Running Xen

David Martinjak writes "Running Xen: A Hands-On Guide to the Art of Virtualization was published by Prentice Hall, and authored by Jeanna N. Matthews, Eli M. Dow, Todd Deshane, Wenjin Hu, Jeremy Bongio, Patrick F. Wilbur, and Brendan Johnson. The book, which will be referred to as simply Running Xen, was a great resource on Xen and virtualization from the administration side. A wide range of topics was covered from installing Xen all the way up to managing virtual resources, including migrating guest environments. Overall, the explanations were concise and understandable; while the information was presented in a straightforward manner. Running Xen was definitely a useful resource for administering systems with Xen." Keep reading for the rest of David's review. Running Xen: A Hands-On Guide to the Art of Virtualization author Jeanna N. Matthews, Eli M. Dow, Todd Deshane, Wenjin Hu, Jeremy Bongio, Patrick F. Wilbur, and Brendan Johnson pages 586 publisher Prentice Hall rating 9 reviewer David Martinjak ISBN 0132349663 summary A hands-on guide to virtualization with Xen The flow of the book was intuitive, and reasonable; this was especially valuable for discussing a newer technology where the terms could be confusing. Fortunately, the authors kept the language clear so that the reader easily could understand the subject of discussion. This unambiguous presentation of content was a welcomed feature.

Running Xen started with a thorough-enough explanation of virtualization. Several different approaches to virtualization were compared and contrasted, which should help the reader to understand where Xen resides in the whole domain. This first chapter was a great introduction as it provided just the right amount of information. At no point did I consider the explanations to be short or lacking; nor did I feel overloaded with details. The authors seemed adequately aware that the title of the book was Running Xen, and they stuck to that scope.

After the introduction, the book moved right into actually running Xen. This helped to keep the my attention on the subject, and tied back in to the proper flow of the material. At first, the chapter began with baby steps. It introduced the Xen LiveCD, and information on working within the Xen environment. Subsequent chapters moved into a more intermediate level of usage: installing Xen in a third-party distrobution, and running pre-built guest images. Popular third-party distrobutions such as Ubuntu, Gentoo, CentOS, and OpenSUSE were covered; and this section also included instructions for using compiled Xen binaries and building your own from source.

One of the topics I was most interested in was building a custom, minimal guest environment from a particular distro. Chapter 7, "Populating Guest Images", provided all of the information I was looking for along with some other interesting facts. The popular distros were covered again (Ubuntu, Gentoo, etc.), but this time a twist was added to the mix. "Populating Guest Images" started off with installing Windows XP in Xen. This was a complete surprise to me. If you prefer GNU/Linux on the server, but Windows XP on the desktop, and have been looking to consolidate with virtualization; this chapter is a must-read. The chapter also helped solidify the understanding of concepts presented earlier in the book. For example, the first chapter discussed two different types of guests: paravirtual (PV) and Hardware Virtual Machine (HVM). In "Populating Guest Images", the authors led the reader through building guests of each type. The process was presented in a logical fashion which was easy to follow, making the book that much more enjoyable.

Running Xen then moved on to putting the guests on the network. Chapter 10, "Network Configuration", covered several options for networking guest environments in Xen. It would be an understatement to say that this chapter was thorough. Overall, the authors did a great job explaining the differences between the networking options, and how to implement each one. Unfortunately the needs of the reader are variable, so this chapter overflowed with information. The upside was that readers with complex virtualized network segments will not be disappointed. The downside was that I, personally, only really needed a small percentage of the chapter's content. Therefore, much of the chapter was technically irrelevant to me individually.

There was one other unfortunate issue, which occurred in the next chapter. Chapter 11, "Securing a Xen System", contained syntax errors for iptables rules. Mainly one dash was used instead of two when specifying the destination port in some rules. For example, LISTING 11.10 displayed the syntax -dport which caused an error. However, the syntax was correct at other places in the book (LISTING 10.24, for example). Additionally, there was a problem on output formatting where the command prompt and output lines ran together in the print (LISTING 11.11). This could cause confusion for some readers intently following the text.

My only complaint with the book was that the chapter on network configuration seemed to be rather long. For a person working with Xen at a business level, especially mid-size to enterprise, this chapter provided an excellent amount of insight and information. But for the person at home building his/her own test server for simple purposes, much of the content in this chapter was overkill. Additionally the few syntax errors were eye-sores, but any person with iptables experience could easily identify and fix the problems. It is just in my opinion, a published book should be syntactically correct so that the reader is not presented with contradicting results; nor should the reader have to conduct additional searches to rectify mistakes from the book's pages. However, these items are minor and pale in comparison to the outstanding wealth of knowledge in the text.

This book is highly recommended for anyone interested in virtualization with Xen. In addition to the regular paperback, Running Xen is also available on Safari. The paperback additionally includes a coupon code for a 45-day pass to access the book via Safari online.

