The 'UNKNOWN' label appears in the fact tree structure when the monitoring process is unable to find or resolve the MBean specified in the configuration.
In the connectionsStanzaZK_KAFKA_*.cfg file, a source Fully Qualified Name (FQN) is defined. The monitoring process queries the Kafka component for the value of the MBean specified in this source FQN. This value is then displayed in the fact tree structure.
If the Kafka component does not return a value for the requested MBean, the monitoring system marks it as 'UNKNOWN'.
For Kafka Connect, the typical source FQN configured is:
kafka-conn.source.fqn: SERVICE=@bean:kafka.connect:type=app-info,client-id=?#NETADDR=@sjmx.serverAddress#APPL=Kafka-Connectors
Additionally, in the tnt4j.KAFKA.*.properties files, there are two key properties that control the retry mechanism for querying the Kafka component at regular intervals:
source.factory.RetryIntervalSecsource.factory.MaxRetryAttempts