diff --git a/server/src/main/java/org/opensearch/cluster/routing/RoutingNode.java b/server/src/main/java/org/opensearch/cluster/routing/RoutingNode.java
index 123d09246bb7b..62e958777f1bf 100644
--- a/server/src/main/java/org/opensearch/cluster/routing/RoutingNode.java
+++ b/server/src/main/java/org/opensearch/cluster/routing/RoutingNode.java
@@ -48,6 +48,7 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.stream.Collectors;
+import java.util.stream.StreamSupport;
 
 /**
  * A {@link RoutingNode} represents a cluster node associated with a single {@link DiscoveryNode} including all shards
@@ -55,11 +56,85 @@
  */
 public class RoutingNode implements Iterable<ShardRouting> {
 
+    static class BucketedShards implements Iterable<ShardRouting> {
+        private static Map<Boolean, Integer> map = new HashMap<Boolean, Integer>() {{
+            put(true, 0);
+            put(false, 1);
+        }};
+
+        private final LinkedHashMap<ShardId, ShardRouting>[] shards; // LinkedHashMap to preserve order
+
+        BucketedShards (LinkedHashMap<ShardId, ShardRouting> primaryShards, LinkedHashMap<ShardId, ShardRouting> replicaShards) {
+            this.shards = new LinkedHashMap[2];
+            this.shards[0] = primaryShards;
+            this.shards[1] = replicaShards;
+        }
+
+        public boolean isEmpty() {
+            return this.shards[0].isEmpty() && this.shards[1].isEmpty();
+        }
+
+        public int size() {
+            return this.shards[0].size() + this.shards[1].size();
+        }
+
+        public boolean containsKey(ShardId shardId) {
+            return this.shards[0].containsKey(shardId) || this.shards[1].containsKey(shardId);
+        }
+
+        public ShardRouting get(ShardId shardId) {
+            if (this.shards[0].containsKey(shardId)) {
+                return this.shards[0].get(shardId);
+            }
+            return this.shards[1].get(shardId);
+        }
+
+        public ShardRouting add(ShardRouting shardRouting) {
+            return put(shardRouting.shardId(), shardRouting);
+        }
+
+        public ShardRouting put(ShardId shardId, ShardRouting shardRouting) {
+            ShardRouting ret = this.shards[map.get(shardRouting.primary())].put(shardId, shardRouting);
+            if (this.shards[map.get(!shardRouting.primary())].containsKey(shardId)) {
+                return this.shards[map.get(!shardRouting.primary())].remove(shardId);
+            }
+
+            return ret;
+        }
+
+        public ShardRouting remove(ShardId shardId) {
+            if (this.shards[0].containsKey(shardId)) {
+                return this.shards[0].remove(shardId);
+            }
+            return this.shards[1].remove(shardId);
+        }
+
+        @Override
+        public Iterator<ShardRouting> iterator() {
+            final Iterator<ShardRouting> iterator1 = Collections.unmodifiableCollection(shards[0].values()).iterator();
+            final Iterator<ShardRouting> iterator2 = Collections.unmodifiableCollection(shards[1].values()).iterator();
+            return new Iterator<ShardRouting>() {
+                @Override
+                public boolean hasNext() {
+                    return iterator1.hasNext() || iterator2.hasNext();
+                }
+
+                @Override
+                public ShardRouting next() {
+                    if (iterator1.hasNext()) {
+                        return iterator1.next();
+                    }
+                    return iterator2.next();
+                }
+            };
+        }
+    }
+
     private final String nodeId;
 
     private final DiscoveryNode node;
 
-    private final LinkedHashMap<ShardId, ShardRouting> shards; // LinkedHashMap to preserve order
+    private final BucketedShards shards;
 
     private final LinkedHashSet<ShardRouting> initializingShards;
 
@@ -67,44 +142,43 @@ public class RoutingNode implements Iterable<ShardRouting> {
 
     private final HashMap<Index, LinkedHashSet<ShardRouting>> shardsByIndex;
 
