[dnsdist] query multiplication for enhanced reliability, response times

[bert hubert]

Hello everyone,

As the dnsdist installed base grows (a recent large addition is 'quad9.net',
https://arstechnica.com/information-technology/2017/11/new-quad9-dns-service-blocks-malicious-domains-for-everyone/
) we are getting more and more requests for something we previously did not
want to do: query multiplication.

dnsdist currently takes 1 incoming query packet and hands it to 1 backend.
It will not repeat queries if the response is slow or not forthcoming.

Various deployments however have backends with suboptimal networks, or want
to improve response times by opportunistically asking several backends.  An
idea that has also been raised is to utilize 'cache snooping' (rd=0) for
this purpose.

With this message, we invite everyone to share their requirements for query
multiplication.  We are attempting to deliver something in quite short
order, but we'd like to make sure we actually develop the functionality that
people need.

If you have needs, please share them here. Should you feel uncomfortable
doing so in public, you can also email powerdns.ideas at powerdns.com off
list and we can include your requirements anonymously. This does not apply
to support by the way - our procedures for community support are on 
https://blog.powerdns.com/2016/01/18/open-source-support-out-in-the-open/

Thanks!

	Bert