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The following commit(s) were added to refs/heads/2.4 by this push:
     new d783a9f  KAFKA-9815; Ensure consumer always re-joins if JoinGroup 
fails (#8420)
d783a9f is described below

commit d783a9f9f697c4df74abdc2a8ee18c533aa0716e
Author: Rajini Sivaram <[email protected]>
AuthorDate: Tue Apr 7 01:00:11 2020 +0100

    KAFKA-9815; Ensure consumer always re-joins if JoinGroup fails (#8420)
    
    On metadata change for assigned topics, we trigger rebalance, revoke 
partitions and send JoinGroup. If metadata reverts to the original value and 
JoinGroup fails, we don't resend JoinGroup because we don't set `rejoinNeeded`. 
This PR sets `rejoinNeeded=true` when rebalance is triggered due to metadata 
change to ensure that we retry on failure.
    
    Reviewers: Boyang Chen <[email protected]>, Chia-Ping Tsai 
<[email protected]>, Jason Gustafson <[email protected]>
---
 .../consumer/internals/ConsumerCoordinator.java    |  5 +-
 .../internals/ConsumerCoordinatorTest.java         | 58 ++++++++++++++++++++++
 2 files changed, 62 insertions(+), 1 deletion(-)

diff --git 
a/clients/src/main/java/org/apache/kafka/clients/consumer/internals/ConsumerCoordinator.java
 
b/clients/src/main/java/org/apache/kafka/clients/consumer/internals/ConsumerCoordinator.java
index b4d9fa5..6b905c5 100644
--- 
a/clients/src/main/java/org/apache/kafka/clients/consumer/internals/ConsumerCoordinator.java
+++ 
b/clients/src/main/java/org/apache/kafka/clients/consumer/internals/ConsumerCoordinator.java
@@ -727,11 +727,14 @@ public final class ConsumerCoordinator extends 
AbstractCoordinator {
 
         // we need to rejoin if we performed the assignment and metadata has 
changed;
         // also for those owned-but-no-longer-existed partitions we should 
drop them as lost
-        if (assignmentSnapshot != null && 
!assignmentSnapshot.matches(metadataSnapshot))
+        if (assignmentSnapshot != null && 
!assignmentSnapshot.matches(metadataSnapshot)) {
+            requestRejoin();
             return true;
+        }
 
         // we need to join if our subscription has changed since the last join
         if (joinedSubscription != null && 
!joinedSubscription.equals(subscriptions.subscription())) {
+            requestRejoin();
             return true;
         }
 
diff --git 
a/clients/src/test/java/org/apache/kafka/clients/consumer/internals/ConsumerCoordinatorTest.java
 
b/clients/src/test/java/org/apache/kafka/clients/consumer/internals/ConsumerCoordinatorTest.java
index 9e6128b..afef951 100644
--- 
a/clients/src/test/java/org/apache/kafka/clients/consumer/internals/ConsumerCoordinatorTest.java
+++ 
b/clients/src/test/java/org/apache/kafka/clients/consumer/internals/ConsumerCoordinatorTest.java
@@ -843,6 +843,64 @@ public class ConsumerCoordinatorTest {
         assertFalse(coordinator.rejoinNeededOrPending());
     }
 
+    /**
+     * Verifies that the consumer re-joins after a metadata change. If 
JoinGroup fails
+     * and metadata reverts to its original value, the consumer should still 
retry JoinGroup.
+     */
+    @Test
+    public void testRebalanceWithMetadataChange() {
+        final String consumerId = "leader";
+        final List<String> topics = Arrays.asList(topic1, topic2);
+        final List<TopicPartition> partitions = Arrays.asList(t1p, t2p);
+        subscriptions.subscribe(toSet(topics), rebalanceListener);
+        client.updateMetadata(TestUtils.metadataUpdateWith(1,
+                Utils.mkMap(Utils.mkEntry(topic1, 1), Utils.mkEntry(topic2, 
1))));
+        coordinator.maybeUpdateSubscriptionMetadata();
+
+        client.prepareResponse(groupCoordinatorResponse(node, Errors.NONE));
+        coordinator.ensureCoordinatorReady(time.timer(Long.MAX_VALUE));
+
+        Map<String, List<String>> initialSubscription = 
singletonMap(consumerId, topics);
+        partitionAssignor.prepare(singletonMap(consumerId, partitions));
+
+        client.prepareResponse(joinGroupLeaderResponse(1, consumerId, 
initialSubscription, Errors.NONE));
+        client.prepareResponse(syncGroupResponse(partitions, Errors.NONE));
+        coordinator.poll(time.timer(Long.MAX_VALUE));
+
+        // rejoin will only be set in the next poll call
+        assertFalse(coordinator.rejoinNeededOrPending());
+        assertEquals(toSet(topics), subscriptions.subscription());
+        assertEquals(toSet(partitions), subscriptions.assignedPartitions());
+        assertEquals(0, rebalanceListener.revokedCount);
+        assertNull(rebalanceListener.revoked);
+        assertEquals(1, rebalanceListener.assignedCount);
+
+        // Change metadata to trigger rebalance.
+        client.updateMetadata(TestUtils.metadataUpdateWith(1, 
singletonMap(topic1, 1)));
+        coordinator.poll(time.timer(0));
+
+        // Revert metadata to original value. Fail pending JoinGroup. Another
+        // JoinGroup should be sent, which will be completed successfully.
+        client.updateMetadata(TestUtils.metadataUpdateWith(1,
+                Utils.mkMap(Utils.mkEntry(topic1, 1), Utils.mkEntry(topic2, 
1))));
+        client.respond(joinGroupFollowerResponse(1, consumerId, "leader", 
Errors.NOT_COORDINATOR));
+        client.prepareResponse(groupCoordinatorResponse(node, Errors.NONE));
+        coordinator.poll(time.timer(0));
+        assertTrue(coordinator.rejoinNeededOrPending());
+
+        client.respond(joinGroupLeaderResponse(2, consumerId, 
initialSubscription, Errors.NONE));
+        client.prepareResponse(syncGroupResponse(partitions, Errors.NONE));
+        coordinator.poll(time.timer(Long.MAX_VALUE));
+
+        assertFalse(coordinator.rejoinNeededOrPending());
+        Collection<TopicPartition> revoked = getRevoked(partitions, 
partitions);
+        assertEquals(revoked.isEmpty() ? 0 : 1, 
rebalanceListener.revokedCount);
+        assertEquals(revoked.isEmpty() ? null : revoked, 
rebalanceListener.revoked);
+        assertEquals(2, rebalanceListener.assignedCount);
+        assertEquals(getAdded(partitions, partitions), 
rebalanceListener.assigned);
+        assertEquals(toSet(partitions), subscriptions.assignedPartitions());
+    }
+
     @Test
     public void testWakeupDuringJoin() {
         final String consumerId = "leader";

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