How does Kafka report and expose broker and consumer metrics for monitoring?

Kafka brokers, producers, and consumers all expose a large set of runtime metrics via JMX (Java Management Extensions) by default, covering everything from request latency and throughput to under-replicated partition counts and consumer lag — the same interface most JVM applications use for observability, not a Kafka-specific mechanism.

# run with a JMX exporter agent to expose metrics for Prometheus scraping
-javaagent:/opt/jmx_prometheus_javaagent.jar=7071:/opt/kafka-metrics.yml

A few metrics matter especially for day-to-day health checks: UnderReplicatedPartitions (non-zero means some replica has fallen behind and durability is degraded), RequestHandlerAvgIdlePercent (a broker running consistently low signals it's saturated), and consumer-side lag (covered separately via kafka-consumer-groups.sh --describe, since it isn't a simple JMX broker metric). Because raw JMX isn't directly scrapable by tools like Prometheus, most production setups run a JMX-to-Prometheus exporter agent alongside each broker/client JVM, feeding metrics into standard dashboards (Grafana) and alerting pipelines rather than relying on manual JMX console inspection.