KAFKA-20169: Support static membership for Kafka Streams with the streams rebalance protocol at Client Side. by chickenchickenlove · Pull Request #22559 · apache/kafka

chickenchickenlove · 2026-06-13T02:33:12Z

Summary

This PR adds the remaining client-side support for static membership
when Kafka Streams uses the streams rebalance protocol
(group.protocol=streams) introduced by KIP-1071.

The change allows group.instance.id to be used with the streams
protocol, sends the proper static-member leave epoch when a static
Streams member closes with DEFAULT or REMAIN_IN_GROUP, and treats
UNRELEASED_INSTANCE_ID as a known fatal heartbeat error.

Some close-related changes that were part of my previous full PR
#21603 are intentionally not
included here because they are already covered by
#21579, which introduced
CloseOptions.DEFAULT for Kafka Streams.

Changes

Allow static membership configuration with group.protocol=streams.
Handle UNRELEASED_INSTANCE_ID explicitly in
StreamsGroupHeartbeatRequestManager.
Add coverage for static member close behavior:
- DEFAULT and REMAIN_IN_GROUP use
  LEAVE_GROUP_STATIC_MEMBER_EPOCH.
- LEAVE_GROUP uses LEAVE_GROUP_MEMBER_EPOCH.
- pollOnClose sends the static leave epoch and instance id.
Update Streams config tests to verify group.instance.id is allowed
for unprefixed, consumer., and
main.consumer. configurations.

Reviewers: Lucas Brutschy lbrutschy@confluent.io

Copilot

Pull request overview

This PR completes client-side support for static membership (group.instance.id) when Kafka Streams uses the Streams rebalance protocol (group.protocol=streams, per KIP-1071). It removes prior config validation that blocked static membership under the Streams protocol, adds explicit fatal handling for UNRELEASED_INSTANCE_ID in the Streams heartbeat manager, and extends unit tests to cover the expected close/leave-epoch behavior for static members.

Changes:

Allow group.instance.id when group.protocol=streams (including unprefixed, consumer., and main.consumer. configs).
Treat UNRELEASED_INSTANCE_ID as a known fatal error in StreamsGroupHeartbeatRequestManager.
Add/extend unit tests for static-member close semantics and poll-on-close request contents.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
streams/src/test/java/org/apache/kafka/streams/StreamsConfigTest.java	Replaces the previous “should throw” assertion with a parameterized test validating static membership is accepted under Streams protocol and propagated to main consumer configs.
streams/src/main/java/org/apache/kafka/streams/StreamsConfig.java	Removes the Streams-protocol compatibility check that rejected `group.instance.id`, enabling static membership configuration.
clients/src/test/java/org/apache/kafka/clients/consumer/internals/StreamsMembershipManagerTest.java	Adds unit tests ensuring static members use the correct leave epoch on close for DEFAULT/REMAIN_IN_GROUP vs LEAVE_GROUP.
clients/src/test/java/org/apache/kafka/clients/consumer/internals/StreamsGroupHeartbeatRequestManagerTest.java	Extends fatal-error coverage to include `UNRELEASED_INSTANCE_ID` and verifies poll-on-close includes static leave epoch + instance id for static members.
clients/src/main/java/org/apache/kafka/clients/consumer/internals/StreamsGroupHeartbeatRequestManager.java	Adds explicit fatal handling for `UNRELEASED_INSTANCE_ID` in error response processing.

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lucasbru

Thanks for the PR @chickenchickenlove !

lucasbru · 2026-06-16T07:44:33Z

+    @Test
+    public void testStaticMemberRemainInGroupUsesStaticLeaveEpochOnClose() {
+        CloseOptions.GroupMembershipOperation operation = CloseOptions.GroupMembershipOperation.REMAIN_IN_GROUP;
+        MemberState expectedState = MemberState.LEAVING;
+        int expectedEpoch = StreamsGroupHeartbeatRequest.LEAVE_GROUP_STATIC_MEMBER_EPOCH;
+        verifyStaticMemberLeaveOnClose(operation, expectedState, expectedEpoch);
+    }
+
+    @Test
+    public void testStaticMemberDefaultUsesLeaveGroupStaticMemberEpochOnClose() {
+        CloseOptions.GroupMembershipOperation operation = CloseOptions.GroupMembershipOperation.DEFAULT;
+        MemberState expectedState = MemberState.LEAVING;
+        int expectedEpoch = StreamsGroupHeartbeatRequest.LEAVE_GROUP_STATIC_MEMBER_EPOCH;
+        verifyStaticMemberLeaveOnClose(operation, expectedState, expectedEpoch);
+    }
+
+    @Test
+    public void testStaticMemberLeaveGroupUsesLeaveGroupEpochOnClose() {
+        CloseOptions.GroupMembershipOperation operation = CloseOptions.GroupMembershipOperation.LEAVE_GROUP;
+        MemberState expectedState = MemberState.LEAVING;
+        int expectedEpoch = StreamsGroupHeartbeatRequest.LEAVE_GROUP_MEMBER_EPOCH;
+        verifyStaticMemberLeaveOnClose(operation, expectedState, expectedEpoch);
+    }


