3. Offsets, Consumer Lag, and Rebalancing

A consumer commits an offset to record how far it has processed a partition. Consumer lag is the distance between the latest available offset and the committed or processed offset. Rising lag can indicate slow handlers, insufficient consumers, or downstream failures.

When group membership changes, Kafka rebalances partition assignments. Cooperative assignment and stable instance identities can reduce disruption, but handlers should still tolerate duplicate delivery around commits and rebalances.