[log4perl-devel] Log::Log4perl Recipe of the Week (#18)

[<log...@pe...>]

Welcome to the Log::Log4perl recipe of the week. Today:

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Log::Log4perl Recipe of the Week (#18):

On our server farm, Log::Log4perl configuration files
differ slightly from host to host. Can I roll them all into
one?
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You sure can, because Log::Log4perl allows you to specify
attribute values dynamically. Let's say that one of your
appenders expects the host's IP address as one of its
attributes. Now, you could certainly roll out different
configuration files for every host and specify the value
like

    log4perl.appender.MyAppender    = Log::Dispatch::SomeAppender
    log4perl.appender.MyAppender.ip = 10.0.0.127

but that's a maintenance nightmare. Instead, you can have
Log::Log4perl figure out the IP address at configuration
time and set the appender's value correctly:

        # Set the IP address dynamically
    log4perl.appender.MyAppender    = Log::Dispatch::SomeAppender
    log4perl.appender.MyAppender.ip = sub { \
       use Sys::Hostname; \
       use Socket; \
       return inet_ntoa(scalar gethostbyname hostname); \
    }

If Log::Log4perl detects that an attribute value starts with
something like "sub {...", it will interpret it as a perl
subroutine which is to be executed once at configuration
time (not runtime!) and its return value is to be used as
the attribute value. This comes in handy for rolling out
applications whichs Log::Log4perl configuration files show
small host-specific differences, because you can deploy the
unmodified application distribution on all instances of the
server farm.


Have fun! Until next week.

-- Mike

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# Mike Schilli                    #
# log...@pe...        #
# http://perlmeister.com          #
# http://log4perl.sourceforge.net #
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