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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.
Proposed Changes
Adding protocol level support for batch join.
Add admin request to utilize this feature.
Public Interfaces
We will bump JoinGroup request/response version to support batch adding members.
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Code Block |
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DescribeGroupRequest => ThrottleTime Groups ThrottleTime => int16 Groups => []DescribeGroups ErrorCode => int16 GroupId => String GroupState => String ProtocolType => String ProtocolData => int16 Members => []DescribedGroupMember MemberId => String GroupInstanceId => String // new ClientId => String ClientHost => String MemberMetadata => bytes MemberAssignment => bytes |
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.
Compatibility, Deprecation, and Migration Plan
- What impact (if any) will there be on existing users?
- If we are changing behavior how will we phase out the older behavior?
- If we need special migration tools, describe them here.
- When will we remove the existing behavior?
Rejected Alternatives
- User needs to upgrade broker to be able to use this new feature. Since we are introducing a new admin API, the change should be backward compatible.
Rejected Alternatives
We could trigger multiple join group requests at the same time without changing JoinGroup protocol. However, considering our change in LeaveGroupRequest, it's hard to handle multiple responses within single admin client request. Changing the protocol to adapt to this change shall be more consistentIf there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.