Observe how partition assignments change when consumers join or leave a group.
A consumer group rebalance reassigns partition ownership among group members. In the classic (eager) protocol, ALL consumers pause fetching during rebalance. With cooperative rebalancing, only affected partitions move. Understanding rebalances is critical for production consumer health.
The steps below reference the interactive simulator, which is being migrated into /simulate next — until it lands, treat this as the written runbook for the exercise.
Steps
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Verification
Total partitions handled = 3, regardless of consumer count. Consumers > partitions means idle standbys.
The interview angle
Key answer: each partition → exactly one consumer per group. Max active consumers = partition count. Static membership (group.instance.id) reduces rebalances on K8s restarts.