-    public RoutingNode(String nodeId, DiscoveryNode node, ShardRouting... shards) {
-        this(nodeId, node, buildShardRoutingMap(shards));
-    }
-
-    RoutingNode(String nodeId, DiscoveryNode node, LinkedHashMap<ShardId, ShardRouting> shards) {
+    public RoutingNode(String nodeId, DiscoveryNode node, ShardRouting... shardRoutings) {
         this.nodeId = nodeId;
         this.node = node;
-        this.shards = shards;
+        final LinkedHashMap<ShardId, ShardRouting> primaryShards = new LinkedHashMap<>();
+        final LinkedHashMap<ShardId, ShardRouting> replicaShards = new LinkedHashMap<>();
+        this.shards = new BucketedShards(primaryShards, replicaShards);
         this.relocatingShards = new LinkedHashSet<>();
         this.initializingShards = new LinkedHashSet<>();
         this.shardsByIndex = new LinkedHashMap<>();
-        for (ShardRouting shardRouting : shards.values()) {
+
+        for (ShardRouting shardRouting : shardRoutings) {
             if (shardRouting.initializing()) {
                 initializingShards.add(shardRouting);
             } else if (shardRouting.relocating()) {
                 relocatingShards.add(shardRouting);
             }
             shardsByIndex.computeIfAbsent(shardRouting.index(), k -> new LinkedHashSet<>()).add(shardRouting);
-        }
-        assert invariant();
-    }
 
-    private static LinkedHashMap<ShardId, ShardRouting> buildShardRoutingMap(ShardRouting... shardRoutings) {
-        final LinkedHashMap<ShardId, ShardRouting> shards = new LinkedHashMap<>();
-        for (ShardRouting shardRouting : shardRoutings) {
-            ShardRouting previousValue = shards.put(shardRouting.shardId(), shardRouting);
+            ShardRouting previousValue;
+            if (shardRouting.primary()) {
+	        previousValue = primaryShards.put(shardRouting.shardId(), shardRouting);
+            } else {
+	        previousValue = replicaShards.put(shardRouting.shardId(), shardRouting);
+            }
+
             if (previousValue != null) {
-                throw new IllegalArgumentException(
-                    "Cannot have two different shards with same shard id " + shardRouting.shardId() + " on same node "
-                );
+	        throw new IllegalArgumentException("Cannot have two different shards with same shard id " + shardRouting.shardId() +
+	            " on same node ");
             }
         }
-        return shards;
+
+        assert invariant();
     }
 
     @Override
     public Iterator<ShardRouting> iterator() {
-        return Collections.unmodifiableCollection(shards.values()).iterator();
+        return shards.iterator();
     }
 
     /**
@@ -139,7 +213,7 @@ public int size() {
      */
     void add(ShardRouting shard) {
         assert invariant();
-        if (shards.containsKey(shard.shardId())) {
+        if (shards.add(shard) != null) {
             throw new IllegalStateException(
                 "Trying to add a shard "
                     + shard.shardId()
@@ -152,7 +226,6 @@ void add(ShardRouting shard) {
                     + "]"
             );
         }
-        shards.put(shard.shardId(), shard);
 
         if (shard.initializing()) {
             initializingShards.add(shard);
@@ -322,7 +395,7 @@ public int numberOfOwningShardsForIndex(final Index index) {
     public String prettyPrint() {
         StringBuilder sb = new StringBuilder();
         sb.append("-----node_id[").append(nodeId).append("][").append(node == null ? "X" : "V").append("]\n");
-        for (ShardRouting entry : shards.values()) {
+        for (ShardRouting entry : shards) {
             sb.append("--------").append(entry.shortSummary()).append('\n');
         }
         return sb.toString();
@@ -345,7 +418,9 @@ public String toString() {
     }
 
     public List<ShardRouting> copyShards() {
-        return new ArrayList<>(shards.values());
+        List<ShardRouting> result = new ArrayList<>();
+        shards.forEach(result::add);
+        return result;
     }
 
     public boolean isEmpty() {
@@ -355,23 +430,23 @@ public boolean isEmpty() {
     private boolean invariant() {
 
