code: func (l *Log) Fatalf(format string, args ...interface{}) {
  	opts := getLoggerOpts(l.module, api.CRITICAL)
  	if l.loadCustomLogger() {
  		l.customLogger.Fatalf(format, args...)
  		return
  	}
  	l.logf(opts, api.CRITICAL, format, args...)
  	l.deflogger.Fatalf(format, args...)
  }
docs: // Fatalf is CRITICAL log formatted followed by a call to os.Exit(1).