Add optional support for registering ClusterSettings update consumers

Author: JeremyDahlgren

server/src/main/java/org/elasticsearch/transport/ClusterSettingsLinkedProjectConfigService.java

@@ -15,6 +15,7 @@
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.core.FixForMultiProject;
+import org.elasticsearch.core.Nullable;
 
 import java.util.Collection;
 import java.util.List;
@@ -27,27 +28,40 @@ public class ClusterSettingsLinkedProjectConfigService extends AbstractLinkedPro
     private final Settings settings;
     private final ProjectResolver projectResolver;
 
+    /**
+     * Constructs a new {@link ClusterSettingsLinkedProjectConfigService}.
+     *
+     * @param settings        The initial node settings available on startup, used in {@link #getInitialLinkedProjectConfigs()}.
+     * @param clusterSettings The {@link ClusterSettings} to add setting update consumers to, if non-null.
+     * @param projectResolver The {@link ProjectResolver} to use to resolve the origin project ID.
+     */
     @SuppressWarnings("this-escape")
-    public ClusterSettingsLinkedProjectConfigService(Settings settings, ClusterSettings clusterSettings, ProjectResolver projectResolver) {
+    public ClusterSettingsLinkedProjectConfigService(
+        Settings settings,
+        @Nullable ClusterSettings clusterSettings,
+        ProjectResolver projectResolver
+    ) {
         this.settings = settings;
         this.projectResolver = projectResolver;
-        List<Setting.AffixSetting<?>> remoteClusterSettings = List.of(
-            RemoteClusterSettings.REMOTE_CLUSTER_COMPRESS,
-            RemoteClusterSettings.REMOTE_CLUSTER_PING_SCHEDULE,
-            RemoteClusterSettings.REMOTE_CONNECTION_MODE,
-            RemoteClusterSettings.SniffConnectionStrategySettings.REMOTE_CLUSTERS_PROXY,
-            RemoteClusterSettings.SniffConnectionStrategySettings.REMOTE_CLUSTER_SEEDS,
-            RemoteClusterSettings.SniffConnectionStrategySettings.REMOTE_NODE_CONNECTIONS,
-            RemoteClusterSettings.ProxyConnectionStrategySettings.PROXY_ADDRESS,
-            RemoteClusterSettings.ProxyConnectionStrategySettings.REMOTE_SOCKET_CONNECTIONS,
-            RemoteClusterSettings.ProxyConnectionStrategySettings.SERVER_NAME
-        );
-        clusterSettings.addAffixGroupUpdateConsumer(remoteClusterSettings, this::settingsChangedCallback);
-        clusterSettings.addAffixUpdateConsumer(
-            RemoteClusterSettings.REMOTE_CLUSTER_SKIP_UNAVAILABLE,
-            this::skipUnavailableChangedCallback,
-            (alias, value) -> {}
-        );
+        if (clusterSettings != null) {
+            List<Setting.AffixSetting<?>> remoteClusterSettings = List.of(
+                RemoteClusterSettings.REMOTE_CLUSTER_COMPRESS,
+                RemoteClusterSettings.REMOTE_CLUSTER_PING_SCHEDULE,
+                RemoteClusterSettings.REMOTE_CONNECTION_MODE,
+                RemoteClusterSettings.SniffConnectionStrategySettings.REMOTE_CLUSTERS_PROXY,
+                RemoteClusterSettings.SniffConnectionStrategySettings.REMOTE_CLUSTER_SEEDS,
+                RemoteClusterSettings.SniffConnectionStrategySettings.REMOTE_NODE_CONNECTIONS,
+                RemoteClusterSettings.ProxyConnectionStrategySettings.PROXY_ADDRESS,
+                RemoteClusterSettings.ProxyConnectionStrategySettings.REMOTE_SOCKET_CONNECTIONS,
+                RemoteClusterSettings.ProxyConnectionStrategySettings.SERVER_NAME
+            );
+            clusterSettings.addAffixGroupUpdateConsumer(remoteClusterSettings, this::settingsChangedCallback);
+            clusterSettings.addAffixUpdateConsumer(
+                RemoteClusterSettings.REMOTE_CLUSTER_SKIP_UNAVAILABLE,
+                this::skipUnavailableChangedCallback,
+                (alias, value) -> {}
+            );
+        }
     }
 
     @Override
@@ -59,7 +73,6 @@ public Collection<LinkedProjectConfig> getInitialLinkedProjectConfigs() {
             .toList();
     }
 
-
     private void settingsChangedCallback(String clusterAlias, Settings newSettings) {
         final var mergedSettings = Settings.builder().put(settings, false).put(newSettings, false).build();
         @FixForMultiProject(description = "Refactor to add the linked project ID associated with the alias.")

server/src/main/java/org/elasticsearch/transport/TransportService.java

@@ -276,11 +276,7 @@ public TransportService(
             clusterSettings,
             connectionManager,
             taskManger,
-            new ClusterSettingsLinkedProjectConfigService(
-                settings,
-                clusterSettings != null ? clusterSettings : ClusterSettings.createBuiltInClusterSettings(),
-                DefaultProjectResolver.INSTANCE
-            ),
+            new ClusterSettingsLinkedProjectConfigService(settings, clusterSettings, DefaultProjectResolver.INSTANCE),
             DefaultProjectResolver.INSTANCE
         );
     }
@@ -317,11 +313,11 @@ public TransportService(
         if (clusterSettings != null) {
             clusterSettings.addSettingsUpdateConsumer(TransportSettings.TRACE_LOG_INCLUDE_SETTING, this::setTracerLogInclude);
             clusterSettings.addSettingsUpdateConsumer(TransportSettings.TRACE_LOG_EXCLUDE_SETTING, this::setTracerLogExclude);
-            if (remoteClusterClient) {
-                linkedProjectConfigService.register(remoteClusterService);
-            }
             clusterSettings.addSettingsUpdateConsumer(TransportSettings.SLOW_OPERATION_THRESHOLD_SETTING, transport::setSlowLogThreshold);
         }
+        if (remoteClusterClient) {
+            linkedProjectConfigService.register(remoteClusterService);
+        }
         registerRequestHandler(
             HANDSHAKE_ACTION_NAME,
             EsExecutors.DIRECT_EXECUTOR_SERVICE,