[Pdns-users] Overlay or pass-through support in PDNS?

[Aki Tuomi]

On 3 August 2022 6.53.11 UTC, Winfried Angele via Pdns-users <pdns-users at mailman.powerdns.com> wrote:
>Hi Eli,
>
>On 03.08.22 01:43, eli glynn via Pdns-users wrote:
>> I've recently inherited a really ugly mess at my company, involving a muddle of PowerDNS, Route53, NS1, and just about every mixed up interaction you could imagine between them all.
>> 
>> The biggest part of the jumble is the way PowerDNS was used as a poor-mans split horizon - we have a large number of records which point at internal (e.g. 10.x) ranges, with duplicate entries in Route53 AND/OR NS1 (don't ask) usually pointing at routable IPs.  There's a lot of badness beyond just that, but the majority of my pain is from that basic situation.
>> 
>> Because the client systems are pointed at PDNS, and it considers itself authoritative, we're forced to duplicate ALL external records 
>
>Not sure if I got that right, but "clients" may only ask a Resolver (PowerDNS Recursor) and never an Auth (PowerDNS Authoritative).
>
>> (overridden or not) within PDNS, or NXDOMAINs result.  This of course leads to two (or sometimes three) sources of truth for all RRs, and historically the needed due diligence has not been performed to keep them in sync.
>> 
>> Long story short, in order to clean up the mess, I'm hoping to implement an "overlay" in PowerDNS, whereby PDNS only contains the RRs which it needs to override.  If a record would normally be identical to the external value (Route53 or NS1) then rather than duplicating it, I'd like PowerDNS to fail through and do a recursive lookup externally, returning that value to the client.  So basically, if an NXDOMAIN or NODATA would be returned for a zone PDNS considers itself authoritative for, it instead recurses and emits whatever comes back from there.
>> 
>> It seems this should be doable using a `postresolve()` hook, or even better `nxdomain()` combined with `nodata()` to minimize Lua roundtrips.  But I'm having a heckuva time implementing the recursion part.  I can't find any canned tooling within Lua to do something theoretically simple (e.g. what in python you'd do with `import socket ; return socket.gethostbyname("blah")`).  I've also considered writing a custom backend but would prefer to keep things simple if at all possible
>> 
>> I know this is an unusual use-case (though I can see where such an "overlay" could be very useful in a number of scenarios).
>> 
>> Any feedback would be appreciated - suggestions, alternate approaches, or even a flat "you can't do that in PowerDNS" if such is the case - it will save me a lot of cycles if so :)
>
>What about Recursoes "forward-zones" or "forward-zones-file" features? This way you could forward queries for your internal Domain Names to your internal Auhoritative Nameserver.
>
>https://doc.powerdns.com/recursor/settings.html#forward-zones
>https://doc.powerdns.com/recursor/settings.html#forward-zones-file
>
>Winfried
>_______________________________________________
>Pdns-users mailing list
>Pdns-users at mailman.powerdns.com
>https://mailman.powerdns.com/mailman/listinfo/pdns-users

Or you could use dnsdist. See https://dnsdist.org - it is recommended for these kinds of things.
-- 
Aki