[Openstack-operators] Slow DNS resolver causing problems for OSLO

Marcus Furlong furlongm at gmail.com
Tue Aug 5 01:49:55 UTC 2014

On 5 August 2014 11:34, Jeff Silverman <jeff at sweetlabs.com> wrote:
> George,
> The way DNS works is that the resolver queries the first nameserver listed in /etc/resolv.conf.  That name server has 15 seconds to respond.  Why so long?  Because the name server may have to do a recursive search, and that used to take a lot of time.  If the name server doesn't respond in 15 seconds, then the resolver tries the second name server.  It also has 15 seconds to resolve the name.  If it doesn't respond, then the resolver tries the third name server.   The bottom line is that the resolver may take up to 45 seconds to resolve the name.  That's a long time.

This is configurable using options timeout in /etc/resolv.conf. E.g. setting

   options timeout:2

will cause the timeout to be two seconds, which may be more
appropriate given modern network speeds.


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