Allow plugins to upgrade global custom metadata on startup

core/src/main/java/org/elasticsearch/cluster/metadata/MetaData.java

@@ -460,6 +460,11 @@ public IndexMetaData index(Index index) {
         return null;
     }
 
+    /** Returns true iff existing index has the same {@link IndexMetaData} instance */
+    public boolean hasIndexMetaData(final IndexMetaData indexMetaData) {
+        return indices.get(indexMetaData.getIndex().getName()) == indexMetaData;
+    }
+
     /**
      * Returns the {@link IndexMetaData} for this index.
      * @throws IndexNotFoundException if no metadata for this index is found

core/src/main/java/org/elasticsearch/gateway/GatewayMetaState.java

@@ -19,6 +19,7 @@
 
 package org.elasticsearch.gateway;
 
+import com.carrotsearch.hppc.cursors.ObjectObjectCursor;
 import org.elasticsearch.Version;
 import org.elasticsearch.cluster.ClusterChangedEvent;
 import org.elasticsearch.cluster.ClusterState;
@@ -37,14 +38,17 @@
 import org.elasticsearch.common.util.IndexFolderUpgrader;
 import org.elasticsearch.env.NodeEnvironment;
 import org.elasticsearch.index.Index;
+import org.elasticsearch.plugins.MetaDataUpgrader;
 
 import java.nio.file.DirectoryStream;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
 
 import static java.util.Collections.emptySet;
@@ -55,7 +59,6 @@ public class GatewayMetaState extends AbstractComponent implements ClusterStateL
     private final NodeEnvironment nodeEnv;
     private final MetaStateService metaStateService;
     private final DanglingIndicesState danglingIndicesState;
-    private final MetaDataIndexUpgradeService metaDataIndexUpgradeService;
 
     @Nullable
     private volatile MetaData previousMetaData;
@@ -65,12 +68,12 @@ public class GatewayMetaState extends AbstractComponent implements ClusterStateL
     @Inject
     public GatewayMetaState(Settings settings, NodeEnvironment nodeEnv, MetaStateService metaStateService,
                             DanglingIndicesState danglingIndicesState, TransportNodesListGatewayMetaState nodesListGatewayMetaState,
-                            MetaDataIndexUpgradeService metaDataIndexUpgradeService) throws Exception {
+                            MetaDataIndexUpgradeService metaDataIndexUpgradeService, MetaDataUpgrader metaDataUpgrader)
+        throws Exception {
         super(settings);
         this.nodeEnv = nodeEnv;
         this.metaStateService = metaStateService;
         this.danglingIndicesState = danglingIndicesState;
-        this.metaDataIndexUpgradeService = metaDataIndexUpgradeService;
         nodesListGatewayMetaState.init(this);
 
