[dnsdist] Backend Questions

[Remi Gacogne]

Hello Klaus,

On 07/10/2022 10:53, Klaus Darilion via dnsdist wrote:

> We use dnsdist with 1 single backend server (PDNS). So if this backend 
> is overloaded, dnsdist will detect the backend as DOWN. Hence, the only 
> server for this backend pool down. How will dnsdist behave if all 
> servers for a backend pool are down? Will it stop senden queries to the 
> backend, or will it still send queries to the DOWN server as there is no 
> UP server available?

All of the built-in load balancing policies will stop forwarding queries 
when all the servers in the selected pool are down. It would be possible 
to write a custom load-balancing in Lua that does not do that, of 
course, but I don't think that's what you want in that case.

> So it may be useful to disable healthchecks completely. How can this be 
> done?

You can force a server in the "up" state using the 'setUp()' method, see 
[1].

> My current config is a few years old tested with dnsdist 1.3. These 
> days, dnsdist was faster when I added the listen port multiple times, 
> and also add the single backend server multiple times, to have more 
> receiver threads. For example:
> 
> Is it still (dnsdist 1.6/1.7) useful/necessary to add listenSockets and 
> Backendserver multiple times to improve performance?

I'm afraid so, yes. We have been thinking about a better syntax/design 
for spawning multiple threads without having to duplicate the lines, but 
haven't settled on and implemented a new syntax yet. Ideally we would 
like to avoid breaking compatibility with existing setups, both for the 
configuration files and for the metrics, but we might have to make a 
breaking change in a new major version.

[1]: https://dnsdist.org/quickstart.html#changing-server-settings

-- 
Remi Gacogne
PowerDNS.COM BV - https://www.powerdns.com/

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