[Weighted Shard Routing] Fail open requests on search shard failures

server/src/main/java/org/opensearch/cluster/routing/IndexShardRoutingTable.java

@@ -54,6 +54,7 @@
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
@@ -325,6 +326,7 @@ public ShardIterator activeInitializingShardsWeightedIt(
         final int seed = shuffler.nextSeed();
         List<ShardRouting> ordered = new ArrayList<>();
         List<ShardRouting> orderedActiveShards = getActiveShardsByWeight(weightedRouting, nodes, defaultWeight);
+        List<ShardRouting> orderedListWithDistinctShards;
         ordered.addAll(shuffler.shuffle(orderedActiveShards, seed));
         if (!allInitializingShards.isEmpty()) {
             List<ShardRouting> orderedInitializingShards = getInitializingShardsByWeight(weightedRouting, nodes, defaultWeight);
@@ -352,8 +354,8 @@ public ShardIterator activeInitializingShardsWeightedIt(
                 logger.debug("no shard copies found for shard id [{}] for node attribute with weight zero", shardId);
             }
         }
-
-        return new PlainShardIterator(shardId, ordered);
+        orderedListWithDistinctShards = new ArrayList<>(new LinkedHashSet<>(ordered));
+        return new PlainShardIterator(shardId, orderedListWithDistinctShards);
     }
 
     /**

server/src/test/java/org/opensearch/cluster/structure/RoutingIteratorTests.java

@@ -576,6 +576,16 @@ public void testWeightedRoutingWithDifferentWeights() {
             shardRouting = shardIterator.nextOrNull();
             assertNotNull(shardRouting);
             assertFalse(Arrays.asList("node2", "node1").contains(shardRouting.currentNodeId()));
+
+            weights = Map.of("zone1", 3.0, "zone2", 2.0, "zone3", 0.0);
+            weightedRouting = new WeightedRouting("zone", weights);
+            shardIterator = clusterState.routingTable()
+                .index("test")
+                .shard(0)
+                .activeInitializingShardsWeightedIt(weightedRouting, clusterState.nodes(), 1, true);
+            assertEquals(3, shardIterator.size());
+            shardRouting = shardIterator.nextOrNull();
+            assertNotNull(shardRouting);
         } finally {
             terminate(threadPool);
         }