The company I work for, Ictivity, recently started testing with Xen(not Xensource!) and HA clustering. There were two case studies, one based on Suse and one based on Red Hat. Both definitely have it’s own advantages and disadvantages but it seemed promising to me. Today I noticed a blog on ONLamp.com about how to set this up. It’s a good read and gives you insight information. You can do this with open source only software so it will not get any cheaper than this. If this solution is suitable for an enterprise environment is definitely a point of discussion, but it is good to see there are more alternatives coming our way.
The idea of using virtual machines to build high available clusters is not new. Some software companies claim that virtualization is the answer to your HA problems, off course that’s not true. Yes, you can reduce downtime by migrating virtual machines to another physical machine for maintenance purposes or when you think hardware is about to fail, but if an application crashes you still need to make sure another application instance takes over the service. And by the time your hardware fails, it’s usually already too late to initiate the migration. So, for each and every application you still need to look at whether you want to have it constantly available, if you can afford the application to be down for some time, or if your users won’t mind having to relogin when one server fails.