Added new Setting property UnmodifiableOnRestore to prevent updating settings on restore snapshot

CHANGELOG.md

@@ -88,6 +88,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Fix _list/shards API failing when closed indices are present ([#16606](https://github.com/opensearch-project/OpenSearch/pull/16606))
 - Fix remote shards balance ([#15335](https://github.com/opensearch-project/OpenSearch/pull/15335))
 - Always use `constant_score` query for `match_only_text` field ([#16964](https://github.com/opensearch-project/OpenSearch/pull/16964))
+- Fixing the bug to prevent updating the index.knn setting during restore snapshot ([#16957](https://github.com/opensearch-project/OpenSearch/pull/16957))
 
 ### Security
 

server/src/internalClusterTest/java/org/opensearch/remotestore/RemoteRestoreSnapshotIT.java

@@ -740,6 +740,23 @@ public void testInvalidRestoreRequestScenarios() throws Exception {
         );
         assertTrue(exception.getMessage().contains("cannot modify setting [index.remote_store.segment.repository]" + " on restore"));
 
+        // try index restore with index.knn setting modified
+        Settings indexKnnSettings = Settings.builder().put(IndexMetadata.SETTING_KNN_ENABLED, false).build();
+
+        exception = expectThrows(
+            SnapshotRestoreException.class,
+            () -> client().admin()
+                .cluster()
+                .prepareRestoreSnapshot(snapshotRepo, snapshotName1)
+                .setWaitForCompletion(false)
+                .setIndexSettings(indexKnnSettings)
+                .setIndices(index)
+                .setRenamePattern(index)
+                .setRenameReplacement(restoredIndex)
+                .get()
+        );
+        assertTrue(exception.getMessage().contains("cannot modify setting [index.knn]" + " on restore"));
+
         // try index restore with remote store repository and translog store repository disabled
         exception = expectThrows(
             SnapshotRestoreException.class,

server/src/main/java/org/opensearch/cluster/metadata/IndexMetadata.java

@@ -271,6 +271,8 @@ static Setting<Integer> buildNumberOfShardsSetting() {
         Property.IndexScope
     );
 
+    public static final String SETTING_KNN_ENABLED = "index.knn";
+
     public static final Setting<Integer> INDEX_NUMBER_OF_ROUTING_SHARDS_SETTING = Setting.intSetting(
         "index.number_of_routing_shards",
         INDEX_NUMBER_OF_SHARDS_SETTING,

server/src/main/java/org/opensearch/snapshots/RestoreService.java

@@ -120,6 +120,7 @@
 import static org.opensearch.cluster.metadata.IndexMetadata.SETTING_CREATION_DATE;
 import static org.opensearch.cluster.metadata.IndexMetadata.SETTING_HISTORY_UUID;
 import static org.opensearch.cluster.metadata.IndexMetadata.SETTING_INDEX_UUID;
+import static org.opensearch.cluster.metadata.IndexMetadata.SETTING_KNN_ENABLED;
 import static org.opensearch.cluster.metadata.IndexMetadata.SETTING_NUMBER_OF_REPLICAS;
 import static org.opensearch.cluster.metadata.IndexMetadata.SETTING_NUMBER_OF_SEARCH_REPLICAS;
 import static org.opensearch.cluster.metadata.IndexMetadata.SETTING_NUMBER_OF_SHARDS;
@@ -171,7 +172,8 @@ public class RestoreService implements ClusterStateApplier {
             SETTING_HISTORY_UUID,
             SETTING_REMOTE_STORE_ENABLED,
             SETTING_REMOTE_SEGMENT_STORE_REPOSITORY,
-            SETTING_REMOTE_TRANSLOG_STORE_REPOSITORY
+            SETTING_REMOTE_TRANSLOG_STORE_REPOSITORY,
+            SETTING_KNN_ENABLED
         )
     );