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The Xen vs. KVM debate was a staple in the open source virtualization space for years, but the conversation has mostly come to an end.
Back in 2014, many people were talking about whether to use Xen or KVM for virtualization. However, as of early 2019, it looks as if the battle is over and everybody is using KVM. So does that mean that Xen is dead or is there still some activity for the project?
Use cases for Xen
Let's begin with the good news for Xen Project fans: Xen is still alive. It's a project under the Linux Foundation, and new releases are still being published. For example, in collaboration with the Automotive Grade Linux project, the Xen Project recently demonstrated its digital cockpit, which can host different applications in a car based on Xen VMs.
Using Xen VMs to run these applications makes it easier to create strict separation between components that are important for safety -- such as the speedometer and odometer -- and applications that aren't, such as the multimedia and navigation system. Running different systems in VMs makes it possible to run the applications using just one computer instead of two. The reason Automotive Grade Linux uses Xen is that it supports different peripheral device virtualization methods, which offer better compliance with the safety requirements of these peripherals.
Xen vs. KVM in 2019
Even if Xen is still alive, it's undeniable that it has lost serious ground. AWS used to be one of the biggest Xen users, but the company announced in November 2017 that it would develop a new hypervisor based on KVM. With Amazon moving away from Xen, the Xen open source project seriously suffered, but it hasn't completely disappeared.
Looking at activity in the Xen code, it's obvious that active development still occurs, even if it's just by a handful of developers. That's because Amazon wasn't the last big player with a commercial interest in Xen. Citrix still offers its Citrix Hypervisor -- formerly known as Citrix XenServer -- a product based on open source Xen code. As long as Citrix stays involved, Xen technology shouldn't fall by the wayside.
KVM is the default
The situation for the KVM hypervisor is completely different, though. KVM is included in the Linux kernel, which makes the use cases for KVM so much clearer. All of the big Linux distributions offer it as their default platform, and it's used by major public clouds, such as the Google Cloud Platform and AWS.
The interesting thing about KVM is that it's a commodity, but not much news is published about it. This is probably due to the fact that KVM is integrated in the Linux kernel. KVM was also never a rich environment, as is the case with Xen, which started as a completely independent kernel.
In KVM, the ecosystem comes from the surrounding projects. These include QEMU tools, which provide user space utilities, and the oVirt interface, which provides a web interface that offers easy VM management.
So, to answer the question "What happened with the battle between KVM and Xen in 2019?" KVM won. Xen hasn't completely disappeared, and it still has some strong use cases, but it will never become the standard hypervisor for Linux or cloud.