Current state: "Under Discussion"
Discussion thread: TBD
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When groups are described, the DescribeGroupsResponse contains the metadata (also known as subscriptions) of the members but the metadata is not surfaced in the KafkaAdminClient#describeConsumerGroups method of the Admin Client. Surfacing the metadata is quite useful when it come to troubleshooting a consumer group (e.g. in the context of KIP-496). As the information is already in the protocol, it makes sense to expose it via the Admin Client.
The metadata method is added to the MemberDescription class and returns the metadata of the group member. The metadata is only computed when the group is a consumer group similarly to the existing assignment method.
The MemberMetadata is added and represents the metadata of the group member.
The ConsumerGroupDescription returned by KafkaAdminClient#describeConsumerGroups includes the metadata of each member of the group. The MemberDescription class is extended to carry on the MemberMetadata as described above. The metadata is populated only when the group is a consumer group similarly to the assignments.
Compatibility, Deprecation, and Migration Plan