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I have twp name servers running PowerDNS as ns1 and ns2 using a master/slave-type setup, and this works well. I want to create multiple servers to provide services (i.e. web, email, etc), then have PowerDNS on either ns1 or ns2 (whichever is hit) return one of several IPs associated with a host name depending on whether that host is actually up and running.

For instance, let's say that I have two web servers, X and Y. I then have two A records in DNS so that webserver.local sometimes resolves to X's IP and sometimes to Y's IP, resulting in a round-robin effect. Perfect.

Now if X goes down, this will still work, but the client will have to time out before they get a chance to hit Y, which means that ultimately they'll get to where they want to go, but just much more slowly. If X goes down, I'd like it's IP address to be removed from the round-robin list of IPs to resolve to so that DNS would only be returning Y's IP when resolving webserver.local, until such time that X is repaired and put back into service.

Asking PowerDNS to verify that the host is up and running on each request could take a second or two (if it's even possible), which would really slow down DNS queries. One thought I've had would be to have a completely separate task periodically through cron check the servers, and modify the PowerDNS configs accordingly. I can certainly attack it from this perspective, but was hoping there might be a more standard way of approaching this that wouldn't require as much custom development.

  • DNS updates always have latency because of caching in many places. Therefore I would approach this problem using virtual IPs and cluster management software, which would assign the virtual IP to a live node. – Tero Kilkanen Nov 14 '14 at 11:00
  • @TeroKilkanen, wouldn't that eliminate my ability to do the above-described round-robin setup then? – Nick Coons Nov 14 '14 at 15:53
  • Yeah, you would need a load balancer to achieve this. If latency doesn't matter for you (few minutes unreachability), then you can set up a script that edits PowerDNS zone information and tells PowerDNS to reload its databases. – Tero Kilkanen Nov 14 '14 at 16:01
  • Why not load balance the web servers, like people that need high availability would normally do? – joeqwerty Nov 14 '14 at 18:35
  • @TeroKilkanen, You're right, I can write a script to do that.. I just wasn't sure if there was a built-in way to handle it that wouldn't require to me to build a script. – Nick Coons Nov 15 '14 at 1:08
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Unable to determine that this was something built into PowerDNS or that there was a more "official" way to handle this, I took the route of building my own program to do this. The program is more of a general "if the host goes down, take a user-defined action" rather than specifically for this so that it has broader applications.

I've made it publicly available in case it's of use to anyone else: https://github.com/hyperionworks/pulse/

  • 1
    This is the right approach! - Peter van Dijk, PowerDNS developer – Habbie Dec 22 '14 at 12:09

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