         // initializingShards must consistent with that in shards
-        Collection<ShardRouting> shardRoutingsInitializing = shards.values()
-            .stream()
+        Collection<ShardRouting> shardRoutingsInitializing = StreamSupport
+            .stream(shards.spliterator(), false)
             .filter(ShardRouting::initializing)
             .collect(Collectors.toList());
         assert initializingShards.size() == shardRoutingsInitializing.size();
         assert initializingShards.containsAll(shardRoutingsInitializing);
 
         // relocatingShards must consistent with that in shards
-        Collection<ShardRouting> shardRoutingsRelocating = shards.values()
-            .stream()
+        Collection<ShardRouting> shardRoutingsRelocating = StreamSupport
+            .stream(shards.spliterator(), false)
             .filter(ShardRouting::relocating)
             .collect(Collectors.toList());
         assert relocatingShards.size() == shardRoutingsRelocating.size();
         assert relocatingShards.containsAll(shardRoutingsRelocating);
 
-        final Map<Index, Set<ShardRouting>> shardRoutingsByIndex = shards.values()
-            .stream()
+        final Map<Index, Set<ShardRouting>> shardRoutingsByIndex = StreamSupport
+            .stream(shards.spliterator(), false)
             .collect(Collectors.groupingBy(ShardRouting::index, Collectors.toSet()));
         assert shardRoutingsByIndex.equals(shardsByIndex);
 
diff --git a/server/src/main/java/org/opensearch/cluster/routing/RoutingNodes.java b/server/src/main/java/org/opensearch/cluster/routing/RoutingNodes.java
index bf79ba26d527a..de51d579713e1 100644
--- a/server/src/main/java/org/opensearch/cluster/routing/RoutingNodes.java
+++ b/server/src/main/java/org/opensearch/cluster/routing/RoutingNodes.java
@@ -1284,6 +1284,8 @@ public Iterator<ShardRouting> nodeInterleavedShardIterator() {
             queue.add(entry.getValue().copyShards().iterator());
         }
         return new Iterator<ShardRouting>() {
+            private Queue<ShardRouting> replicaShards = new ArrayDeque<>();
+            private Queue<Iterator<ShardRouting>> replicaIterators = new ArrayDeque<>();
             public boolean hasNext() {
                 while (!queue.isEmpty()) {
                     if (queue.peek().hasNext()) {
@@ -1291,6 +1293,15 @@ public boolean hasNext() {
                     }
                     queue.poll();
                 }
+                if (!replicaShards.isEmpty()) {
+                    return true;
+                }
+                while (!replicaIterators.isEmpty()) {
+                    if (replicaIterators.peek().hasNext()) {
+                        return true;
+                    }
+                    replicaIterators.poll();
+                }
                 return false;
             }
 
@@ -1298,10 +1309,25 @@ public ShardRouting next() {
                 if (hasNext() == false) {
                     throw new NoSuchElementException();
                 }
-                Iterator<ShardRouting> iter = queue.poll();
-                ShardRouting result = iter.next();
-                queue.offer(iter);
-                return result;
+                while (!queue.isEmpty()) {
+                    Iterator<ShardRouting> iter = queue.poll();
+                    if (iter.hasNext()) {
+                        ShardRouting result = iter.next();
+                        if (result.primary()) {
+                            queue.offer(iter);
+                            return result;
+                        }
+                        replicaShards.offer(result);
+                        replicaIterators.offer(iter);
+                    }
+                }
+                if (!replicaShards.isEmpty()) {
+                    return replicaShards.poll();
+                }
+                Iterator<ShardRouting> replicaIterator = replicaIterators.poll();
+                ShardRouting replicaShard = replicaIterator.next();
+                replicaIterators.offer(replicaIterator);
+                return replicaShard;
             }
 
             public void remove() {