[nsd-users] reloading NSD zone configuration

Jelte Jansen jelte at NLnetLabs.nl
Tue Apr 28 08:34:24 UTC 2009

Antti Ristimäki wrote:
> Hi,
> We are also concerned about the length of the service break when adding 
> new zones to the configuration file. When a new slave zone/new slave 
> zones is/are added to the configuration file and the NSD is restarted, 
> how long should it take until NSD continues to serve the previously 
> added zones that already exist in the database? That is, is NSD able to 
> continue to serve the
> previously added zones even if the zone transfers for the new zones have 
> not been completed?

If you restart NSD, with some new slave zones added, it will serve existing 
zones as soon as it is up (i.e. within seconds on most systems, see below for my 
private setup and some very anecdotal timing benchmarks). It will also start to 
transfer the new slave zones, but while it is doing that it already serves 
existing ones.

> In our case, the total amount of zones is a couple of thousands, which 
> is why we'd like to avoid unnecessary restarts and service breaks of 
> NSD. To be able to reload the NSD configuration file without restarting 
> NSD would be a very nice feature for us, too. I know this topic has been 
> discussed quite a lot...

I have a small server at home which is running 18677 zones on a 1Ghz 256MB RAM 
machine. Compiling those into a nsd.db file takes a while (several minutes), but 
restarting nsd itself takes about 7 to 10 seconds. Throwing queries against it 
from the other side i would estimate that 1 or 2 seconds of those are spent 
waiting for the previous process to stop, at which point it is still serving.

We are looking into it (if only because the question comes up about once a week 
now), but my personal guess is that a full reload would not gain that much if 
not implemented really really well, so we want to take a good look at what could 
actually be gained and how before doing anything.


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