[syslog-ng] Missing one log message when destination unavailable for short period of time.

[Balazs Scheidler]

If you think that's the case, please submit a bug report with details why
you think it is behaving incorrectly.

On Thu, May 7, 2020, 19:51 Ali Shirvani <aj.shirvani at gmail.com> wrote:

> Thanks for your reply, I has been checked the syslog-ng debug console, it
> detected the broken connection, and queue further messages
> and send them when the link is available. But I think it doesn't detect
> link down properly.
>
> On Thu, May 7, 2020 at 10:15 PM Balazs Scheidler <bazsi77 at gmail.com>
> wrote:
>
>> The tcp stack of the host would return success for the first message that
>> follows a tcp connection termination.
>>
>> We have no way of knowing that it was actually sent or not, the host
>> kernel doesn't return this information.
>>
>> Syslog-ng tries to detect connection termination proactively and as long
>> as we don't have a message to write we should detect the closing connection
>> and avoid the loss of the upcoming message. Please check if syslog-ng
>> detects the closing connection, it should report this in its debug log
>> level, look for something like "eof detected on an idle connection".
>>
>> The complete solution to this is application level acknowledgement, which
>> is an extra protocol layer over tcp.
>>
>> Syslog-ng PE has rltp for this purpose but that's a proprietary feature
>> and I found its extra overhead is rarely needed.
>>
>> Bazsi
>>
>> On Thu, May 7, 2020, 19:03 Ali Shirvani <aj.shirvani at gmail.com> wrote:
>>
>>> Hi all,
>>>
>>> I tried to setup simple relay with syslog-ng, it receives log on one
>>> port and forward to the destination. It works fine when destination is
>>> available, but when destination unavailable for a short period of time and
>>> then became available I miss one log entry.
>>>
>>> For example assume that I send simple numbers with logger command to
>>> syslog-ng, from 0 to 100, when I receive 50 on destination I stop its
>>> listener and start it again, in this case the first log entry that I
>>> receive is 52 instead of 51.
>>>
>>> Here is my syslog-ng.conf:
>>>
>>> @version: 3.26
>>>
>>> options {
>>>   time_reopen(5);
>>> };
>>>
>>> source s_network {
>>>   network(
>>>     ip("127.0.0.1")
>>>     port(514)
>>>     transport("udp")
>>>   );
>>> };
>>>
>>> destination d_network {
>>>   network(
>>>     "127.0.0.1"
>>>     port(5514)
>>>     transport("udp")
>>>   );
>>> };
>>>
>>> log {
>>>   source(s_network);
>>>   destination(d_network);
>>> };
>>>
>>> Would you please help me to resolve this issue?
>>>
>>> Regards,
>>> Ali
>>>
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>>>
>>>
>> ______________________________________________________________________________
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>> Documentation:
>> http://www.balabit.com/support/documentation/?product=syslog-ng
>> FAQ: http://www.balabit.com/wiki/syslog-ng-faq
>>
>>
> ______________________________________________________________________________
> Member info: https://lists.balabit.hu/mailman/listinfo/syslog-ng
> Documentation:
> http://www.balabit.com/support/documentation/?product=syslog-ng
> FAQ: http://www.balabit.com/wiki/syslog-ng-faq
>
>
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