Load Balancing Question...

Kevin Darcy kcd at daimlerchrysler.com
Tue Apr 25 22:21:50 UTC 2000


If you reduce the TTL on the RRset then the effect of intermediate caching
servers is minimized, the downside being that you increase the query traffic and
just generally be a bad net citizen when you do this. But it may be a perfectly
acceptable approach on a private net or internet. IBM's mainframe
"sysplex" load-balancing product uses 0-TTL A records, for instance, but
presumably you'd only be using this on an intranet, since I don't know anyone
who would trust their IBM mainframe to be directly Internet-connected.

Actually, a bigger problem with my hack was that the weighting information
wouldn't have any way to propagate to slaves. I probably should have implemented
it as a bootfile construct, perhaps an extension to rrset-order. At least then
those folks that synchronize their masters and (pseudo-)slaves via rsync or
whatever would have a chance of preserving the weighting information, although
those that still do "traditional" zone transfers would still be out of luck. My
main point in creating the hack was to see how difficult it would be to
integrate weighting into the actual RR-ordering mechanics of BIND; I wasn't
really positioning this as a long-term solution to people's RR-weighting
requirements. The long-term solution to server-side ordering and/or weighting,
in my opinion, is a new record type or possibly one or more EDNS "option"s the
sole purpose of which is to allow nameservers to propagate this metadata between
themselves.


- Kevin


David R. Conrad wrote:

> Hi,
>
> What is the value of a weighted round robin in an originating server when any
> cache re-orders things as they see fit?
>
> Rgds,
> -drc
>
> Kevin Darcy wrote:
> >
> > As Cricket pointed out, listing an address multiple times won't buy you
> > anything since BIND compresses duplicates. I think what you really want
> > is *weighted* round-robin. This doesn't exist in stock BIND 8 and so far
> > I've seen no indication that it'll be available in BIND 9 either. I
> > implemented a very embryonic form of a "$WEIGHT" zonefile directive for
> > BIND 8 a few weeks ago, but it's definitely not production code...
> >
> > - Kevin






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