[Gllug] best way to update a single production server?

[John Hearns]

As everyone else has said, if you only have one server and it MUST be
up 24/7 you're on a losing streak.
At the very least it must have N+1 PSUs, a UPS on one of the PSUs (not
them all!) plus mirrored system disks.
Plus duplicate network cards with some sort of failover. Plus
multipathing to any SAN fibre connections.
Need I go on?

Anyway, just would like to dredge something out of the past - the Two
Kernel Monte.

This was used in the Scyld Beowulf machines to swap between the kernel
which booted the machines up and the final one which the machines
would run.
http://www.linux.org/apps/AppId_2547.html

Don't try this at home. In fact, don't try it at all.
But it would be a cute way to do your kernel upgrades without downtime!


ps. thinking about this, does Xen live migration (or similar VM live
migration) work between machines with differing kernel versions?
I guess google is my friend, but would be interested if anyone has
direct experience of this scenario.
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