DNSTAP output file rolling trouble in BIND 9.12.0rc1

Alan Clegg alan at clegg.com
Tue Jan 2 20:30:19 UTC 2018


Looks like something that ISC would like to have logged as a bug...  And
a perfect thing to find in rc1. 8-)

AlanC

On 1/2/18 3:00 PM, Jay Ford wrote:
> I'm having some odd trouble with DNSTAP output file rolling in BIND
> 9.12.0rc1.
> 
> I have named built like:
>    BIND 9.12.0rc1 <id:f9c3aba>
>    running on Linux x86_64 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt25-1
> (2016-03-06)
>    built by make with 'STD_CDEFINES=-DISC_FACILITY=LOG_LOCAL5'
> '--libdir=/usr/lib/x86_64-linux-gnu' '--with-openssl' '--enable-dnstap'
> '--enable-fixed-rrset' '--disable-openssl-version-check'
> '--with-libtool' '--enable-dnsrps'
>    compiled by GCC 6.3.0 20170516
>    compiled with OpenSSL version: OpenSSL 1.1.0f  25 May 2017
>    linked to OpenSSL version: OpenSSL 1.1.0f  25 May 2017
>    compiled with libxml2 version: 2.9.4
>    linked to libxml2 version: 20904
>    threads support is enabled
> 
> I have DNSTAP configured like:
>    dnstap {
>       client query;
>    };
>    dnstap-output file "tmp/dnstap.out" versions 10 size 10m;
> 
> It mostly works as expected, except that named:
>    o  logs twice about rolling the file every time, such as:
>          Jan  2 05:15:42 named[24758]: dnstap: info: rolling dnstap
>             destination 'tmp/dnstap.out'
>          Jan  2 05:15:42 named[24758]: dnstap: info: rolling dnstap
>             destination 'tmp/dnstap.out'
>    o  sometimes crashes after logging that, possibly after rolling the file
>    o  writes to multiple output files simultaneously, such as:
>          ls -lt dnstap* | head -2
>          -rw-r--r-- 1 bind bind  1282048 Jan  2 16:24 dnstap.out
>          -rw-r--r-- 1 bind bind  1273856 Jan  2 16:24 dnstap.out.0
>       & 2 minutes later:
>          ls -lt dnstap* | head -2
>          -rw-r--r-- 1 bind bind  1286144 Jan  2 16:26 dnstap.out
>          -rw-r--r-- 1 bind bind  1277952 Jan  2 16:26 dnstap.out.0
> 
> This system had 4 worker threads in use.  Another similar system with
> only 1 thread does not have such trouble, which got me wondering about
> problems with threads & DNSTAP, specifically output file rolling. 
> Reducing the threads on the afflicted system (via named option "-n 1")
> seems to avoid the problem, but it's a little early to tell, & it's not
> a desirable fix.
> 
> I'd appreciate it if somebody who knows the code would comment on the
> threads vs DNSTAP possibility or point me in some other direction to
> figure this out.
> 
> I have a named core file & can provide more config... details if required.
> 
> ________________________________________________________________________
> Jay Ford, Network Engineering Group, Information Technology Services
> University of Iowa, Iowa City, IA 52242
> _______________________________________________
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