Hi there, I'm working in a java service that allows managing consumer group's members, specially to pause/resume them on demand. After checking here and there it seems that the actual AdminClient makes this feasible through removeMembersFromConsumerGroup method [ https://kafka.apache.org/38/javadoc/org/apache/kafka/clients/admin/KafkaAdminClient.html#removeMembersFromConsumerGroup(java.lang.String,org.apache.kafka.clients.admin.RemoveMembersFromConsumerGroupOptions)]. The point is that trying to implement the solution, found that somehow the client was returning an error saying something like "unknown member is not found". Jumped to the actual sources to find out the reasons and found that actually the error was accurate, cause the MemberToRemove class is using a static value "JoinGroupRequest.UNKNOWN_MEMBER_ID" for the memberId field that is being used in the member deletion logic, so it is expected that kafka service is responding such thing.
As a PoC, I just updated the code to be able to set a given memberId value (extracted from the describeConsumerGroups method) and it just worked as expected. I created a PR https://github.com/apache/kafka/pull/18738 as a quick explanation to apply to ASF Jira. In that PR I was gently asked to start the conversation through this mailing list, so here we are. I figured out that to make sure that members are not connecting again to the consumer group, we'd require the listener (we're using spring-kafka) to stop trying. Guess it could be done by pausing it from the service code itself, by watching the reason the disconnection happened (this thing we pass on removeMembersFromConsumerGroup). But everything lies on being able to drop the members by setting the proper value as memberId from the admin client. Do you think it makes sense to be able to handle the members like that? Are there any security or kafka-wise service malfunction implications in handling them that way? Thanks in advance,
