[CentOS] OT: Why VM?

Fri May 27 21:29:19 UTC 2011
Devin Reade <gdr at gno.org>

But taking the other side of the argument, here are two scenarios where
I *wouldn't* use virtualization (one could certainly enumerate more):

1. A production DB server or server cluster.

2. I've had services where I needed to maximize uptime.  One option
   I tried were VMs and being able to move the VM back and forth
   between hosts.  That might cover hardware failure, but I'd still
   take outages when I needed to upgrade software in the VM.  Moving
   to a traditional HA solution on physical hardware means the outages
   are now measured in seconds instead of minutes, and most of the time
   are undetectable by the users.

   I also tried services where the HA nodes are themselves VMs, but
   was less than impressed with operational stability.

When CentOS 6 comes out, though, I'll be interested to see how (2)
behaves when it comes time to do a rolling upgrade from CentOS 5
(bring a node down, install and reconfigure C6 from scratch, rejoin
the cluster, have C6 take over the services, then upgrade the other

Thank god for test environments.  And backups.