2011/12/20 Christopher Schultz <ch...@christopherschultz.net>:
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> Simon,
>
> On 12/19/11 11:54 AM, Simon wrote:
>> log4j.appender.file.File=/var/log/webapp.log
>>
>> Thus, there is 3 identical webapps logging into the same log file
>> simultaneously :
>
> It's more likely that the last one wins: the first 2 logs was probably
> lost entirely.
FileAppender docs say that Append=true by default. Though I wonder
what will happen during log rotation.
Anyway entries from three servers in the same log file where they
cannot be distinguished from each other are of little help.
>
>> My hypothesis is that as every webapp log to the same log file from
>> a different JVM (the tomcat instances), there could be some
>> concurrency issues when the rolling from log4j occurs !!!
>
> "Some" issues definitely. You need to change this.
>
>> I would like that each webapp logs to a particular file without
>> having a different log4j configuration packaged in the webapp.war
>> archive. My first idea was to modify the log4j configuration so the
>> webapp will log to the console (stdout) and then find a way to
>> redirect the stdout inside a Tomcat instance to a particular file
>
> That sounds awful: a hack (in log4j config) to go to stdout and then
> another hack (in Tomcat config) to redirect to a file. Yuck.
>
>> Is there a way to mimic this behaviour in Tomcat ?
>
> *Sigh* if you have to, you can use the "swallowOutput" attribute on
> your <Context> definition. Then you have to configure Tomcat's logging
> system to put the logs where you want them.
That is fragile. It depends on who catches the value of System.out
first, Tomcat or a logging framework.
>
> IMO a better idea would be to configure log4j properly. I think you
> have several options:
>
> 1. Modify the log4j.properties file in each WAR file to specify
> the proper filename. You said you didn't want to do this.
>
> 2. Use a log4j.properties file that is outside your WAR file.
> You'll have to figure out how to get your webapp to detect
> the right file so that your 3 separate copies don't end up
> reading the same file and reproducing the same issue described
> above.
>
> 3. In your log4j startup code, set a property based upon some
> configuration or environment (context path?) that can be used
> by log4j during configuration and setup of the logging system.
> I personally favor this approach. If you are running in separate
> JVMs, I think you can use system properties and have those
> replaced by log4j when parsing the configuration file(s).
> Read the documentation to be sure.
>
> 4. Configure log4j to log to syslog, and have syslog take care of
> the file situation. Of course, you'll have to identify each
> separate instance of your webapp if you want to be able to
> sort-out which log came from which source. So, you still
> have to somehow identify these webapps uniquely.
>
5. Configure it to write ${catalina.base}/logs.
(That is if all webapps are on different Tomcat instances, as opposed
to having several different-named webapps on the same Tomcat)
If you want that to be written to /var/logs, you can replace
${catalina.base}/logs with a symlink to /var/logs/instance-N/.
Best regards,
Konstantin Kolinko
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