These three only differ by the operation and expected epoch, could they be a single @ParameterizedTest like testPollOnCloseWhenStaticMemberIsLeaving above? Also the names are inconsistent for the same constant: UsesStaticLeaveEpoch vs UsesLeaveGroupStaticMemberEpoch.

lucasbru · 2026-06-16T07:44:37Z

+        final Metrics localMetrics = new Metrics(time);
+        StreamsMembershipManager membershipManagerWithStaticMember = new StreamsMembershipManager(
+            GROUP_ID,
+            Optional.of("instance-1"),


Minor: this hardcodes "instance-1" while StreamsGroupHeartbeatRequestManagerTest uses an INSTANCE_ID constant. Worth a constant here too for consistency.

lucasbru · 2026-06-16T07:44:41Z

@@ -1600,12 +1600,6 @@ protected StreamsConfig(final Map<?, ?> props,

    private void verifyStreamsProtocolCompatibility(final boolean doLog) {
        if (doLog && isStreamsProtocolEnabled()) {


Now that group.instance.id is accepted with the streams protocol, are there docs that still state static membership isn't supported here? Worth checking the Streams upgrade/config docs so they don't contradict this.

You're right.
There is indeed an issue there as well. I'll address that part too and include it in this PR.

lucasbru · 2026-06-16T07:44:55Z


+    @ParameterizedTest
+    @EnumSource(value = CloseOptions.GroupMembershipOperation.class, names = {"DEFAULT", "REMAIN_IN_GROUP"})
+    public void testPollOnCloseWhenStaticMemberIsLeaving(final CloseOptions.GroupMembershipOperation operation) {


Coverage here is unit-level only. Is there an integration/system test exercising static-member close under group.protocol=streams, or is that expected to come separately?

I was planning to cover this with a Ducktape test.
I'll take a look at the existing integration tests and check whether this can be covered by adding a new test case.

…eams rebalance protocol at Client Side.

chickenchickenlove · 2026-06-22T01:28:23Z

@lucasbru
I've rebased onto latest trunk because CI was failed due to 1password error.
Also, I've addressed them based on your comments.
When you get a chance, please take another look. 🙇‍♂️

github-actions Bot added triage PRs from the community streams consumer clients labels Jun 13, 2026

chickenchickenlove mentioned this pull request Jun 13, 2026

KAFKA-20169: Add ducktape test code for Streams Rebalance Protocol. #22561

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lucasbru requested a review from Copilot June 16, 2026 07:32

lucasbru self-assigned this Jun 16, 2026

lucasbru requested a review from squah-confluent June 16, 2026 07:32

lucasbru mentioned this pull request Jun 16, 2026

KAFKA-20169: Support static membership for Kafka Streams with the streams rebalance protocol at Client Side. #21603

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chickenchickenlove mentioned this pull request Jun 18, 2026

KAFKA-20169: Support static membership for Kafka Streams with the streams rebalance protocol at Server Side. #21565

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chickenchickenlove added 2 commits June 22, 2026 10:11

KAFKA-20169: Support static membership for Kafka Streams with the str…

aa4601a

…eams rebalance protocol at Client Side.

Addressing review.

44d3eb3

chickenchickenlove force-pushed the KAFKA-20169-CLIENT-CORE branch from 5d2ace3 to 44d3eb3 Compare June 22, 2026 01:11

chickenchickenlove requested a review from lucasbru June 22, 2026 01:28

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KAFKA-20169: Support static membership for Kafka Streams with the streams rebalance protocol at Client Side.#22559

KAFKA-20169: Support static membership for Kafka Streams with the streams rebalance protocol at Client Side.#22559
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		@@ -1600,12 +1600,6 @@ protected StreamsConfig(final Map<?, ?> props,

		private void verifyStreamsProtocolCompatibility(final boolean doLog) {
		if (doLog && isStreamsProtocolEnabled()) {

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