Segment Replication stats throwing NPE when shards are unassigned or are in delayed allocation phase

CHANGELOG.md

@@ -15,6 +15,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Add allowlist setting for ingest-common and search-pipeline-common processors ([#14439](https://github.com/opensearch-project/OpenSearch/issues/14439))
 - Create SystemIndexRegistry with helper method matchesSystemIndex ([#14415](https://github.com/opensearch-project/OpenSearch/pull/14415))
 - Print reason why parent task was cancelled ([#14604](https://github.com/opensearch-project/OpenSearch/issues/14604))
+- Fix Segment Replication stats throwing NPE when shards are unassigned or are in delayed allocation phase ([#14580](https://github.com/opensearch-project/OpenSearch/pull/14580))
 
 ### Dependencies
 - Bump `org.gradle.test-retry` from 1.5.8 to 1.5.9 ([#13442](https://github.com/opensearch-project/OpenSearch/pull/13442))

server/src/main/java/org/opensearch/index/seqno/ReplicationTracker.java

@@ -1252,8 +1252,9 @@ public ReplicationCheckpoint getLatestReplicationCheckpoint() {
     }
 
     private boolean isPrimaryRelocation(String allocationId) {
-        Optional<ShardRouting> shardRouting = routingTable.shards()
+        Optional<ShardRouting> shardRouting = routingTable.assignedShards()
             .stream()
+            .filter(routing -> Objects.nonNull(routing.allocationId()))
             .filter(routing -> routing.allocationId().getId().equals(allocationId))
             .findAny();
         return shardRouting.isPresent() && shardRouting.get().primary();

server/src/test/java/org/opensearch/index/seqno/ReplicationTrackerTestCase.java

@@ -134,6 +134,18 @@ static IndexShardRoutingTable routingTable(
         assert activeIds.contains(primaryShard.allocationId());
         final ShardId shardId = new ShardId("test", "_na_", 0);
         final IndexShardRoutingTable.Builder builder = new IndexShardRoutingTable.Builder(shardId);
+
+        // Add a shard that is unassigned to simulate #11945
+        builder.addShard(
+            TestShardRouting.newShardRoutingWithNullAllocationId(
+                shardId,
+                null,
+                null,
+                false,
+                ShardRoutingState.UNASSIGNED
+            )
+        );
+
         for (final AllocationId initializingId : initializingIds) {
             builder.addShard(
                 TestShardRouting.newShardRouting(
@@ -146,6 +158,8 @@ static IndexShardRoutingTable routingTable(
                 )
             );
         }
+
+
         for (final AllocationId activeId : activeIds) {
             if (activeId.equals(primaryShard.allocationId())) {
                 continue;

server/src/test/java/org/opensearch/index/seqno/ReplicationTrackerTests.java

@@ -1214,7 +1214,9 @@ public void testPeerRecoveryRetentionLeaseCreationAndRenewal() {
         IndexShardRoutingTable.Builder routingTableBuilder = new IndexShardRoutingTable.Builder(routingTable);
         for (ShardRouting replicaShard : routingTable.replicaShards()) {
             routingTableBuilder.removeShard(replicaShard);
-            routingTableBuilder.addShard(replicaShard.moveToStarted());
+            if (replicaShard.assignedToNode()) {
+                routingTableBuilder.addShard(replicaShard.moveToStarted());
+            }
         }
         routingTable = routingTableBuilder.build();
         activeAllocationIds.addAll(initializingAllocationIds);

test/framework/src/main/java/org/opensearch/cluster/routing/TestShardRouting.java

@@ -165,6 +165,26 @@ public static ShardRouting newShardRouting(
         );
     }
 
+    public static ShardRouting newShardRoutingWithNullAllocationId(
+        ShardId shardId,
+        String currentNodeId,
+        String relocatingNodeId,
+        boolean primary,
+        ShardRoutingState state
+    ) {
+        return new ShardRouting(
+            shardId,
+            currentNodeId,
+            relocatingNodeId,
+            primary,
+            state,
+            buildRecoveryTarget(primary, state),
+            buildUnassignedInfo(state),
+            null,
+            -1
+        );
+    }
+
     public static ShardRouting newShardRouting(
         String index,
         int shardId,