How do you view Kafka consumer group lag?

View consumer group lag using the CLI: kafka-consumer-groups.sh --bootstrap-server localhost:9092 --describe --group my-group. This shows LAG, CURRENT-OFFSET, and LOG-END-OFFSET per partition. Programmatically, use AdminClient.listConsumerGroupOffsets() and compare with topic end offsets. For monitoring, expose via JMX (kafka.consumer:consumer-fetch-manager-metrics, records-lag) or use Kafka Exporter for Prometheus. Many teams use Burrow (LinkedIn's open-source lag monitoring tool) for production alerting.

Expected key concepts: kafka-consumer-groups.sh, bootstrap-server, describe, LAG, CURRENT-OFFSET, LOG-END-OFFSET, AdminClient, JMX, Prometheus