Added support for feature flags in opensearch.yml (#4959)

This change introduces a static store "settings"
in FeatureFlags.java file to enable isEnabled method to
fetch flag settings defined in opensearch.yml.

Signed-off-by: Nagaraj Tantri <nagarajtantri@gmail.com>

(cherry picked from commit 241bd42)

CHANGELOG.md

@@ -17,6 +17,8 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Support for labels on version bump PRs, skip label support for changelog verifier ([#4391](https://github.com/opensearch-project/OpenSearch/pull/4391))
 - Add a new node role 'search' which is dedicated to provide search capability ([#4689](https://github.com/opensearch-project/OpenSearch/pull/4689))
 - Introduce experimental searchable snapshot API ([#4680](https://github.com/opensearch-project/OpenSearch/pull/4680))
+- Added support for feature flags in opensearch.yml ([#4959](https://github.com/opensearch-project/OpenSearch/pull/4959))
+
 ### Dependencies
 - Bumps `com.diffplug.spotless` from 6.9.1 to 6.10.0
 - Bumps `xmlbeans` from 5.1.0 to 5.1.1

distribution/src/config/opensearch.yml

@@ -86,3 +86,26 @@ ${path.logs}
 # Require explicit names when deleting indices:
 #
 #action.destructive_requires_name: true
+#
+# ---------------------------------- Experimental Features -----------------------------------
+#
+# Gates the visibility of the index setting that allows changing of replication type.
+# Once the feature is ready for production release, this feature flag can be removed.
+#
+#opensearch.experimental.feature.replication_type.enabled: false
+#
+#
+# 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.
+#
+#opensearch.experimental.feature.remote_store.enabled: false
+#
+#
+# Gates the functionality of a new parameter to the snapshot restore API
+# that allows for creation of a new index type that searches a snapshot
+# directly in a remote repository without restoring all index data to disk
+# ahead of time.
+#
+#opensearch.experimental.feature.searchable_snapshot.enabled: false
+#
+#

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

@@ -0,0 +1,44 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.common.settings;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+import org.opensearch.common.settings.Setting.Property;
+import org.opensearch.common.util.FeatureFlags;
+
+/**
+ * Encapsulates all valid feature flag level settings.
+ *
+ * @opensearch.internal
+ */
+public class FeatureFlagSettings extends AbstractScopedSettings {
+
+    protected FeatureFlagSettings(
+        Settings settings,
+        Set<Setting<?>> settingsSet,
+        Set<SettingUpgrader<?>> settingUpgraders,
+        Property scope
+    ) {
+        super(settings, settingsSet, settingUpgraders, scope);
+    }
+
+    public static final Set<Setting<?>> BUILT_IN_FEATURE_FLAGS = Collections.unmodifiableSet(
+        new HashSet<>(
+            Arrays.asList(
+                FeatureFlags.REPLICATION_TYPE_SETTING,
+                FeatureFlags.REMOTE_STORE_SETTING,
+                FeatureFlags.SEARCHABLE_SNAPSHOT_SETTING,
+                FeatureFlags.EXTENSIONS_SETTING
+            )
+        )
+    );
+}

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

@@ -87,6 +87,9 @@ public SettingsModule(
         for (Setting<?> setting : IndexScopedSettings.BUILT_IN_INDEX_SETTINGS) {
             registerSetting(setting);
         }
+        for (Setting<?> setting : FeatureFlagSettings.BUILT_IN_FEATURE_FLAGS) {
+            registerSetting(setting);
+        }
 
         for (Map.Entry<String, List<Setting>> featureFlaggedSetting : IndexScopedSettings.FEATURE_FLAGGED_INDEX_SETTINGS.entrySet()) {
             if (FeatureFlags.isEnabled(featureFlaggedSetting.getKey())) {

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

@@ -8,6 +8,10 @@
 
 package org.opensearch.common.util;
 
