[dns-operations] Forcing BIND to randomly expire records from cache ahead of time

[Mark Andrews]

In message <53B5D364.2050403 at gmail.com>, Tim Wicinski writes:
> 
> Mark
> 
> Unbound has this feature, but its' a % of the TTL (oh they may of 
> changed this).
> 
> You may be also interested in this idea which was floated during IETF, 
> and not rejected, just a small sliver of useful customer base:
> 
> http://tools.ietf.org/id/draft-wkumari-dnsop-hammer-00.txt

Bind also has hammer support (prefetch) 9.10.

But with my understanding of the problem, neither will help as the
queries are not consistantly occuring (like queries for facebook
or google are) but are periodic.

Mark

> On 7/3/14 5:06 PM, Mark Pettit wrote:
> > Hi, folks.
> >
> > I have an issue with BIND cache timeouts, and I was hoping someone else
> > might have some idea how to fix this.
> >
> > Here's the situation: we have a large number of servers that do a huge
> > number of DNS lookups at the top of every minute. The TTL for the
> > records they're looking up is 3600.
> >
> > What we've noticed is that on a host with a recently-restarted copy of
> > BIND, we see huge spikes in DNS latency every 61 minutes. This makes
> > logical sense, given the behavior of the DNS lookups.
> >
> > What is more interesting is that on hosts that have been running BIND
> > for a very long time (on the order of months), the spikiness is not visible
> .
> >
> > Our speculation is that over time, due to the interaction between the
> > 3600 TTL and the "once every minute" lookup behavior, cache misses
> > become randomly distributed throughout the hour, and don't cause the
> > spiky behavior that is observed initially.
> >
> > One of our ideas to resolve this is to randomize the TTLs in the zone
> > files, causing them to expire out of cache at different times, thus
> > forcing more-rapid distribution of cache misses across the hour.
> >
> > However, this would involve some massive edits to our zone files, and
> > isn't really ideal.
> >
> > What *would* be ideal would be if we could tell BIND to randomly expire
> > some small percentage of cached entries ahead of the actual TTL
> > expiration. This would serve the same purpose as assigning "random" TTLs
> > to the actual records in the zone files.
> >
> > Does BIND have a config option like this? Has anyone else ever
> > encountered this issue, and if so, how did you address it?
> >
> > Thanks for any advice, and I hope everyone has a fantastic Fourth of
> > July weekend.
> >
> > Mark Pettit
> >
> >
> >
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org