         if (DiscoveryNode.isDataNode(settings)) {
@@ -84,7 +87,21 @@ public GatewayMetaState(Settings settings, NodeEnvironment nodeEnv, MetaStateSer
             try {
                 ensureNoPre019State();
                 IndexFolderUpgrader.upgradeIndicesIfNeeded(settings, nodeEnv);
-                upgradeMetaData();
+                final MetaData metaData = metaStateService.loadFullState();
+                final MetaData upgradedMetaData = upgradeMetaData(metaData, metaDataIndexUpgradeService, metaDataUpgrader);
+                // We finished global state validation and successfully checked all indices for backward compatibility
+                // and found no non-upgradable indices, which means the upgrade can continue.
+                // Now it's safe to overwrite global and index metadata.
+                if (metaData != upgradedMetaData) {
+                    if (MetaData.isGlobalStateEquals(metaData, upgradedMetaData) == false) {
+                        metaStateService.writeGlobalState("upgrade", upgradedMetaData);
+                    }
+                    for (IndexMetaData indexMetaData : upgradedMetaData) {
+                        if (metaData.hasIndexMetaData(indexMetaData) == false) {
+                            metaStateService.writeIndex("upgrade", indexMetaData);
+                        }
+                    }
+                }
                 long startNS = System.nanoTime();
                 metaStateService.loadFullState();
                 logger.debug("took {} to load state", TimeValue.timeValueMillis(TimeValue.nsecToMSec(System.nanoTime() - startNS)));
@@ -216,24 +233,37 @@ private void ensureNoPre019State() throws Exception {
     /**
      * Elasticsearch 2.0 removed several deprecated features and as well as support for Lucene 3.x. This method calls
      * {@link MetaDataIndexUpgradeService} to makes sure that indices are compatible with the current version. The
-     * MetaDataIndexUpgradeService might also update obsolete settings if needed. When this happens we rewrite
-     * index metadata with new settings.
+     * MetaDataIndexUpgradeService might also update obsolete settings if needed.
+     * Allows upgrading global custom meta data via {@link MetaDataUpgrader#customMetaDataUpgraders}
+     *
+     * @return input <code>metaData</code> if no upgrade is needed or an upgraded metaData
      */
-    private void upgradeMetaData() throws Exception {
-        MetaData metaData = loadMetaState();
-        List<IndexMetaData> updateIndexMetaData = new ArrayList<>();
+    static MetaData upgradeMetaData(MetaData metaData,
+                                    MetaDataIndexUpgradeService metaDataIndexUpgradeService,
+                                    MetaDataUpgrader metaDataUpgrader) throws Exception {
+        // upgrade index meta data
+        boolean changed = false;
+        final MetaData.Builder upgradedMetaData = MetaData.builder(metaData);
         for (IndexMetaData indexMetaData : metaData) {
             IndexMetaData newMetaData = metaDataIndexUpgradeService.upgradeIndexMetaData(indexMetaData);
-            if (indexMetaData != newMetaData) {
-                updateIndexMetaData.add(newMetaData);
-            }
+            changed |= indexMetaData != newMetaData;
+            upgradedMetaData.put(newMetaData, false);
         }
-        // We successfully checked all indices for backward compatibility and found no non-upgradable indices, which
-        // means the upgrade can continue. Now it's safe to overwrite index metadata with the new version.
-        for (IndexMetaData indexMetaData : updateIndexMetaData) {
-            // since we upgraded the index folders already, write index state in the upgraded index folder
-            metaStateService.writeIndex("upgrade", indexMetaData);
+        // collect current customs
+        Map<String, MetaData.Custom> existingCustoms = new HashMap<>();
+        for (ObjectObjectCursor<String, MetaData.Custom> customCursor : metaData.customs()) {
+            existingCustoms.put(customCursor.key, customCursor.value);
+        }
+        // upgrade global custom meta data
+        Map<String, MetaData.Custom> upgradedCustoms = metaDataUpgrader.customMetaDataUpgraders.apply(existingCustoms);
+        if (upgradedCustoms.equals(existingCustoms) == false) {
+            existingCustoms.keySet().forEach(upgradedMetaData::removeCustom);
+            for (Map.Entry<String, MetaData.Custom> upgradedCustomEntry : upgradedCustoms.entrySet()) {
+                upgradedMetaData.putCustom(upgradedCustomEntry.getKey(), upgradedCustomEntry.getValue());
+            }
+            changed = true;
         }
+        return changed ? upgradedMetaData.build() : metaData;
     }
 
