[Pdns-users] PowerDNS Recursor (+PDNS?) and auto-update of local hostname DNS

Nicholas Williams nicholas at nicholaswilliams.net
Sat Oct 17 20:57:48 UTC 2020

> On Oct 17, 2020, at 3:38 PM, Brian Candler <b.candler at pobox.com> wrote:
> On 17/10/2020 20:54, Nicholas Williams wrote:
>> First, the concern. I run MySQL in master/slave replication mode. I have a master MySQL server that I write to, and the PowerDNS servers connect to the slaves, not the master. Is there some way to tell PowerDNS to send updates to the master, or will I have to change one of the servers to connect to the master and explicitly send updates only to that server?
> For DDNS updates, you'd need a powerDNS server which talks to the master.  It can be hidden from the rest of the Internet, and you can use forward-dnsupdate <https://docs.powerdns.com/authoritative/dnsupdate.html#dnsupdate-configuration-options> on the slaves to forward to the master.
That would be nice, but unless I’m misunderstanding forward-dnsupdates, I don’t think I can use it. I don’t have a “master” DNS server and “slave” DNS servers. I just have several native DNS servers that all query MySQL directly. I rely completely on MySQL replication to distribute DNS updates. So I think I’ll have to send my updates directly to a single DNS server that talks to the master. But maybe I’m wrong.
> There is a howto for the ISC dhcp server here: https://docs.powerdns.com/authoritative/dnsupdate.html#dns-update-how-to-setup-dyndns-rfc2136-with-dhcpd <https://docs.powerdns.com/authoritative/dnsupdate.html#dns-update-how-to-setup-dyndns-rfc2136-with-dhcpd>
> It is of course moot if VyOS doesn't support DDNS updates: e.g. https://forum.vyos.io/t/dhcp-service-and-dns-updates/245 <https://forum.vyos.io/t/dhcp-service-and-dns-updates/245> (but the last post was from 2016)
Yep, I found that DHCPD how-to, and then some other searching led me to instructions on how to apply those configurations to UniFi’s EdgeOS, and then some searching through VyOS’s documentation led me to conclude that you can also do this in VyOS. Hooray! To be certain, I wrote up a forum post to clarify some things and posted it here, if anyone is interested:

https://forum.vyos.io/t/dhcp-multiple-shared-networks-vs-multiple-subnets-global-params-vs-shared-network-params-vs-subnet-params/6045 <https://forum.vyos.io/t/dhcp-multiple-shared-networks-vs-multiple-subnets-global-params-vs-shared-network-params-vs-subnet-params/6045>
>> Second, my question: Is there anyway to customize the queries that PowerDNS uses to update the records? Specifically, I would like to add a flag to records that were added or updated with Dynamic DNS so that my administrative console can differentiate between those and explicit records.
> If the master server is *only* handling DDNS updates, then you should be able to customise the query appropriately.
> https://doc.powerdns.com/authoritative/backends/generic-sql.html#specifying-queries <https://doc.powerdns.com/authoritative/backends/generic-sql.html#specifying-queries>

It might be easier to just do the opposite, and set a flag in my admin console for all domains managed by the admin console, instead of trying to set a flag in PowerDNS dynamic updates.



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