You have a Kafka client application that has real-time processing requirements.

For real-time applications, thekey metric to monitor is consumer lag— the difference between thelatest offset on the brokerand thelast committed offset by the consumer.

FromKafka Monitoring Guide:

“Consumer lag is the most important metric for real-time applications. It tells you how far behind the consumer is from the latest data in Kafka.”

B relates to replication, not client responsiveness.

C tracks group membership stability, not data delay.

D tracks input throughput, not processing latency.