Experiences with #Xen on #Linux : SUCKAGE ANALYSIS

[I would provide more links but I can’t be arsed to go dig them up again. See my recent twitter stream for some of them.]

1) Ubuntu 9.10 Karmic

All the xen-tools and stuff install nicely from the repository, but there is no Xen kernel provided. None. At all. You have to go wading through Debian documentation and try installing a Debian Lenny kernel, and it all goes horribly wrong. Also Karmic introduces GRUB2, so all those HOWTO documents that talk about editing /boot/grub/menu.lst are now out of date because GRUB2 is a lot more complex (cf: /etc/rc1.d/). The Canonical Ubuntu forums refer to tickets complaining about the Debian Lenny kernels, and that Ubuntu should not adopt the Debian Xen kernels but roll their own. They have not yet done this.

2) Debian Lenny

Installs quite nicely and cleanly. Xen enables easily – install Xen kernel and reboot – but your framebuffer gets eaten so X11 no longer works (and puts-up interactive warnings on screen to tell you so, so you have to be around to press return a few times) – and then the out-of-the-box config does not appear to work with any of the prebuilt Xen images from Stacklets.com. Messages about “waiting for vif.1 to become free” (when you are using NAT?) and that domUs are dying immediately upon creation and without diagnostics resulting, does not lend confidence.

3) CentOS 5.4

Installs quickly from DVD, and “virtualization” (Xen) is selected easily from the installer menu. The resulting Xen kernel panics on first reboot, due to lack of PAE hardware and that Centos has assumed PAE is available. Can progress no further on the hardware available.

None of this bodes well for Xen in my opinion; I know they are owned by Citrix now, so there should be money behind them, and my feeling is that if they want to be more than a niche player in the increasingly commoditised virtualisation market[1] they should throw money and an engineer at Canonical and make Ubuntu work as a turnkey solution.

[1] I have heard at least 4 people tell me to “use KVM it’s the future” – but (a) I heard that about KDE and (b) that’s not what I am trying to achieve, the point of messing with Xen is to grow familiarity around its supposedly portable technology, not least because EC2 is Xen.

3 Replies to “Experiences with #Xen on #Linux : SUCKAGE ANALYSIS”

  1. Xen has been a second class citizen in Ubuntu for a long while, in fact I don’t think Xen ever really worked that well on Ubintu!

    I’ve not played with KVM but I’ve heard it is good from people I respect. It strikes me that loading some old realtime OS on baremetal and having to reimplement QoS etc and all over again rather than using the existing kernel and tools is a mess and that Xen is an proof of concept carried way too far on a wave of hype and (justified) fear of VMWare dominance.

    That said I played with Citrix Xen Center and was impressed … if you have dedicated modern servers and need to do plain old server consolidation it’s really nice (and the free version does A LOT). I’ve no doubt that the Red Hat and Solaris implementations will also be technically interesting … but I fear Xen has a niche future for the very reasons you are struggling with.

    Users need to be able to install a free client on Windows (yes windows) create a VM, copy it to a suitable server and start a VM. They don’t want to dick about with dual booting Linux on their PC or building kernels. This is what makes Virtual Box (and to a lesser extent VMWare) so great. It’s possible to use Virtual Box (or even VMWare or Virtual PC) to make images and get them working in Xen, but it a PITA.

    If your are interested in portability between VM hosts like EC2 you should read up on Eucalyptus. It should let you make a box look like EC2 (or at least a sub set) and it can use either KVM or Xen as a back end mechanism to run VM images. KVM does well here since it can import Xen and Amazon image formats. I understand you can even use the EC2 firefox plugins to talk to the system … good for testing and playing.

    Ubuntu bundles Eucaliyptus and KVM and they are making a fair bit of noise about how easy and great it is … maybe it’s worth a try? I’d love to know if it works!

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