[9fans] DHCP

[presotto@plan9.bell-labs.com]

I'm about to replace the current file system based state sharing in
dhcpd with the one from the internet draft:

  "DHCP Failover Protocol", Ralph Droms, Bernard Volz, K. Kinnear, Arun
  Kapur, Mark Stapp, Greg Rabil, Mike Dooley, Steve Gonczi, 01/24/2002,
  <draft-ietf-dhc-failover-10.txt>

The current dhcpd addresses the case of a single cpu falling over, but
has a single point of failure if we lose the shared file server all
the servers are running from.

The IETF draft separates the address space so that each server only serves
from its own pool of addresses but updates the others' state through
a special protocol so that each can take over should its partner fail.
I'm a bit bothered that it only supports 2 servers but maybe I'm
being silly.

Another possible solution would be to use the current dhcpd but run it
on top of either
(1) a very reliable file server (venti?)
or
(2) a replicated file service that runs on all the servers' machines.

I don't really have (1) though venti might get there.
I know how to do (2) but then I'ld have to handle
inconsistencies and the solution looks like it'll
get so dhcp dependent that I should just go with the
draft standard.

Any comments?  Someone already done it or something better?
I'm going to start on the draft version but I have nothing
against stopping or changing it later.