[Pdns-dev] My Backend Getting called multiple times

[Nikhil Bose]

Hi,

First of all sorry for the late reply.

In my backend I am returning the A record based on either the content or
the shortest path to the client. So if the number of servers whose A record
is returned is increased or more, then my backend will take more time to
return the A record, as the record is generated dynamically, I don't use
DB. Though I am trying to find the feasibility of using and not using any
backend cache, but that is for another point I need to consider.

Also one problem I may face is the PowerDNS cache, as currently its based
on the query and does not take same client into consideration. As this
would have given me an option to return the same A record if the query is
from the same client. Probably for this I need to build my own backend
cache.

Thanks,
Nikhil

On Wed, Nov 21, 2012 at 7:48 AM, Ruben d'Arco <cyclops at prof-x.net> wrote:

> Hi,
>
> PowerDNS does not have a configurable timeout for its backends. If you
> backend is slow, the query response is slow.
> PowerDNS has a query (and packet)cache to make sure the backend isn't
> queried for every incoming.
>
> If you backend only has A records, then simply only respond to those
> lookups. Don't forget that ANY would also include A records. SOA records
> indicate that a zone/domain exists, so you will also need to respond to
> that correctly as well.
>
> Could you also describe what you are trying to do? This way we can suggest
> a good approach.
>
> Regards,
>       Ruben
>
> Nikhil Bose <nikhilbose11 at gmail.com> wrote:
>
> >Thanks Ruben,
> >
> >Also if I am serving only A records from my backend, and if my backend
> >is a
> >bit slow, then is there some place I can set a timeout before PowerDNS
> >calls my lookup.
> >
> >As from the example in Writer's guide, suppose I am only serving A
> >records,
> >but if my backend is slow, PDNS queries again for the A record, that
> >means
> >my else part will hit again if my backend is slow,
> >so is there any timeout I can set before PDNS queries back to my
> >backend.
> >
> >Thanks,
> >Nikhil
> >
> >void lookup(const QType &type, const string &qdomain, DNSPacket *p, int
> >zoneId)
> >  {
> >    if(type.getCode()!=QType::A || qdomain!="random.powerdns.com")  //
> >we only know about random.powerdns.com A
> >d_answer="";                                                  // no
> >answer
> >    else {
> >      ostringstream os;
> >os<<random()%256<<"."<<random()%256<<"."<<random()%256<<"."<<random()%256;
> >      d_answer=os.str();                                           //
> >our random ip address
> >    }
> >  }
> >
> >
> >
> >On Fri, Nov 16, 2012 at 4:29 PM, Ruben d'Arco <cyclops at prof-x.net>
> >wrote:
> >
> >> Hi Nikhil,
> >>
> >> This is by design. PowerDNS will try to get the soa record to see if
> >it is
> >> authorative for the domain. It will also try to move up to the root
> >to see
> >> if a backend is authorative for that. If it is, it will continue with
> >the
> >> actual records it needs.
> >> Also, for things like CNAME and MX, it will try to resolve those as
> >well.
> >>
> >> So, it is normal and canot be avoided. Just implement the fuctions as
> >> described in the backend writers guide and powerdns does the rest for
> >you!
> >>
> >> Regards,
> >>      Ruben
> >>
> >> Nikhil Bose <nikhilbose11 at gmail.com> wrote:
> >>
> >> >Hi All,
> >> >
> >> >First of all thanks for the help provided. As Peter in one of my
> >> >earlier
> >> >queries gave me a pointer and following that it is quite trivial to
> >> >create
> >> >our own Backend in PowerDNS and using getRemote(), I was able to
> >> >retrieve
> >> >the Client's resolver IP.
> >> >
> >> >PowerDNS is indeed quite simple to extend. Thanks for this
> >> >architecture.
> >> >
> >> >I have one problem though. My backend is getting called multiple
> >times.
> >> >Even though I just send a single query using the host command.
> >> >Just to show I put some output statements and these are printed
> >after I
> >> >sent the client query
> >> >
> >> >Here's the console output:
> >> >
> >>
> >>
>
> >>***************************************************************************************
> >> >Nov 16 11:20:26 Creating backend connection for TCP
> >> >Constructor called
> >> >% Nov 16 11:20:26 [bindbackend] Parsing 1 domain(s), will report
> >when
> >> >done
> >> >Nov 16 11:20:26 [bindbackend] parsing 'example.com' from file
> >> >'/etc/bind/example.com.zone'
> >> >Nov 16 11:20:26 [bindbackend] Done parsing domains, 0 rejected, 1
> >new,
> >> >0
> >> >removed
> >> >Constructor called
> >> >Nov 16 11:20:26 About to create 3 backend threads for UDP
> >> >Constructor called
> >> >Constructor called
> >> >Constructor called
> >> >Constructor called
> >> >Constructor called
> >> >Constructor called
> >> >Nov 16 11:20:26 Done launching threads, ready to distribute
> >questions
> >> >Nov 16 11:20:35 Distributor misses a thread (4<5), spawning new one
> >> >looked up
> >> >looked up
> >> >looked up
> >> >looked up
> >> >Constructor called
> >> >Constructor called
> >>
> >>
>
> >>***************************************************************************************
> >> >
> >> >How I can reduce this to a single lookup() call from the PowerDNS to
> >my
> >> >Backend?. Even constructor is called many times. Can this be
> >configured
> >> >anywhere?
> >> >
> >> >Thanks,
> >> >Nikhil.
> >> >
> >> >
> >>
> >>------------------------------------------------------------------------
> >> >
> >> >_______________________________________________
> >> >Pdns-dev mailing list
> >> >Pdns-dev at mailman.powerdns.com
> >> >http://mailman.powerdns.com/mailman/listinfo/pdns-dev
> >>
> >> --
> >> Regards,
> >>           Ruben
> >>
>
> --
> Regards,
>           Ruben
>
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