Removing feature flags for tiered storage settings (#20996)

* Removing feature flags for tiered storage settings

Signed-off-by: Shubh Sahu <shubhvs@amazon.com>

* Updating the IT

Signed-off-by: Shubh Sahu <shubhvs@amazon.com>

---------

Signed-off-by: Shubh Sahu <shubhvs@amazon.com>
Co-authored-by: Shubh Sahu <shubhvs@amazon.com>

Author: astute-decipher

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

@@ -22,7 +22,6 @@
 import org.opensearch.action.search.SearchResponse;
 import org.opensearch.cluster.metadata.IndexMetadata;
 import org.opensearch.common.settings.Settings;
-import org.opensearch.common.settings.SettingsException;
 import org.opensearch.common.util.FeatureFlags;
 import org.opensearch.core.common.unit.ByteSizeUnit;
 import org.opensearch.core.common.unit.ByteSizeValue;
@@ -89,7 +88,7 @@ protected Settings nodeSettings(int nodeOrdinal) {
             .build();
     }
 
-    public void testWritableWarmFeatureFlagDisabled() {
+    public void testWritableWarmSettingAcceptedWhenFeatureFlagDisabled() {
         Settings clusterSettings = Settings.builder()
             .put(super.nodeSettings(0))
             .put(FeatureFlags.WRITABLE_WARM_INDEX_EXPERIMENTAL_FLAG, false)
@@ -105,18 +104,9 @@ public void testWritableWarmFeatureFlagDisabled() {
             .put(IndexModule.IS_WARM_INDEX_SETTING.getKey(), false)
             .build();
 
-        try {
-            prepareCreate(INDEX_NAME).setSettings(indexSettings).get();
-            fail("Should have thrown Exception as setting should not be registered if Feature Flag is Disabled");
-        } catch (SettingsException ex) {
-            assertEquals(
-                "unknown setting ["
-                    + IndexModule.IS_WARM_INDEX_SETTING.getKey()
-                    + "] please check that any required plugins are installed, or check the "
-                    + "breaking changes documentation for removed settings",
-                ex.getMessage()
-            );
-        }
+        // Setting is now always registered (built-in), so index creation should succeed
+        // even when the feature flag is disabled
+        assertAcked(prepareCreate(INDEX_NAME).setSettings(indexSettings).get());
     }
 
     public void testWritableWarmBasic() throws Exception {

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

@@ -41,7 +41,6 @@
 import org.opensearch.common.annotation.PublicApi;
 import org.opensearch.common.logging.Loggers;
 import org.opensearch.common.settings.Setting.Property;
-import org.opensearch.common.util.FeatureFlags;
 import org.opensearch.index.IndexModule;
 import org.opensearch.index.IndexSettings;
 import org.opensearch.index.IndexSortConfig;
@@ -305,6 +304,12 @@ public final class IndexScopedSettings extends AbstractScopedSettings {
                 IndexSettings.INDEX_DERIVED_SOURCE_SETTING,
                 IndexSettings.INDEX_DERIVED_SOURCE_TRANSLOG_ENABLED_SETTING,
 
+                // Writable warm / tiering settings - always registered so nodes can parse
+                // index metadata even when the feature flag is disabled
+                IndexModule.INDEX_STORE_LOCALITY_SETTING,
+                IndexModule.INDEX_TIERING_STATE,
+                IndexModule.IS_WARM_INDEX_SETTING,
+
                 // validate that built-in similarities don't get redefined
                 Setting.groupSetting("index.similarity.", (s) -> {
                     Map<String, Settings> groups = s.getAsGroups();
@@ -327,11 +332,7 @@ public final class IndexScopedSettings extends AbstractScopedSettings {
      * is ready for production release, the feature flag can be removed, and the
      * setting should be moved to {@link #BUILT_IN_INDEX_SETTINGS}.
      */
-    public static final Map<String, List<Setting>> FEATURE_FLAGGED_INDEX_SETTINGS = Map.of(
-        FeatureFlags.WRITABLE_WARM_INDEX_EXPERIMENTAL_FLAG,
-        // TODO: Create a separate feature flag for hot tiering index state.
-        List.of(IndexModule.INDEX_STORE_LOCALITY_SETTING, IndexModule.INDEX_TIERING_STATE, IndexModule.IS_WARM_INDEX_SETTING)
-    );
+    public static final Map<String, List<Setting>> FEATURE_FLAGGED_INDEX_SETTINGS = Map.of();
 
     public static final IndexScopedSettings DEFAULT_SCOPED_SETTINGS = new IndexScopedSettings(Settings.EMPTY, BUILT_IN_INDEX_SETTINGS);