Thursday, April 19, 2012

rsyslog templates & json

I today added a simpler method to specify JSON inside rsyslog templates. The new method simplifies specifying JSON-encoded fields. It still looks a bit ugly, but if you look closely enough, you'll quickly notice that it no longer needs "quoting magic" and thus is far easier to work with.

Previously, you had to define a template like this:

$template tpl, "{\"message\":\"%msg:::json%\",\"fromhost\":\"%HOSTNAME:::json%\",\"facility\":\"%syslogfacility-text%\",\"priority\":\"%syslogpriority-text%\",\"timereported\":\"%timereported:::date-rfc3339%\",\"timegenerated\":\"%timegenerated:::date-rfc3339%\"}"

The template given above is the default for ElasticSearch. With the new code, this can be replaced by:

$template tpl,"{%msg:::jsonf:message%,%HOSTNAME:::jsonf:fromhost%,%syslogfacility-text:::jsonf:facility%,%syslogpriority-text:::jsonf:priority%,%timereported:::date-rfc3339,jsonf%,%timegenerated:::date-rfc3339,jsonf%}"

It's a bit shorter, but most importantly the JSON field is now generated by the property itself. This is triggered by the "jsonf" (json field) option. If it is given, a

"fieldname"="value"

is automatically generated. The fieldname is either the forth parameter (see "message" in the msg field in the example above) or, if not given, defaults to the property name. If I hadn't insisted on specific field names, I could have written the sample as such:

$template tpl,"{%msg:::json%,%HOSTNAME:::jsonf%,%syslogfacility-text:::jsonf%,%syslogpriority-text:::jsonf%,%timereported:::date-rfc3339,jsonf%,%timegenerated:::date-rfc3339,jsonf%}"

Note that the commas to separate the various JSON fields must still be included inside the template as literal text.

This new system works pretty well within the current template system. The config format will probably become a bit more intuitive when moving it over to the new config language. But the exact how's of that are still to be decided. In fact, I think this string-based way of specifying templates is not so bad. In any case, I am also considering a template option which would take a template of pure field lists and generate proper JSON out of that. But that's work for another day (or so ;)).

This is to be released with 6.3.9 and already available via the git master branch.
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