How to enable zookeeper tracking in drillbit.log

Env:

Drill 1.2

Goal:

How to track when drillbit joins the drill cluster or when drillbit disconnects in drillbit.log.

Solution:

1. Add below entry in conf/logback.xml

  <logger name="org.apache.drill.exec.coord.zk" additivity="false">
      <level value="debug" />
      <appender-ref ref="FILE" />
  </logger>

2. Restart this drillbit.
3. After that, whenever there is zookeeper znodes changes, it will print in this drillbit.log.
For example:

2015-11-04 19:47:02,927 [ServiceCache-0] DEBUG o.a.d.e.c.zk.ZKClusterCoordinator - Cache changed, updating.
2015-11-04 19:47:02,932 [ServiceCache-0] DEBUG o.a.d.e.c.zk.ZKClusterCoordinator - Active drillbit set changed.  Now includes 2 total bits.  New active drillbits:
 h3.poc.com:31010:31011:31012
 h2.poc.com:31010:31011:31012