Failed to load appender in elasticsearch - logging yml syntax

I am looking for the help with elasticsearch logging.yml. I don't have much experience with Java. Any help would be appreciated.

I tried to add roller-log4j ( into my elasticsearch. I built roller-log4j with maven and place the built jar file into elasticsearch lib directory. When starting Elasticsearch get log4j:WARN Error during default initialization.

My logging.yml looks like:

type: com.github.rollbar.log4j.RollbarAppender layout: type: org.apache.log4j.PatternLayout ConversionPattern: "%d{yyyy-MM-dd HH:mm:ss} [%t] %-5p %C:%L - %m%n"
The console output from Elasticsearch:

`log4j:WARN Continuable parsing error 19 and column 16
log4j:WARN The content of element type "appender" must match "(errorHandler?,param*,rollingPolicy?,triggeringPolicy?,connectionSource?,layout?,filter*,appender-ref*)".
log4j:WARN Error during default initialization java.lang.NoClassDefFoundError: org/apache/log4j/AppenderSkeleton at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass( at at