FINALLY!

Please see this blog post for details.

-Chris

What is the plan for migrating hosts over to Xen? AFAIK most of the images you've been using for UML don't even have boot loaders or kernels, this implies a non-trivial migration.

It's a piece of cake. A quick reboot of each host is all that's required.

We'll announce the reboot schedule in the next few weeks. We'll be taking our time with this one.

-Chris

Oh, sweet. As long as the images remain compatible between the two methods a planned reboot doesn't sound like a big deal.

Is there any data showing how much faster Xen is than UML?

I have another question: this obviously won't be available immediately, but you do mention the possibility of custom kernels in the future.

I was messing with cryptsetup on one of the linodes we have at work on friday and had some problems that I believe are due to the userspace tools being out of sync with the kernel. Obviously, if there's still a limited set of Linode-provided images this will still be an issue even under Xen.

What would be very cool is if those machines of Linode's that support hardware virtualization were to allow the native kernels from distros to run. There's overhead associated with this, but it wouldn't be the administrative kind, and I don't think I've ever found my bottleneck on Linode to be waiting for CPU time.

Recent kernels actually support paravirtualization ops, so if the distro kernel supports them too, it might be theoretically possible to run them without emulation overhead.

Beware that older kernels (not including 2.6.1x) have pv_ops but break on SMP; this was one of the showstoppers for xen rollout...

This is fine with me. Partly because I don't care about SMP, but also partly because I doubt anything older than Ubuntu 8.04 will be applicable to my Linode Xen usage.

After further consideration, while I would still ultimately prefer to be able to run arbitrary distros, I think there's a lot of gradations between here and there that would provide most of the functionality I'm currently after, while being significantly easier on the Linode staff.

Specifically:

-I want arbitrary native kernels so I can run stock distro kernels, but Ubuntu's Xen support looks pretty reasonable in 8.04, it's sync'd with their native kernel and I don't imagine most modules care, and on AMD64 the userspace changes required are minimal. I could run that rather than a native kernel.
-If it's stock, I don't need it to be an arbitrary kernel image that I provide. If Linode provides the stock distro kernels in their kernel options, the functionality I'm looking for is provided just as effectively. The initrd is a little trickier because that's generated dynamically, but that should be okay as long as there's a provided initrd that's sufficiently inclusive.

Under this setup, the deployment wizard would default the kernel to "latest Ubuntu 8.04" (or CentOS, or whatever), and then you'd simply run with that distro's stock Xen kernel (or paravirt_ops) kernel. The Linode staff would be able to keep their kernels up to date by keeping a VM of that distro around and patched, and then uploading updated kernels/initrd's as necessary.

Once Xen gets rolled out, do you plan on increasing the number of virtual machines per host, or keeping them the same?

Also, do you have more details on how the conversion will take place? A simple reboot sounds promising but also seems too good to be true. I would like to take advantage of kernel modules for instance, but don't want to have to deal with a full migration.

The contention ratios between the plans will remain the same.

Yup. Just a reboot. What can I say?

There is a "filesystem helper" that runs on boot time on the xen hosts that makes sure your /etc/inittab and /etc/fstab have the correct entries in there for Xen, and will modify those files if they need converting. This is completely automated and no work should be required on your end.

-Chris

When I say 'older' I mean 'older than 2.6.24.3 or thereabouts' The patch to fix it could always be backported though.

Hm... Ubuntu doesn't have an inittab anymore. Is that to handle putting the console in the correct place?

I've been wanting to redo my linode with Fedora 8. I wasn't part of the Xen Beta program; should I wait until the migration over to Xen?

Also, what happens when I "yum update" and a new kernel pops up now or after the Xen migration? Would my linode then use the kernel now of after? I'm not all that familiar with either Xen or UML. I'm familiar with VMWare though.

Linode staff,

Now xen is the future are there any plans to offer other operating systems?

I'd love to use a BSD on my linode.

Same here... I'll even be a beta test subject.