Ensure index templates are not applied to system indices

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

@@ -434,15 +434,21 @@ public ClusterState applyCreateIndexRequest(
             // in which case templates don't apply, so create the index from the source metadata
             return applyCreateIndexRequestWithExistingMetadata(currentState, request, silent, sourceMetadata, metadataTransformer);
         } else {
+            // The backing index may have a different name or prefix than the data stream name.
+            final String name = request.dataStreamName() != null ? request.dataStreamName() : request.index();
+
+            // Do not apply any templates to system indices
+            if (systemIndices.isSystemIndex(name)) {
+                return applyCreateIndexRequestWithNoTemplates(currentState, request, silent, metadataTransformer);
+            }
+
             // Hidden indices apply templates slightly differently (ignoring wildcard '*'
             // templates), so we need to check to see if the request is creating a hidden index
             // prior to resolving which templates it matches
             final Boolean isHiddenFromRequest = IndexMetadata.INDEX_HIDDEN_SETTING.exists(request.settings())
                 ? IndexMetadata.INDEX_HIDDEN_SETTING.get(request.settings())
                 : null;
 
-            // The backing index may have a different name or prefix than the data stream name.
-            final String name = request.dataStreamName() != null ? request.dataStreamName() : request.index();
             // Check to see if a v2 template matched
             final String v2Template = MetadataIndexTemplateService.findV2Template(
                 currentState.metadata(),
@@ -681,6 +687,17 @@ public void addRemoteStoreCustomMetadata(IndexMetadata.Builder tmpImdBuilder, bo
         tmpImdBuilder.putCustom(IndexMetadata.REMOTE_STORE_CUSTOM_KEY, remoteCustomData);
     }
 
+    public ClusterState applyCreateIndexRequestWithNoTemplates(
+        final ClusterState currentState,
+        final CreateIndexClusterStateUpdateRequest request,
+        final boolean silent,
+        final BiConsumer<Metadata.Builder, IndexMetadata> metadataTransformer
+    ) throws Exception {
+        // Using applyCreateIndexRequestWithV1Templates with empty list instead of applyCreateIndexRequestWithV2Template
+        // with null template as applyCreateIndexRequestWithV2Template has assertions when template is null
+        return applyCreateIndexRequestWithV1Templates(currentState, request, silent, Collections.emptyList(), metadataTransformer);
+    }
+
     private ClusterState applyCreateIndexRequestWithV1Templates(
         final ClusterState currentState,
         final CreateIndexClusterStateUpdateRequest request,