Xen and the Art of Virtualization

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I have historically had several servers at Layered Tech. They recently raised their prices, and the prices for several friends who have hosted servers there. The majority of our use is low volume, experimental sorts of things, and so we decided to go in together on a larger box that we could virtualize.

Enter Voxel, who offer a $199/mo dedicated server that includes:

  • 4 GB RAM
  • Quad XEON 2Ghz
  • 320GB SATA disk (which are growing more standard among these providers, but a lot of options are still IDE
  • SSH-accessible serial console access included

That last one is a serious nod to their foresight and a judo chop to other providers. Layered Tech overs a KVM solution as a $30 or $35/day rental. Voxel automatically includes it.

Anyhow, with this beefy box, we set about setting up Xen. Voxel's support was admirable when my initial xen install broke the serial console access. It turned out my /etc/grub.conf needed a change:

title CentOS (2.6.18-53.1.21.el5xen) root (hd0,0) kernel /xen.gz-2.6.18-53.1.21.el5 com1=9600,8n1 module /vmlinuz-2.6.18-53.1.21.el5xen ro root=LABEL=/ console=tty0 console=ttyS0,9600 panic=100 module /initrd-2.6.18-53.1.21.el5xen.img

(Change in bold)

Without the com1= line, it defaulted to 38400.

Anyhow, with that done, I got to work actually setting up Xen virtual server instances. The host box (aka the Dom0) is CentOS, and so the "easy" install should be another instance of virtualized CentOS, although any variant should be usable. I tried to use virt-install, but it failed miserably.

First, I had issues with networking. Even when I resolved those, halfway through anaconda installing packages, the system crashed.

Ultimately, I settled on doing it manually using this guide to installing CentOS DomUs on a CentOS Dom0.

Caveats for me included the fact that my bridge was virbr0 instead of xenbr0. I have a xenbr0, it just wasn't the correct bridge for RFC1918 going out...

Anyhow, aside from the networking problems, that went fairly smoothly. (Although the top of the guide has you selecting from i386 or x86_64, and the kickstart config just says i386, so I had to restart to correct that, since I was doing the x86_64 install.

Still on the agenda: getting a real IP address. Voxel offered a reasonable extra 8 IPs for $4/mo, and we'd like to ensure each VPS has its own IP address, not 192.168 addresses that translate.

Still, this has been a pretty fun thing so far. I've heard that Xen is what Amazon is using to provide AWS, and I've been learning a lot of new linux tools (like brctl; I'd never had a reason to do linux bridging prior to now, even though I've done it plenty with networking devices).

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September 2010

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About The Author

Matt Wallace is a cloud computing architect, and recovering Web Application Developer working on a large e-commerce site and dabbling in social networking applications. He has recurring dreams of manipulating the real world with jQuery.