Add configurable setting for 4lw.commands.whitelist

[mikebin]

https://github.com/confluentinc/kafka-images/blob/master/zookeeper/include/etc/confluent/docker/zookeeper.properties.template does not currently support configuring 4lw.commands.whitelist. It can alternatively be done with a JVM system property, so this isn't a blocker, but would be useful to have a configurable settings for this: ZOOKEEPER_4LW_COMMANDS_WHITELIST

[ankon]

I'm hitting the same issue when trying to configure a development environment, some more context for making this pop up higher in Google:

$ echo mntr | nc localhost 2181
mntr is not executed because it is not in the whitelist.

Looking at the logs:

[2020-05-25 14:16:23,984] INFO The list of known four letter word commands is : [{1936881266=srvr, 1937006964=stat, 2003003491=wchc, 1685417328=dump, 1668445044=crst, 1936880500=srst, 1701738089=envi, 1668247142=conf, -720899=telnet close, 2003003507=wchs, 2003003504=wchp, 1684632179=dirs, 1668247155=cons, 1835955314=mntr, 1769173615=isro, 1920298859=ruok, 1735683435=gtmk, 1937010027=stmk}] (org.apache.zookeeper.server.command.FourLetterCommands)
[2020-05-25 14:16:23,984] INFO The list of enabled four letter word commands is : [[srvr]] (org.apache.zookeeper.server.command.FourLetterCommands)

(This is from confluentinc/cp-zookeeper:5.4.1)

It can alternatively be done with a JVM system property, so this isn't a blocker

@mikebin I couldn't find how to do that, do you have a pointer/example how do set the system property with the docker images?