[Backport 2.x] [Segment Replication ] Add shard routing primary check when processing a checkpoint.

CHANGELOG.md

@@ -87,7 +87,8 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - [Segment Replication] Extend FileChunkWriter to allow cancel on transport client ([#4386](https://github.com/opensearch-project/OpenSearch/pull/4386))
 - [Segment Replication] Fix NoSuchFileExceptions with segment replication when computing primary metadata snapshots ([#4366](https://github.com/opensearch-project/OpenSearch/pull/4366))
 - [Segment Replication] Fix timeout issue by calculating time needed to process getSegmentFiles ([#4434](https://github.com/opensearch-project/OpenSearch/pull/4434))
-- [Segment Replication] Update replicas to commit SegmentInfos instead of relying on segments_N from primary shards.
+- [Segment Replication] Update replicas to commit SegmentInfos instead of relying on segments_N from primary shards ([#4450](https://github.com/opensearch-project/OpenSearch/pull/4450))
+- [Segment Replication] Adding check to make sure checkpoint is not processed when a shard's shard routing is primary ([#4716](https://github.com/opensearch-project/OpenSearch/pull/4716))
 
 ### Security
 

server/src/main/java/org/opensearch/index/shard/IndexShard.java

@@ -1432,6 +1432,10 @@ public final boolean shouldProcessCheckpoint(ReplicationCheckpoint requestCheckp
             logger.warn("Ignoring new replication checkpoint - shard is in primaryMode and cannot receive any checkpoints.");
             return false;
         }
+        if (this.routingEntry().primary()) {
+            logger.warn("Ignoring new replication checkpoint - primary shard cannot receive any checkpoints.");
+            return false;
+        }
         ReplicationCheckpoint localCheckpoint = getLatestReplicationCheckpoint();
         if (localCheckpoint.isAheadOf(requestCheckpoint)) {
             logger.trace(

server/src/test/java/org/opensearch/index/shard/SegmentReplicationIndexShardTests.java

@@ -62,6 +62,7 @@
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
+import static org.mockito.Mockito.spy;
 
 public class SegmentReplicationIndexShardTests extends OpenSearchIndexLevelReplicationTestCase {
 
@@ -208,6 +209,36 @@ public void testPublishCheckpointAfterRelocationHandOff() throws IOException {
         closeShards(shard);
     }
 
+    /**
+     * here we are starting a new primary shard and testing that we don't process a checkpoint on a shard when it's shard routing is primary.
+     */
+    public void testRejectCheckpointOnShardRoutingPrimary() throws IOException {
+        IndexShard primaryShard = newStartedShard(true);
+        SegmentReplicationTargetService sut;
+        sut = prepareForReplication(primaryShard);
+        SegmentReplicationTargetService spy = spy(sut);
+
+        // Starting a new shard in PrimaryMode and shard routing primary.
+        IndexShard spyShard = spy(primaryShard);
+        String id = primaryShard.routingEntry().allocationId().getId();
+
+        // Starting relocation handoff
+        primaryShard.getReplicationTracker().startRelocationHandoff(id);
+
+        // Completing relocation handoff.
+        primaryShard.getReplicationTracker().completeRelocationHandoff();
+
+        // Assert that primary shard is no longer in Primary Mode and shard routing is still Primary
+        assertEquals(false, primaryShard.getReplicationTracker().isPrimaryMode());
+        assertEquals(true, primaryShard.routingEntry().primary());
+
+        spy.onNewCheckpoint(new ReplicationCheckpoint(primaryShard.shardId(), 0L, 0L, 0L, 0L), spyShard);
+
+        // Verify that checkpoint is not processed as shard routing is primary.
+        verify(spy, times(0)).startReplication(any(), any(), any());
+        closeShards(primaryShard);
+    }
+
     public void testReplicaReceivesGenIncrease() throws Exception {
         try (ReplicationGroup shards = createGroup(1, settings, new NRTReplicationEngineFactory())) {
             shards.startAll();