[jira] [Created] (KAFKA-20848) Consider to surface group-level misconfigurations client side

["Matthias J. Sax (Jira)" <ji...@apache.org>]

Matthias J. Sax created KAFKA-20848:
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             Summary: Consider to surface group-level misconfigurations client side
                 Key: KAFKA-20848
                 URL: https://issues.apache.org/jira/browse/KAFKA-20848
             Project: Kafka
          Issue Type: Improvement
          Components: clients, consumer, group-coordinator, streams
            Reporter: Matthias J. Sax


With the new KIP-848 based consumer/share/streams groups, many configs moved from the client into the broker.

Some of these config are sent back to the client (as the client really uses them), and we recently started to log them ([https://github.com/apache/kafka/pull/22749] and [https://github.com/apache/kafka/pull/22730]) for improved observability.

However, there is a few more configs which have broker defaults plus group level overwrites, and they are not visible on the client (only describe-config or describe-group would reveal them). At the same time, the broker might overwrite group-level config (clamping to min/max for example), what it not visible either on the client.

For Kafka Streams, we have one hybrid config (client + broker combination) ([https://github.com/apache/kafka/pull/22213]) and introduced and error code in the StreamsHeartbeatResponse to surface a misconfiguration client side.

The ides of this ticket is, to do a similar thing for _all_ group level configs. We would add _all_ effective group config to the HB response for logging, with relogging if changed. Additionally, if a value is clamped, and the set group-config is not the effective config, we return some error code, allowing the client to also log a WARNING about it.

This would be a protocol change, so thus we need a KIP.



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