David Martinjak is a programmer, GNU/Linux addict, and the director of 2600 in Cincinnati, Ohio. He can be reached at david.martinjak@gmail.com.

You can purchase Running Xen: A Hands-On Guide to the Art of Virtualization from amazon.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.

Comments

Nope. No one has heard of that book.

[spun]

On the other hand, most of us have read Zen and the Art of Motorcycle Maintenance. Which still doesn't tell you how to fix your motorcycle, that's what's so Zen about it.

"What's the sound of one hand adjusting a timing belt?"

Re:Does XEN have a future?

[squiggleslash]

Xen and KVM are completely different types of virtualization solution. The supposed rivalry between the two is largely bad journalism, not rooted in anything to do with the platforms themselves.

If you want to run a single physical computer with multiple operating system instances, such as replacing a bank of servers with a single machine, Xen is your guy. If you want to run VMs under Linux, KVM is your friend. Conflating the two is like comparing... well, to use a car analogy, for this is Slashdot, a railroad with a tractor trailer.

Re:Does XEN have a future?

[TheRaven64]

You're implying that Xen can't run VMs under Linux but KVM can, or Xen can run VMs on systems other than Linux or something that KVM can't do? They're both Linux only at this point, and Xen effectively runs a forked version of Linux because it isn't, and won't be, upstream. Xen is a hypervisor. It runs under Linux, not on top (although the Xen devs do often run Xen in KVM for development). It uses one or more slightly (or very, depending on your hardware) privileged guests to provide drivers. These can be Linux, NetBSD or Solaris.

KVM only works on systems that support hardware virtualisation. Xen will run unmodified operating systems on these platforms, but also supports paravirtualised guests on older systems (and paravirtualised guests are faster on any hardware). As far as I know, KVM is x86-only, while Xen runs on x86, PowerPC, Itanium and ARM (Samsung are doing some very cool things with Xen on ARM).

There are a few things that Xen supports that KVM doesn't, such as live migration. This is probably the right time for the obligatory plug for my book, if you want to learn more about how Xen works.

Re:Does XEN have a future?

[squiggleslash]

Well yes they do do things differently, but KVM does it better and simpler by just running on Linux as the base system hypervisor. From a maintenance point of view things get far simpler, as the OP said.

Sure, and Wifi does it better and simpler than Bluetooth by using Ethernet frames (The Bluetooth vs Wifi "war" is also a good example of where geeks get it completely, 100%, wrong by not recognizing the entirely different applications the technologies are aimed at.) You're comparing apples to oranges, and assuming that because KVM works better in a specific scenario that it works better.

That statement is just, well, daft. You're implying that Xen can't run VMs under Linux but KVM can, or Xen can run VMs on systems other than Linux or something that KVM can't do? They're both Linux only at this point, and Xen effectively runs a forked version of Linux because it isn't, and won't be, upstream

It's not daft, your response makes no sense. Let's break it down:

You're implying that Xen can't run VMs under Linux but KVM can

That's right. Xen cannot run VMs under Linux. Xen runs VMs on the bare hardware. In the Xen environment, operating systems run under Xen, not vice versa. The only way to run Xen "under" Linux is to run it in an emulator!

or Xen can run VMs on systems other than Linux or something that KVM can't do?

This sentence makes no sense as is. It can't run VMs under Linux, as stated above. In terms of operating system support, you can run various operating systems under Xen as "dom0". Dom0 is a special domain that most hardware is managed by by default (though you can redirect any almost piece of hardware to be managed by any guest system. For example, on my home server, one of the Ethernet cards is managed completely by a domU.) Dom0 can be one of many operating systems, including Linux-based systems, OpenSolaris/SunOS, OpenBSD, NetBSD, and certain versions of FreeBSD (with certain versions of Xen.) The only restrictions that go with being dom0 have to do with the kernels for those systems being Xen-aware.

This flexibility brings enormous advantages incidentally. With enough memory, you can install something like Solaris as your domU and have it export NFS shares upon a ZFS file system to all of the domUs, giving every operating system you run the advantages of the host. At the other extreme, you can install something small and light - bugs aside, I found Xen's integration with Ubuntu Server 8.04 LTS wonderful when setting up my little firewall-gateway/servers box. I have the barest Ubuntu Server installation (no X11/GNOME/etc) as dom0, and even barer systems for the domUs It's great.

They're both Linux only at this point, and Xen effectively runs a forked version of Linux because it isn't, and won't be, upstream.

Xen is PowerPC, ix86, and AMD64 at the moment. In terms of operating systems it can run as dom0, see above. In terms of operating systems it can run as domU, well, the choice is massive.

Really, what you're saying convinces me you haven't really investigated what makes Xen Xen. I would never install Xen on my laptop. I'd never install KVM on my server machine. Take another look at both, and see why their strengths make them suitable for different purposes, neither are solutions that fit every application, and they complement each other well in terms of the applications they efficiently support.