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Status

Current state: [One of "Under Discussion", "Accepted", "Rejected"]

Discussion thread: TBDhere [Change the link from the KIP proposal email archive to your own email thread]

JIRA: here [Change the link from KAFKA-1 to your own ticket]

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Describe the problems you are trying to solve.

Public Interfaces

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

A public interface is any change to the following:

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Binary log format

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The network protocol and api behavior

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Any class in the public packages under clientsConfiguration, especially client configuration

• org/apache/kafka/common/serialization

• org/apache/kafka/common

• org/apache/kafka/common/errors

• org/apache/kafka/clients/producer

• org/apache/kafka/clients/consumer (eventually, once stable)

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Monitoring

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Command line tools and arguments

Under static membership, client user could provide a list of hard-coded `group.instance.id` so that the server could respond to scaling operations more intelligently. For example when we scale up the fleet by defining 4 new client instance ids, the server shall wait until all 4 new members to join the group before kicking out the rebalance, same with scale down. This change requires us to change JoinGroup protocol to batch mode in order to enable admin request to easily scale.

JoinGroupRequest => GroupId SessionTimeout RebalanceTimeout MemberId GroupInstanceId ProtocolType GroupProtocols
  GroupId             => String
  SessionTimeout      => int32  // removed
  RebalanceTimeout    => int32  // removed
  MemberId            => String // removed
  GroupInstanceId     => String // removed
  ProtocolType        => String 
  GroupProtocols      => [Protocol MemberMetadata]
  Protocol            => String // removed
  MemberMetadata      => bytes // removed
  JoinGroupMembers    => []JoinGroupRequestMember // new
						   SessionTimeout      => int32  // new
						   RebalanceTimeout    => int32  // new
 						   MemberId            => String // new
						   GroupInstanceId     => String // new
						   Protocol            => String // new

JoinGroupResponse => ThrottleTime ErrorCode GenerationId ProtocolName LeaderId MemberId Members
  ThrottleTime           => int16
  ErrorCode              => int16  // removed
  GenerationId           => int32
  ProtocolName           => String
  LeaderId               => String
  MemberId               => String // removed
  Members                => []JoinGroupResponseMember 	
							MemberId         => String
                            GroupInstanceId  => String
                            Metadata         => bytes
  MemberJoinResponseList => []JoinGroupResult  // new
							MemberInfo 	=> JoinGroupResponseMember	
							ErrorCode   => int16

Public Interfaces

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Proposed Changes

Describe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.

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