[Pdns-users] Possible bug observed in PowerDNS Recursor 3.2.1

[Steve Spencer]

Imre Gergely wrote:
> On 08/04/2010 01:36 PM, Nuno Nunes wrote:
>> Hello all,
>>
>>
>> I've gone through the last few months of the ML, up until the
>> announcement of the release of 3.2.1, and didn't find any reference to
>> this bug I'm apparently seeing, so I'm reporting this to you all for
>> help.
>>
>> I work at an ISP where we have a number of servers running PowerDNS
>> Resolver 3.2.1 as our customer-facing resolvers.
>>
>> We have had this setup for a few months now and sometimes a weird thing
>> happens (and no, I can't reproduce it in any deterministic way and it
>> only happens sometimes): when the TTL for a record of a given zone
>> expires and a new request comes in for it, some of the caches on the
>> farm go out and get the new information, but some others just seem to
>> ignore the TTL and stick with the old data forever.
>> This is most notable when a zone changes name servers and the owner of
>> the zone comes complaining to us that we still have the old data, even
>> after the appropriate amount of time has elapsed for it to have been
>> refreshed (and on these cases we typically observe this behaviour on NS
>> records, but we have observed it on A records also, for example).
>> Now we have had this happen at least three times over the last months
>> and we've tried to narrow it down to a specific set of circumstances,
>> but we haven't been able to really find a pattern.
>> What we do know is that every time this happens, some of the servers
>> behave correctly (TTL expires => get new data) and others don't. And
>> when that happens not even `rec_control wipe-cache` will work.
>> The servers are all identical (same HW, same OS and same SW).
>>
>> Has anyone else observed something like this before? Is it a known bug
>> and I just failed to find it being discussed? More importantly: is there
>> a fix for this behaviour?
> 
> Indeed. I saw the exact same thing, like 3 or 4 times in the last couple
> of months, with the exact same simptoms. Also at an ISP, customers
> complaining about old records after changing nameservers for a domain.
> Couldn't find the cause either, although I did not investigate in
> detail. Good to know I'm not crazy ;)
> 
> I have to look into it next time this pops up with a domain. I have no
> further details unfortunately.
> 
> I don't think it came up until now on the list, it's pretty rare and
> vague to get good details on the problem.
> 
Weird.  I haven't seen it, but then I have a cron job that restarts the
recursor once per week, which probably refreshes anything old at that
point.

-- 
--
Steven G. Spencer, Network Administrator
KSC Corporate - The Kelly Supply Family of Companies
Office 308-382-8764 Ext. 231
Mobile 308-380-7957