Re: A Few Questions

[Geoff Silver <geoff@uslinux.net>]

> What happens when you simply insert A records for the master and the
> backup, in order, and do *not* enable round-robin responses?  The master
> should handle the bulk of the work, and if it's fast enough it should be
> able to completely starve the backup, no?

I *believe* if you just enter two IPs like that in DNS, DNS will round
robin.  The only way I know of running a backup service like that is with
MX records, where you can weight each MX record, and they will be tried in
succession.  If I'm wrong, please someone tell me :-)

> I'd be interested to know why this is so much better than, say, load
> balancing across N+1 servers (that is, you size the server set so that you
> can lose one and still handle the maximum expected load without
> significant delay).  Having a resource which does absolutely nothing
> except in an emergency makes sense if it is, say, a fire extinguisher
> (which has no non-emergency function) but I don't see the sense in having
> redundant equipment stand idle when it could be continuously tested by
> sharing the load.

Suppose you have an office on the east coast and another on the west
coast.  locally, your LAN is 100 Mbps, but your WAN is, say a 512k frame
line.  You therefore want your queries to ALWAYS go to the local LDAP
server.  But, if the local server is down, then you want to use the slow
WAN connection so that things will still keep working.

Just an example.  In reality, load balancing is usually a good idea, but I
want ot make sure if a server goes down, queries aren't sent to it (or if
they are, they will *quickly* be retried on one of the other servers).

-- 
Geoff Silver					<geoff at uslinux dot net>
"If Bill Gates had a nickel for every time Windows crashed...
	Oh wait, he does"