Status

Current state: VotingAdopted for 2.6

Vote thread: [Vote] KIP-571: Add option to force remove members in StreamsResetter

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Sometimes people want to reset the stream application sooner but blocked by the left-over members inside the group coordinator, which only expires after session timeout. When the user configures a long session timeout, it could prevent the group from clearing. We should consider adding support to clean up members by forcing them to leave the group. To do that,  

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we could enhance KafkaAdminClient#removeMembersFromConsumerGroup to support remove all members(static&dynamic) in a certain group.

Public Interfaces

Client side changes:

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kafkaAdminClient related changes:

public class RemoveMembersFromConsumerGroupOptions {
	// newly added fieldmethod
	privatepublic boolean removeAll;() {}

	// newly added constructor
	public RemoveMembersFromConsumerGroupOptions(Collection<MemberToRemove> members, Boolean removeAll) {}
}

public class RemoveMembersFromConsumerGroupResult {
	// newly added fields
	private final boolean removeAll;
}

CmdLine API change:

forceOption = optionParser.accepts("force", "Force remove members when long session time out has been configured, please make sure to shut down all stream applications when this option is specified to avoid unexpected rebalances")

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KIP-571 plan to support the ability to force remove members in StreamsResetter, this involves public interfaces changes as below:

• Changes in org.apache.kafka.clients.admin.MemberToRemove 

Previously the KafkaAdminClient#removeMembersFromConsumerGroup only supports to remove members by specifying the groupInstanceId, which means it only supports the removal of static members, so the memberId is added to support removing dynamic members. Since there are two String fields now, new helpers are added and the old constructor will be deprecated.

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1) Changes related to kafkaAdminclient

The old constructor RemoveMembersFromConsumerGroupOptions(Collection<MemberToRemove>members) will imply the non removeAll or remove-specific members scenario and it will throw IllegalArgumentException if empty members is provided.

When the newly added constructor RemoveMembersFromConsumerGroupOptions() is used, it implies the removeAll scenario, underlyingly it set field members to an empty set and removeAll() will return true, in this case, KafkaAdminClient#removeMembersFromConsumerGroup will remove all members in the given group, it will first query the members of the given group and then issue a LeaveGroupRequest with all members specified. Accordingly, the RemoveMembersFromConsumerGroupResult also adds a new private method removeAll() to imply different handling in RemoveMembersFromConsumerGroupResult#all,memberResult. .Under the removeAll scenario, RemoveMembersFromConsumerGroupResult#memberInfos should be empty, the memberResult() is not applicable, the all() should check if RemoveMembersFromConsumerGroupResult#future 100% succeed, if not, it will throw the first exception captured.

23) Add cmdline option --force to StreamsResetter

While with the new option, the StreamsResetter will force remove all active members by first calling KafkaAdminClient#describeConsumerGroups, then calling KafkaAdminClient#removeMembersFromConsumerGroup with active members list fetched from the first call removeAll specified. All the deleted members' info will be logged out if all removals succeed. Otherwise,  the first member removal error will be thrown. 

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1. Because no classes/method will be removed but only deprecated, this change 1) will be backward compatible
2. The new cmdline option --force is also backward compatible because it's a new feature, if not specified, the StreamsResetter's behavior remains unchanged.

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