Add feature: lua axfr filter in outging requests

[vitalvas]

• Program: Authoritative
• Issue type: Feature request

Short description

I want to replace some records in axfr process to another nameserver.

Usecase

• Create host passive or backup nameservers. (You just need to change the NS to the registry.)
• Replace some records to exclude from the zone of visibility in another nameservers

Description

I want to replace some records in axfr process to another nameserver each operator or another dns clusters. But need save original zone without any modification in local database.

Current function axfrfilter completely suitable for this. Only need to allow its use in outging AXFRs.

[Habbie]

I do need to point out that you could do this with a second PowerDNS instance on the same machine today.

[vitalvas]

I now have to do so. ( But it's too expensive to set up new instances for each such case. And what if you need to use dozens of other servers. This is a big niche to make a mistake.

[Habbie]

Why is it expensive? This instance will just need a few megabytes of memory, and you can use it for many domains by defining a filter script per domain.

[vitalvas]

In order to maintain these bundle - we need to implement this in automation tools. In some cases, you need to configure the dnsdist, because some operators do not know how to work a different port than the 53 port.