Table of Contents

Status

Current state: Under Discussion

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

Motivation

Today group coordinator will take in unlimited number of join group requests into the membership metadata. There is a potential risk described in

Jira
server ASF JIRA serverId 5aa69414-a9e9-3523-82ec-879b028fb15b key KAFKA-7610

 where too many illegal joining members will burst broker memory before session timeout GC them. To ensure stability of the broker, we propose to enforce a hard limit on the size of consumer group in order to prevent explosion of server side cache/memory.

Public Interfaces

We propose to add a new configuration into KafkaConfig.scala, and its behavior will affect the following coordinator APIs:

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where we shall enforce the group size capping rules upon requests.

Proposed Changes

We shall add a config called group.max.size on the coordinator side.

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• This is backward compatible change.

Rejected Alternatives

Some discussion here proposed other approaches like enforcing memory limit or changing initial rebalance delay. We believe that those approaches are "either not strict or not intuitive" (Quote from Stanislav), compared with group size cap which is very easy to understand and config by end user in the customized manner.