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https://issues.apache.org/jira/browse/KAFKA-20971?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18108183#comment-18108183
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Harsh Vasava commented on KAFKA-20971:
--------------------------------------
Confirmed — I checked the broker log directly and it's running trunk, not an
old broker:
[2026-08-25 19:46:58,790] INFO Kafka version: 4.5.0-SNAPSHOT
So the setup is correct: the 4.2.1/4.3.1 Streams client is being run against a
4.5.0-SNAPSHOT (trunk) broker.
For the {{streams_version=4.2.1}} case, the client fails locally before
connecting to the broker. The exact {{streams.stderr}} output is:
Exception in thread "main" org.apache.kafka.common.config.ConfigException:
Streams rebalance protocol does not support static membership. Please set
group.protocol=classic or remove group.instance.id from the configuration.
at
org.apache.kafka.streams.StreamsConfig.verifyStreamsProtocolCompatibility(StreamsConfig.java:1509)
at org.apache.kafka.streams.StreamsConfig.<init>(StreamsConfig.java:1501)
at org.apache.kafka.streams.StreamsConfig.<init>(StreamsConfig.java:1488)
at org.apache.kafka.streams.KafkaStreams.<init>(KafkaStreams.java:815)
at
org.apache.kafka.streams.tests.StaticMemberTestClient.main(StaticMemberTestClient.java:67)
This confirms that the old 4.2.1 client rejects the {{group.protocol=streams}}
+ {{group.instance.id}} combination locally, before connecting to the
4.5.0-SNAPSHOT broker.
> Add cross version system test for "streams" static group membership
> -------------------------------------------------------------------
>
> Key: KAFKA-20971
> URL: https://issues.apache.org/jira/browse/KAFKA-20971
> Project: Kafka
> Issue Type: Test
> Components: streams, system tests
> Affects Versions: 4.4.0
> Reporter: Matthias J. Sax
> Assignee: Harsh Vasava
> Priority: Minor
> Attachments: image-2026-08-26-11-25-57-501.png
>
>
> We added support for static group membership on the "streams" protocol. This
> is a broker side fix, and thus Kafka Streams client 4.3 and 4.2 should also
> be able to use static membership against a 4.4+ broker. But we do not have a
> system test for this.
> We should also have a negative test, that a 4.4+ Kafka Streams client, agains
> an older broker 4.3/4.2 get a clear error message that static membership is
> not supported.
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