How to get random subset of large rrset (30+ IPs for round robin)?

[Warren Kumari]

On Fri, Mar 20, 2020 at 1:04 PM Matus UHLAR - fantomas
<uhlar at fantomas.sk> wrote:
>
> >On Fri, Mar 20, 2020 at 3:14 AM David Klatt <d.klatt at sonnen.de> wrote:
> >> I can't find a way to do the following although I invested plenty of time
> >> in research - maybe you guys have an idea:
> >>
> >> With bind, I'd need to serve a single A record with  30+  IP addresses  and
> >> these addresses have to be returned in random order round robin,
> >> which is done with:
>
> >> Now I'd like bind to just return a  random subset  of e.g. 5 IP addresses
> >> if someone requests this A record.
>
> On 20.03.20 10:37, Warren Kumari wrote:
> >I realize that this is the BIND list, but this sounds like an almost
> >perfect example of PowerDNS's LUA record type (or something with
> >CoreDNS)
> >Other than that, the only thing I can think of is BIND with DLZ and a
> >database that returns a random subset from a DB query, but that sounds
> >awful...
>
> I don't think BIND can do this at all. And I don't think it should...
>
> >> Reason for this are in my case some (thousands) older clients (that I can't control)
> >> that seem not being able to handle that many IPs - the OS resolver just returns an error.
>
> why no use IPVS-like load balancer and hide all hosts behind one or two IPs?
> that would help you much more, amongst others when any of those machines
> fails.

That's almost definitely the right answer, but there *are* cases where
something like what the OP was asking for -  0.pool.ntp.org springs to
mind as one example.
But, yes, a load balancer / anycast is almost definitely going to be a
better choice...

Warren.


>
>
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I don't think the execution is relevant when it was obviously a bad
idea in the first place.
This is like putting rabid weasels in your pants, and later expressing
regret at having chosen those particular rabid weasels and that pair
of pants.
   ---maf