Enhancement to compare age difference against dynamic acquired limit setting from remote service like elasticsearch cluster settings

[richard-mauri]

My use case is fairly typical: call age{} in the logstash filter and then compare the target field against some threshold. I could not stand the hard coded magic number limit used in the comparison so I forked the repo and developed a POC enhancment that may result in a subsequent pull request.

I added these config fields:

• "@url" to limit service returning a json response containing a limit field.
  I use elasticsearch cluster settings metadata with great success.
• "@user" "@password" basic auth credentials for the limit service
• "@expired_target" name of a boolean target field to store the results of the age diff against limit field comparison
• "@frequency" how many seconds between scheduled calls the limit service to get the latest limit field (in case it changed).
  @age_limit is an instasnce member to cache the latest limit value.

I used the http_client mixin and I'm folding in the rufus_scheduler gem to do the hard work.

The age class register method makes the http request to the limit service synchronously and starts a periodic schedule to perform the next get request for the age limit.

I am new to logstash and filters and ruby, but so far this is working great.
I have concerns about the statefulness of the class instance member access in a multi worker logstash environment. Out of an abundance of caution I am considering adding require require 'jruby/synchronized' and then including JRuby::Synchronized as per https://github.com/jruby/jruby/wiki/Concurrency-in-jruby

I wonder if this enhancement would be useful as a PR or if I should leave it as a fork or develop a completely new alternative to age.

Thoughts?

[richard-mauri]

Please see: #4