Add auto_expand to index template settings

Signed-off-by: Chenyang Ji <cyji@amazon.com>

Author: ansjcy

src/main/java/org/opensearch/plugin/insights/core/exporter/LocalIndexExporter.java

@@ -64,8 +64,8 @@ public class LocalIndexExporter implements QueryInsightsExporter {
     private DateTimeFormatter indexPattern;
     private int deleteAfter;
     private final String id;
-    private static final int DEFAULT_NUMBER_OF_REPLICA = 0;
     private static final int DEFAULT_NUMBER_OF_SHARDS = 1;
+    private static final String DEFAULT_AUTO_EXPAND_REPLICAS = "0-2";
     private static final String TEMPLATE_NAME = "query_insights_top_queries_template";
     private long templatePriority;
 
@@ -179,7 +179,7 @@ void createIndexAndBulk(String indexName, List<SearchQueryRecord> records) throw
         createIndexRequest.settings(
             Settings.builder()
                 .put("index.number_of_shards", DEFAULT_NUMBER_OF_SHARDS)
-                .put("index.number_of_replicas", DEFAULT_NUMBER_OF_REPLICA)
+                .put("index.auto_expand_replicas", DEFAULT_AUTO_EXPAND_REPLICAS)
         );
         createIndexRequest.mapping(readIndexMappings());
 
@@ -378,7 +378,7 @@ void createTemplate(CompletableFuture<Boolean> future) {
             org.opensearch.cluster.metadata.Template template = new org.opensearch.cluster.metadata.Template(
                 Settings.builder()
                     .put("index.number_of_shards", DEFAULT_NUMBER_OF_SHARDS)
-                    .put("index.number_of_replicas", DEFAULT_NUMBER_OF_REPLICA)
+                    .put("index.auto_expand_replicas", DEFAULT_AUTO_EXPAND_REPLICAS)
                     .build(),
                 compressedMapping,
                 null

src/test/java/org/opensearch/plugin/insights/core/exporter/LocalIndexExporterTests.java

@@ -12,6 +12,7 @@
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.doAnswer;
+import static org.mockito.Mockito.doNothing;
 import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.doThrow;
 import static org.mockito.Mockito.mock;
@@ -26,13 +27,16 @@
 import java.time.ZoneOffset;
 import java.time.ZonedDateTime;
 import java.time.format.DateTimeFormatter;
+import java.util.Collections;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 import org.junit.Before;
+import org.mockito.ArgumentCaptor;
+import org.opensearch.action.admin.indices.create.CreateIndexRequest;
 import org.opensearch.action.admin.indices.exists.indices.IndicesExistsRequest;
 import org.opensearch.action.admin.indices.template.get.GetComposableIndexTemplateAction;
 import org.opensearch.action.admin.indices.template.put.PutComposableIndexTemplateAction;
@@ -371,4 +375,34 @@ public void testReadIndexMappingsWithEmptyMapping() throws IOException {
         LocalIndexExporter exporter = new LocalIndexExporter(client, clusterService, format, "", "id");
         assertEquals("{}", exporter.readIndexMappings());
     }
+
+    /**
+     * Test that createIndex correctly sets auto_expand_replicas
+     */
+    public void testCreateIndexWithAutoExpandReplicas() throws IOException {
+        LocalIndexExporter exporterSpy = spy(new LocalIndexExporter(client, clusterService, format, "{}", "id"));
+
+        ArgumentCaptor<CreateIndexRequest> requestCaptor = ArgumentCaptor.forClass(CreateIndexRequest.class);
+
+        // Mock the client.admin().indices().create() call
+        AdminClient adminClient = mock(AdminClient.class);
+        IndicesAdminClient indicesClient = mock(IndicesAdminClient.class);
+        when(client.admin()).thenReturn(adminClient);
+        when(adminClient.indices()).thenReturn(indicesClient);
+
+        doNothing().when(indicesClient).create(requestCaptor.capture(), any(ActionListener.class));
+        exporterSpy.createIndexAndBulk("test-index", Collections.emptyList());
+
+        // Verify the captured request
+        CreateIndexRequest capturedRequest = requestCaptor.getValue();
+        Settings settings = capturedRequest.settings();
+
+        // Verify the settings use auto_expand_replicas
+        assertEquals("test-index", capturedRequest.index());
+        assertEquals("0-2", settings.get("index.auto_expand_replicas"));
+        assertEquals("1", settings.get("index.number_of_shards"));
+
+        // Verify there is no number_of_replicas setting.
+        assertNull(settings.get("index.number_of_replicas"));
+    }
 }