     // shard state BWC

core/src/main/java/org/elasticsearch/node/Node.java

@@ -36,6 +36,7 @@
 import org.elasticsearch.cluster.MasterNodeChangePredicate;
 import org.elasticsearch.cluster.NodeConnectionsService;
 import org.elasticsearch.cluster.action.index.MappingUpdatedAction;
+import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.routing.RoutingService;
 import org.elasticsearch.cluster.routing.allocation.AllocationService;
@@ -96,6 +97,7 @@
 import org.elasticsearch.plugins.IngestPlugin;
 import org.elasticsearch.plugins.MapperPlugin;
 import org.elasticsearch.plugins.Plugin;
+import org.elasticsearch.plugins.MetaDataUpgrader;
 import org.elasticsearch.plugins.PluginsService;
 import org.elasticsearch.plugins.RepositoryPlugin;
 import org.elasticsearch.plugins.ScriptPlugin;
@@ -134,6 +136,7 @@
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Function;
+import java.util.function.UnaryOperator;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
@@ -349,6 +352,11 @@ protected Node(final Environment environment, Collection<Class<? extends Plugin>
                 .flatMap(p -> p.createComponents(client, clusterService, threadPool, resourceWatcherService,
                                                  scriptModule.getScriptService(), searchModule.getSearchRequestParsers()).stream())
                 .collect(Collectors.toList());
+            Collection<UnaryOperator<Map<String, MetaData.Custom>>> customMetaDataUpgraders =
+                pluginsService.filterPlugins(Plugin.class).stream()
+                .map(Plugin::getCustomMetaDataUpgrader)
+                .collect(Collectors.toList());
+            final MetaDataUpgrader metaDataUpgrader = new MetaDataUpgrader(customMetaDataUpgraders);
             modules.add(b -> {
                     b.bind(PluginsService.class).toInstance(pluginsService);
                     b.bind(Client.class).toInstance(client);
@@ -371,6 +379,7 @@ protected Node(final Environment environment, Collection<Class<? extends Plugin>
                         b.bind(SearchService.class).to(searchServiceImpl).asEagerSingleton();
                     }
                     pluginComponents.stream().forEach(p -> b.bind((Class) p.getClass()).toInstance(p));
+                    b.bind(MetaDataUpgrader.class).toInstance(metaDataUpgrader);
                 }
             );
             injector = modules.createInjector();

core/src/main/java/org/elasticsearch/plugins/MetaDataUpgrader.java

@@ -0,0 +1,44 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.plugins;
+
+import org.elasticsearch.cluster.metadata.MetaData;
+
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.function.UnaryOperator;
+
+/**
+ * Upgrades {@link MetaData} on startup on behalf of installed {@link Plugin}s
+ */
+public class MetaDataUpgrader {
+    public final UnaryOperator<Map<String, MetaData.Custom>> customMetaDataUpgraders;
+
+    public MetaDataUpgrader(Collection<UnaryOperator<Map<String, MetaData.Custom>>> customMetaDataUpgraders) {
+        this.customMetaDataUpgraders = customs -> {
+            Map<String, MetaData.Custom> upgradedCustoms = new HashMap<>(customs);
+            for (UnaryOperator<Map<String, MetaData.Custom>> customMetaDataUpgrader : customMetaDataUpgraders) {
+                upgradedCustoms = customMetaDataUpgrader.apply(upgradedCustoms);
+            }
+            return upgradedCustoms;
+        };
+    }
+}

core/src/main/java/org/elasticsearch/plugins/Plugin.java

@@ -25,6 +25,7 @@
 
 import org.elasticsearch.action.ActionModule;
 import org.elasticsearch.client.Client;
+import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.component.LifecycleComponent;
 import org.elasticsearch.common.inject.Module;
@@ -43,6 +44,9 @@
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.watcher.ResourceWatcherService;
 
+import java.util.Map;
+import java.util.function.UnaryOperator;
+
 /**
  * An extension point allowing to plug in custom functionality.
  * <p>
@@ -124,6 +128,18 @@ public void onIndexModule(IndexModule indexModule) {}
      */
     public List<String> getSettingsFilter() { return Collections.emptyList(); }
 
+    /**
+     * Provides a function to modify global custom meta data on startup.
+     * <p>
+     * Plugins should return the input custom map via {@link UnaryOperator#identity()} if no upgrade is required.
+     * @return Never {@code null}. The same or upgraded {@code MetaData.Custom} map.
+     * @throws IllegalStateException if the node should not start because at least one {@code MetaData.Custom}
+     *         is unsupported
+     */
+    public UnaryOperator<Map<String, MetaData.Custom>> getCustomMetaDataUpgrader() {
+        return UnaryOperator.identity();
+    }
+
     /**
      * Old-style guice index level extension point.
      *