private String subAppend(LoggingEvent event) {
    if (this.layout == null) {
      return event.getRenderedMessage();
    } else {
      return this.layout.format(event).trim();
    }
  }
Additional configurations needed before logging to stream. Called once in the container before the first log event is sent.
samza-log4j/src/main/java/org/apache/samza/logging/log4j/StreamAppender.java