+import org.opensearch.common.settings.Setting;
+import org.opensearch.common.settings.Setting.Property;
+import org.opensearch.common.settings.Settings;
+
 /**
  * Utility class to manage feature flags. Feature flags are system properties that must be set on the JVM.
  * These are used to gate the visibility/availability of incomplete features. Fore more information, see
@@ -37,12 +41,45 @@ public class FeatureFlags {
      */
     public static final String SEARCHABLE_SNAPSHOT = "opensearch.experimental.feature.searchable_snapshot.enabled";
 
+    /**
+     * Gates the functionality of extensions.
+     * Once the feature is ready for production release, this feature flag can be removed.
+     */
+    public static final String EXTENSIONS = "opensearch.experimental.feature.extensions.enabled";
+
+    /**
+     * Should store the settings from opensearch.yml.
+     */
+    private static Settings settings;
+
+    /**
+     * This method is responsible to map settings from opensearch.yml to local stored
+     * settings value. That is used for the existing isEnabled method.
+     *
+     * @param openSearchSettings The settings stored in opensearch.yml.
+     */
+    public static void initializeFeatureFlags(Settings openSearchSettings) {
+        settings = openSearchSettings;
+    }
+
     /**
      * Used to test feature flags whose values are expected to be booleans.
      * This method returns true if the value is "true" (case-insensitive),
      * and false otherwise.
      */
     public static boolean isEnabled(String featureFlagName) {
-        return "true".equalsIgnoreCase(System.getProperty(featureFlagName));
+        if ("true".equalsIgnoreCase(System.getProperty(featureFlagName))) {
+            // TODO: Remove the if condition once FeatureFlags are only supported via opensearch.yml
+            return true;
+        }
+        return settings != null && settings.getAsBoolean(featureFlagName, false);
     }
+
+    public static final Setting<Boolean> REPLICATION_TYPE_SETTING = Setting.boolSetting(REPLICATION_TYPE, false, Property.NodeScope);
+
+    public static final Setting<Boolean> REMOTE_STORE_SETTING = Setting.boolSetting(REMOTE_STORE, false, Property.NodeScope);
+
+    public static final Setting<Boolean> SEARCHABLE_SNAPSHOT_SETTING = Setting.boolSetting(SEARCHABLE_SNAPSHOT, false, Property.NodeScope);
+
+    public static final Setting<Boolean> EXTENSIONS_SETTING = Setting.boolSetting(EXTENSIONS, false, Property.NodeScope);
 }

server/src/main/java/org/opensearch/node/Node.java

@@ -424,6 +424,9 @@ protected Node(
             );
             final Settings settings = pluginsService.updatedSettings();
 
+            // Ensure to initialize Feature Flags via the settings from opensearch.yml
+            FeatureFlags.initializeFeatureFlags(settings);
+
             final Set<DiscoveryNodeRole> additionalRoles = pluginsService.filterPlugins(Plugin.class)
                 .stream()
                 .map(Plugin::getRoles)

test/framework/src/main/java/org/opensearch/test/OpenSearchIntegTestCase.java

@@ -106,6 +106,7 @@
 import org.opensearch.common.network.NetworkAddress;
 import org.opensearch.common.network.NetworkModule;
 import org.opensearch.common.regex.Regex;
+import org.opensearch.common.settings.FeatureFlagSettings;
 import org.opensearch.common.settings.Setting;
 import org.opensearch.common.settings.Setting.Property;
 import org.opensearch.common.settings.Settings;
@@ -769,6 +770,20 @@ public Settings indexSettings() {
         return builder.build();
     }
 
+    /**
+     * Setting all feature flag settings at base IT, which can be overridden later by individual
+     * IT classes.
+     *
+     * @return Feature flag settings.
+     */
+    protected Settings featureFlagSettings() {
+        Settings.Builder featureSettings = Settings.builder();
+        for (Setting builtInFlag : FeatureFlagSettings.BUILT_IN_FEATURE_FLAGS) {
+            featureSettings.put(builtInFlag.getKey(), builtInFlag.getDefaultRaw(Settings.EMPTY));
+        }
+        return featureSettings.build();
+    }
+
     /**
      * Creates one or more indices and asserts that the indices are acknowledged. If one of the indices
      * already exists this method will fail and wipe all the indices created so far.