Add index level setting for remote store

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

@@ -283,6 +283,17 @@ public Iterator<Setting<?>> settings() {
         Property.Final
     );
 
+    public static final String SETTING_REMOTE_STORE = "index.remote_store";
+    /**
+     * Used to specify if the index data should be persisted in the remote store.
+     */
+    public static final Setting<Boolean> INDEX_REMOTE_STORE_SETTING = Setting.boolSetting(
+        SETTING_REMOTE_STORE,
+        false,
+        Property.IndexScope,
+        Property.Final
+    );
+
     public static final String SETTING_AUTO_EXPAND_REPLICAS = "index.auto_expand_replicas";
     public static final Setting<AutoExpandReplicas> INDEX_AUTO_EXPAND_REPLICAS_SETTING = AutoExpandReplicas.SETTING;
 

server/src/main/java/org/opensearch/common/settings/IndexScopedSettings.java

@@ -217,7 +217,9 @@ public final class IndexScopedSettings extends AbstractScopedSettings {
      */
     public static final Map<String, Setting> FEATURE_FLAGGED_INDEX_SETTINGS = Map.of(
         FeatureFlags.REPLICATION_TYPE,
-        IndexMetadata.INDEX_REPLICATION_TYPE_SETTING
+        IndexMetadata.INDEX_REPLICATION_TYPE_SETTING,
+        FeatureFlags.REMOTE_STORE,
+        IndexMetadata.INDEX_REMOTE_STORE_SETTING
     );
 
     public static final IndexScopedSettings DEFAULT_SCOPED_SETTINGS = new IndexScopedSettings(Settings.EMPTY, BUILT_IN_INDEX_SETTINGS);

server/src/main/java/org/opensearch/common/util/FeatureFlags.java

@@ -23,6 +23,12 @@ public class FeatureFlags {
      */
     public static final String REPLICATION_TYPE = "opensearch.experimental.feature.replication_type.enabled";
 
+    /**
+     * Gates the visibility of the index setting that allows persisting data to remote store along with local disk.
+     * Once the feature is ready for production release, this feature flag can be removed.
+     */
+    public static final String REMOTE_STORE = "opensearch.experimental.feature.remote_store.enabled";
+
     /**
      * Used to test feature flags whose values are expected to be booleans.
      * This method returns true if the value is "true" (case-insensitive),

server/src/main/java/org/opensearch/index/IndexSettings.java

@@ -534,6 +534,7 @@ public final class IndexSettings {
     private final Settings nodeSettings;
     private final int numberOfShards;
     private final ReplicationType replicationType;
+    private final boolean isRemoteStoreEnabled;
     // volatile fields are updated via #updateIndexMetadata(IndexMetadata) under lock
     private volatile Settings settings;
     private volatile IndexMetadata indexMetadata;
@@ -686,6 +687,7 @@ public IndexSettings(final IndexMetadata indexMetadata, final Settings nodeSetti
         this.indexMetadata = indexMetadata;
         numberOfShards = settings.getAsInt(IndexMetadata.SETTING_NUMBER_OF_SHARDS, null);
         replicationType = ReplicationType.parseString(settings.get(IndexMetadata.SETTING_REPLICATION_TYPE));
+        isRemoteStoreEnabled = settings.getAsBoolean(IndexMetadata.SETTING_REMOTE_STORE, false);
 
         this.searchThrottled = INDEX_SEARCH_THROTTLED.get(settings);
         this.queryStringLenient = QUERY_STRING_LENIENT_SETTING.get(settings);
@@ -927,6 +929,13 @@ public boolean isSegRepEnabled() {
         return ReplicationType.SEGMENT.equals(replicationType);
     }
 
+    /**
+     * Returns if remote store is enabled for this index.
+     */
+    public boolean isRemoteStoreEnabled() {
+        return isRemoteStoreEnabled;
+    }
+
     /**
      * Returns the node settings. The settings returned from {@link #getSettings()} are a merged version of the
      * index settings and the node settings where node settings are overwritten by index settings.

