Consumer threads can consume messages even when their consumer group is not visible in the ApsaraMQ for Kafka console. This happens for one of three reasons.
The consumer uses assign mode
In assign mode, consumers manually assign specific partitions instead of relying on the broker for partition assignment. Consumer threads can consume messages without a consumer group being created in the console.
Fix: Create the consumer group in the ApsaraMQ for Kafka console before you start consumers. Reuse existing consumer groups whenever possible. Exceeding the consumer group limit can affect cluster stability. For more information, see Limits.
Auto creation of consumer groups is enabled
If auto creation is enabled on your ApsaraMQ for Kafka instance, consumer threads can consume messages even without a pre-created consumer group.
Fix: Create the consumer group in the ApsaraMQ for Kafka console in advance, even when auto creation is enabled. This keeps your consumer groups visible and manageable. Reuse existing consumer groups whenever possible. Exceeding the consumer group limit can affect cluster stability. For more information, see Limits.
The consumer group was deleted while consumers were still running
In subscribe mode, if you delete a consumer group while its consumer threads are still active, those threads continue consuming messages as long as no rebalancing is triggered. The consumer group no longer appears in the console, but the threads keep running.
Fix: Stop all consumer threads in a consumer group before you delete it.
If you receive a message accumulation alert for a consumer group that no longer appears in the console, see Why do I still receive alerts about message accumulation for a consumer group after I delete the consumer group?.