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Xen @ Build a Cloud Day Boston

By December 22, 2011March 4th, 2019Uncategorized

As I mentioned in the Xen Day post, was offered a slot at the Build an Open Source Cloud Day Boston. The Build a Cloud attendees were great. They were very engaged and asked lots of questions. The questions gave me a chance to cover several Xen topics that I tend to take for granted. In this post I’ll outline the talk that I gave and highlight some of the questions that were asked and discuss the answers.
The slides for the talk are available here:
I decided to name the talk “Why Choose Xen For Your Cloud?” so that I could cover the history of Xen in the cloud, specific architectural advantages of Xen, and then cover XCP and Project Kronos. I don’t think that a lot of people realize that “Global Public Computing”  (or Cloud Computing as we know it today) was an idea that led to Xen. In other words, the Xen hypervisor was the solution to the need to break up, isolate, and provide accounting for system resources. Xen was born in the cloud. It’s no surprise then that Amazon EC2, Slicehost (now Rackspace Cloud Servers), and many others have chosen Xen as the basis of their clouds.
As I mentioned about Xen Dom0 support getting into the mainline Linux kernel, I got my first question (something like) “Isn’t Xen support in the Linux kernel going away due to KVM?”. To which I answered no, but let me clarify.  The question makes more sense for someone who is both a Linux expert and virtualization novice since the Linux kernel community is very strict about what it allows into the kernel. For instance, multiple implementations of the same functionality will not be accepted, but an abstracted version that can support more than one specific implementation is often required (OpenVZ is not in mainline, but Linux container components, often inspired by OpenVZ concepts, are included) . The main reason that Xen Dom0 support and KVM are both in the Linux kernel is that Xen and KVM have different architectures. Xen is a type-!, stand-alone hypervisor and KVM is a type-2, integrated hypervisor (I dig into these concepts again soon). Next to further clarify, Xen the hypervisor will never be included in Linux nor is it intended to be. When Xen was first created the Linux kernel at the time was used as a basis, but in a very special way (as explained by Keir Fraser) – the kernel was cut horizontally and the low level bits became the Xen hypervisor and the top part became the first Dom0. The Xen hypervisor is first to the hardware, followed by guest domains (including Dom0), by intentional design and is a fundamental requirement for being a type-1 hypervisor.
Next, as I covered the basic architectural design of a Xen system and its security benefits I was asked to clarify the difference between a type-1 and type-2 hypervisor. I find that the best way to explain this in a practical way that others can quickly understand is by using VMware ESX (the bare-metal, type-1 hypervisor from VMware) and VMware Workstation (the workstation class, install on top of an existing OS, type-2 hypervisor from VMware) since VMware is very well known and people can understand the difference. This question and answer are a perfect lead-in for the architectural and security advantages of Xen. In short, Xen has a small, well-defined, clean, and disaggregatable trusted computing base. This is in contrast to type-2 solutions, but also in contrast to type-1 hypervisors that put more services (perhaps than necessary or desired) into the hypervisor itself. Xen has unique security advantages primarily due to its well-architected design.
Since we were given an hour and fifteen minute slot, the XCP slides are fleshed out a bit more than I have presented in the past. Fortunately, our Xen Day team had prepared some really great materials and I was able to easily leverage those materials and re-focus them for the Build A Cloud/USENIX LISA audience. In particular, it is important to note the XAPI class diagram and cover the basic structure in some detail. The idea being that it helps system admins become familiar with the terminology they will need to master the xe command, but also that these devops-minded admins will likely be interested in writing scripts/tools that make direct XAPI calls. XAPI is great API for the cloud.

The rest of the XCP discussion is centered around why XCP is a great cloud platform. One of the key concepts that XCP, Open vSwitch, and the management tools address is mult-tenancy (multiple independent entities that need to share the same cloud and yet be isolated). XCP really shines for this cloud-minded audience and at least a few people were convinced to skip out on some of the Build a Cloud Day sessions and attend some of the Xen Day afternoon sessions to find out more about XCP. Xen Day took a deep dive into XCP.
XCP and cloud orchestration is an incredible story especially considering that XCP 1.0 was released in 2011. XCP is used in the first commercially available OpenStack cloud from Internap. CloudStack, which is a mature and feature-rich product itself, has also added support for XCP. OpenNebula also recently added support for XCP.  XCP is a great de-facto open source platform to build a cloud on.
I’ve spent a lot of time (and presented in more detail) presentations on Project Kronos, which in a very short time has been developed and is nearing a initial release. Stay tuned to the blog for updates on Project Kronos status. Current documentation on installing and using Project Kronos is available on the Xen wiki: