Github user ottobackwards commented on the issue:
https://github.com/apache/nifi/pull/1925
I don't think adding groks, one at a time is very feasible. Also, since
groks can be compound and build on other groks, possibly from other files etc,
having to load every grok in every instance of the controller as a dynamic
property is going to be very tough for the user. Many times you don't just
need one grok, you need many to build up to that one. Thinking of groks as
atomic vs. sets I think is awkward.
If the ui could load one or more files containing groks, and add the
properties from each file for you, that would work... but that still seems
wrong.
The groks should be in the registry, as named grok files possibly
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