Elasticsearch6.3.2啓動過程源碼閱讀記錄

Elasticsearch6.3.2啓動過程源碼閱讀記錄

網上有不少關於es的源碼分析，以爲本身技術深度還不夠，因此這些文章只是看源碼過程當中的一個筆記，談不上分析。

整個啓動過程以類名.方法名，按順序依次描述以下：

1. Elasticsearch.main啓動入口類，註冊JVM關閉鉤子用來清理資源。

2. Command.mainwithoutErrorHandling 在es正式啓動以前，加載一些命令：好比 ./elasticsearch -help命令

starts elasticsearch
   Option                Description                                               
   ------                -----------                                               
   -E <KeyValuePair>     Configure a setting                                       
   -V, --version         Prints elasticsearch version information and exits        
   -d, --daemonize       Starts Elasticsearch in the background                    
   -h, --help            show help

1. EnvironmentAwareCommand.execute加載配置參數

   putSystemPropertyIfSettingIsMissing(settings, "path.data", "es.path.data");
           putSystemPropertyIfSettingIsMissing(settings, "path.home", "es.path.home");
           putSystemPropertyIfSettingIsMissing(settings, "path.logs", "es.path.logs");

   ​

2. InternalSettingsPrepare.prePareEnvironment解析ElasticSearch.yml中的配置參數

   Prepares the settings by gathering all elasticsearch system properties, optionally loading the configuration settings,and then replacing all property placeholders.and then replacing all property placeholders.

1. ElasticSearch.execute執行初始化命令。另外在源碼中還有看到一些有趣的註釋，好比必須設置java.io.tmpdir，這個參數在 config/jvm.options文件中指定。

   // a misconfigured java.io.tmpdir can cause hard-to-diagnose problems later, so reject it immediately
           try {
               env.validateTmpFile();
           } catch (IOException e) {
               throw new UserException(ExitCodes.CONFIG, e.getMessage());
           }

   ​

2. Bootstrap.init正式開始啓動ElasticSearch。This method is invoked by {@link Elasticsearch#main(String[])} to startup elasticsearch。

   • 建立節點啓動時須要的環境變量參數

     final Environment environment = createEnvironment(foreground, pidFile, keystore, initialEnv.settings(), initialEnv.configFile());

   • checkLucene()檢查匹配的Lucene jar包。

   • 建立節點，在下面Node構造方法中將詳細分析這個過程。

     node = new Node(environment) {
                 @Override
                 protected void validateNodeBeforeAcceptingRequests(
                     final BootstrapContext context,
                     final BoundTransportAddress boundTransportAddress, List<BootstrapCheck> checks) throws NodeValidationException {
                     BootstrapChecks.check(context, boundTransportAddress, checks);
                 }
             };

     ​

1. Node.java 構造方法 Node(final Environment environment, Collection<Class<? extends Plugin>> classpathPlugins)。在這個構建方法裏面，完成了建立一個節點所需的各類信息，這個方法很是重要，下面就例舉出幾個節點建立過程當中幾個重要的流程：

   • 設置節點環境變量信息(A component that holds all data paths for a single node.)

   nodeEnvironment = new NodeEnvironment(tmpSettings, environment);

   ​

   • 構造插件服務(PluginService)，

     this.pluginsService = new PluginsService(tmpSettings, environment.configFile(), environment.modulesFile(), environment.pluginsFile(), classpathPlugins);

     看這個構造方法的註釋：

     /**
          * Constructs a new PluginService
          * @param settings The settings of the system
          * @param modulesDirectory The directory modules exist in, or null if modules should not be loaded from the filesystem
          * @param pluginsDirectory The directory plugins exist in, or null if plugins should not be loaded from the filesystem
          * @param classpathPlugins Plugins that exist in the classpath which should be loaded
          */
         public PluginsService(Settings settings, Path configPath, Path modulesDirectory, Path pluginsDirectory, Collection<Class<? extends Plugin>> classpathPlugins) {

     其實就是加載：elasticsearch-6.3.2/modules 和 elasticsearch-6.3.2/plugins兩個目錄下的內容。
     

     ​

   • 建立自定義的線程池，節點執行各類任務用的吧。

     final ThreadPool threadPool = new ThreadPool(settings, executorBuilders.toArray(new ExecutorBuilder[0]));

     ​

   • 建立NodeClient，Client that executes actions on the local node。

     client = new NodeClient(settings, threadPool);

     ​

   • AnalysisModule (An internal registry for tokenizer, token filter, char filter and analyzer)各類分詞器。

     AnalysisModule analysisModule = new AnalysisModule(this.environment, pluginsService.filterPlugins(AnalysisPlugin.class));

     ​

   • SettingsModule(A module that binds the provided settings to the {@link Settings} interface) 各類配置參數用到。好比 jvm.options 和 elasticsearch.yml裏面配置的各類參數。

     final SettingsModule settingsModule = new SettingsModule(this.settings, additionalSettings, additionalSettingsFilter);

     ​

   • 節點是集羣的一份子，確定須要集羣相關的服務

     final ClusterService clusterService = new ClusterService(settings, settingsModule.getClusterSettings(), threadPool,
                    ClusterModule.getClusterStateCustomSuppliers(clusterPlugins));

     ​

   • 集羣信息相關服務(Interface for a class used to gather information about a cluster at regular intervals) 週期性同步集羣狀態。

     final ClusterInfoService clusterInfoService = newClusterInfoService(settings, clusterService, threadPool, client, listener::onNewInfo);

     ​

   • 建立Module

     ModulesBuilder modules = new ModulesBuilder();
     // plugin modules must be added here, before others or we can get crazy injection errors...
                 for (Module pluginModule : pluginsService.createGuiceModules()) {
                     modules.add(pluginModule);
                 }

     好比：SearchModule(Sets up things that can be done at search time like queries, aggregations, and suggesters)

     SearchModule searchModule = new SearchModule(settings, false, pluginsService.filterPlugins(SearchPlugin.class));

     還有 ActionModule(Builds and binds the generic action map, all {@link TransportAction}s, and {@link ActionFilters}.)

