier than ever for Ubuntu server administrators -- and even some desktop users, since there's nothing stopping them from experimenting with Xen as a virtualization platform as well, even though it may not be as user friendly for their needs as choices such as VirtualBox -- to install Xen and keep it updated.
And that's worth noting because it shows that KVM has not stolen the show yet. Xen remains a serious contender in the world of open source virtualization -- as it well should given its robust feature set, which includes highly advanced functionality such as paravirtualization and "live migration" of virtual machines. Xen also supports a range of operating systems as guests, including not only virtually every mainstream Linux- and Unix-like platform but also Windows, for which paravirtualized drivers are available to increase performance.
In addition, if the Xen developers are to be believed, we can look forward to more Xen-Ubuntu collaboration in the future. As they promise: "This is just the beginning: XCP in Ubuntu will evolve with the help of our user and developer communities. You can influence the direction of XCP in Ubuntu by attending the XCP design and Xen design session at Ubuntu Developer Summit – Q."