Friday, May 19, 2006

Thinking about rewrite rules

Again the question on Solaris message IDs was raised in an email sent to me in private. For those who don't know how a Solaris msgid looks like, look at this example:

May 14 18:51:57 inbound2 su: [ID 366847 auth.notice] 'su root' succeeded

I was asked to include an MSGNOID macro which excludes this msgid in the final destination. The problem I have with this approach is that it simply does not scale: there are simply too many combinations to cover with various macros, an example using the msgid case:
  • a macro that includes neither the name of the program, nor the msgid
  • a macro that includes program name only
  • a macro that includes msgid but not the program name
  • a macro that includes both the program name and the msgid
As you can imagine this quickly becomes a maintenance nightmare even if one finds out a proper name for all of these combinations, especially if you add that other devices have their own extensions to syslog.

What I am pondering is to renew my old ideas about adding sed-like rewrite rules to syslog-ng, something along the lines of:

rewrite r_msgid { msg("s/\[ID [0-9]+ [a-z]+\.[a-z]+\]//");

log { source(s_local); filter(f_noid); rewrite(r_msgid); destination(d_messages); };

Of course similar functionality would be added to manipulate all syslog message parts, like hostname. The results would become part of the message itself, thus macros would use the rewritten message. And by the way backreferences could be used to refer various parts of the message, matched by regexps.

What do you think?


Anonymous said...

sed-like rewrite rules is a feature I would very much like to see in future releases of syslog-ng. it would be an invaluable addition to the product. please consider it!

Anonymous said...

I've found myself wishing I had the rewrite capabilities at times, but my own testing showed that regular expressions slow down syslog-ng too much when under heavy load:

I think that people will find this incredibly useful and it'll drive further adoption of syslog-ng, but at the same time it'll be the constant source of performance complaints on the mailing list

Just my $0.02.


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