     ActionModule actionModule = new ActionModule(false, settings, clusterModule.getIndexNameExpressionResolver(),
                     settingsModule.getIndexScopedSettings(), settingsModule.getClusterSettings(), settingsModule.getSettingsFilter(),
                     threadPool, pluginsService.filterPlugins(ActionPlugin.class), client, circuitBreakerService, usageService);
                 modules.add(actionModule);

     還有 DiscoveryModule(A module for loading classes for node discovery)

     final DiscoveryModule discoveryModule = new DiscoveryModule(this.settings, threadPool, transportService, namedWriteableRegistry,
                     networkService, clusterService.getMasterService(), clusterService.getClusterApplierService(),
                     clusterService.getClusterSettings(), pluginsService.filterPlugins(DiscoveryPlugin.class),
                     clusterModule.getAllocationService());

     看一下，一共都有哪些module:

     ​

     最終關聯了一大批的Module

     modules.add(b -> {
                         b.bind(Node.class).toInstance(this);
                         b.bind(NodeService.class).toInstance(nodeService);
                         b.bind(NamedXContentRegistry.class).toInstance(xContentRegistry);
                         b.bind(PluginsService.class).toInstance(pluginsService);
                         b.bind(Client.class).toInstance(client);
                         b.bind(NodeClient.class).toInstance(client);
                         b.bind(Environment.class).toInstance(this.environment);
                         b.bind(ThreadPool.class).toInstance(threadPool);
                         b.bind(NodeEnvironment.class).toInstance(nodeEnvironment);
                         b.bind(ResourceWatcherService.class).toInstance(resourceWatcherService);
                         b.bind(CircuitBreakerService.class).toInstance(circuitBreakerService);
                         b.bind(BigArrays.class).toInstance(bigArrays);
                         b.bind(ScriptService.class).toInstance(scriptModule.getScriptService());
                         b.bind(AnalysisRegistry.class).toInstance(analysisModule.getAnalysisRegistry());
                         b.bind(IngestService.class).toInstance(ingestService);
                         b.bind(UsageService.class).toInstance(usageService);
                         b.bind(NamedWriteableRegistry.class).toInstance(namedWriteableRegistry);
                         b.bind(MetaDataUpgrader.class).toInstance(metaDataUpgrader);
                         b.bind(MetaStateService.class).toInstance(metaStateService);
                         b.bind(IndicesService.class).toInstance(indicesService);
                         b.bind(SearchService.class).toInstance(searchService);
                         b.bind(SearchTransportService.class).toInstance(searchTransportService);
                         b.bind(SearchPhaseController.class).toInstance(new SearchPhaseController(settings,
                             searchService::createReduceContext));
                         b.bind(Transport.class).toInstance(transport);
                         b.bind(TransportService.class).toInstance(transportService);
                         b.bind(NetworkService.class).toInstance(networkService);
                         b.bind(UpdateHelper.class).toInstance(new UpdateHelper(settings, scriptModule.getScriptService()));
                         b.bind(MetaDataIndexUpgradeService.class).toInstance(metaDataIndexUpgradeService);
                         b.bind(ClusterInfoService.class).toInstance(clusterInfoService);
                         b.bind(GatewayMetaState.class).toInstance(gatewayMetaState);
                         b.bind(Discovery.class).toInstance(discoveryModule.getDiscovery());

   總之，Node.java的構造方法裏面實現了建立一個ElasticSearch節點所必須的各類信息，想要了解ElasticSearch節點的內部結構，應該就得多看看這個方法裏面的代碼吧。

2. ModulesBuilder.createInjector 使用了Guice 依賴注入。

   injector = modules.createInjector();

3. Node.start，前面建立了節點，如今開始啓動節點。(Start the node. If the node is already started, this method is no-op)

   • 先拿到對象實例，再啓動

     injector.getInstance(MappingUpdatedAction.class).setClient(client);
             injector.getInstance(IndicesService.class).start();
             injector.getInstance(IndicesClusterStateService.class).start();
             injector.getInstance(SnapshotsService.class).start();
             injector.getInstance(SnapshotShardsService.class).start();
             injector.getInstance(RoutingService.class).start();
             injector.getInstance(SearchService.class).start();
             nodeService.getMonitorService().start();
     //...
             Discovery discovery = injector.getInstance(Discovery.class);
           clusterService.getMasterService().setClusterStatePublisher(discovery::publish);
             discovery.start(); // start before cluster service so that it can set initial state on ClusterApplierService
             clusterService.start();

     裏面的每一個方法，都值得花時間去深刻研究下。哈哈。。。

總結

總的來看，Elasticsearch啓動過程三大步，第一步：加載各類配置信息，這些配置信息既有自定義的配置信息，也有機器的環境變量信息，它們告訴es，我想要建立一個什麼樣的節點。第二步：建立節點，節點具備各類各樣的功能，好比說執行搜索查詢請求、選主、與其餘節點同步集羣狀態信息……這些功能須要各類服務/插件/模塊Module來實現。第三步：啓動節點，其實就是各類模塊、插件、服務的啓動。

最後放一張整理上上面的9個方法的調用關係圖：

原文：https://www.cnblogs.com/hapjin/p/10124269.html