server/src/test/java/org/opensearch/common/util/FeatureFlagTests.java

@@ -21,6 +21,7 @@ public class FeatureFlagTests extends OpenSearchTestCase {
     @BeforeClass
     public static void enableFeature() {
         AccessController.doPrivileged((PrivilegedAction<String>) () -> System.setProperty(FeatureFlags.REPLICATION_TYPE, "true"));
+        AccessController.doPrivileged((PrivilegedAction<String>) () -> System.setProperty(FeatureFlags.REMOTE_STORE, "true"));
     }
 
     public void testReplicationTypeFeatureFlag() {
@@ -40,4 +41,10 @@ public void testNonBooleanFeatureFlag() {
         assertNotNull(System.getProperty(javaVersionProperty));
         assertFalse(FeatureFlags.isEnabled(javaVersionProperty));
     }
+
+    public void testRemoteStoreFeatureFlag() {
+        String remoteStoreFlag = FeatureFlags.REMOTE_STORE;
+        assertNotNull(System.getProperty(remoteStoreFlag));
+        assertTrue(FeatureFlags.isEnabled(remoteStoreFlag));
+    }
 }

server/src/test/java/org/opensearch/index/IndexSettingsTests.java

@@ -41,6 +41,7 @@
 import org.opensearch.common.settings.Settings;
 import org.opensearch.common.unit.ByteSizeValue;
 import org.opensearch.common.unit.TimeValue;
+import org.opensearch.common.util.FeatureFlags;
 import org.opensearch.index.translog.Translog;
 import org.opensearch.test.OpenSearchTestCase;
 import org.opensearch.test.VersionUtils;
@@ -56,6 +57,7 @@
 import static org.hamcrest.CoreMatchers.equalTo;
 import static org.hamcrest.core.StringContains.containsString;
 import static org.hamcrest.object.HasToString.hasToString;
+import static org.opensearch.common.settings.IndexScopedSettings.FEATURE_FLAGGED_INDEX_SETTINGS;
 
 public class IndexSettingsTests extends OpenSearchTestCase {
 
@@ -753,4 +755,41 @@ public void testIgnoreTranslogRetentionSettingsIfSoftDeletesEnabled() {
         assertThat(indexSettings.getTranslogRetentionAge().millis(), equalTo(-1L));
         assertThat(indexSettings.getTranslogRetentionSize().getBytes(), equalTo(-1L));
     }
+
+    public void testRemoteStoreDefaultSetting() {
+        IndexMetadata metadata = newIndexMeta(
+            "index",
+            Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT).build()
+        );
+        IndexSettings settings = new IndexSettings(metadata, Settings.EMPTY);
+        assertFalse(settings.isRemoteStoreEnabled());
+    }
+
+    public void testRemoteStoreExplicitSetting() {
+        IndexMetadata metadata = newIndexMeta(
+            "index",
+            Settings.builder()
+                .put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT)
+                .put(IndexMetadata.SETTING_REMOTE_STORE, true)
+                .build()
+        );
+        IndexSettings settings = new IndexSettings(metadata, Settings.EMPTY);
+        assertTrue(settings.isRemoteStoreEnabled());
+    }
+
+    public void testUpdateRemoteStoreFails() {
+        Set<Setting<?>> remoteStoreSettingSet = new HashSet<>();
+        remoteStoreSettingSet.add(FEATURE_FLAGGED_INDEX_SETTINGS.get(FeatureFlags.REMOTE_STORE));
+        IndexScopedSettings settings = new IndexScopedSettings(Settings.EMPTY, remoteStoreSettingSet);
+        IllegalArgumentException error = expectThrows(
+            IllegalArgumentException.class,
+            () -> settings.updateSettings(
+                Settings.builder().put("index.remote_store", randomBoolean()).build(),
+                Settings.builder(),
+                Settings.builder(),
+                "index"
+            )
+        );
+        assertEquals(error.getMessage(), "final index setting [index.remote_store], not updateable");
+    }
 }