Elasticsearch6.3.2启动过程源码阅读记录

Elasticsearch6.3.2启动过程源码阅读记录

网上有很多关于es的源码分析，觉得自己技术深度还不够，所以这些文章只是看源码过程中的一个笔记，谈不上分析。

整个启动过程以类名.方法名，按顺序依次描述如下：

1. Elasticsearch.main启动入口类，注册JVM关闭钩子用来清理资源。

2. Command.mainwithoutErrorHandling 在es正式启动之前，加载一些命令：比如 ./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加载配置参数

           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中的配置参数

   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执行初始化命令。另外在源码中还有看到一些有趣的注释，比如必须设置java.io.tmpdir，这个参数在 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正式开始启动ElasticSearch。This method is invoked by {@link Elasticsearch#main(String[])} to startup elasticsearch。

   • 创建节点启动时需要的环境变量参数

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

   • checkLucene()检查匹配的Lucene jar包。

   • 创建节点，在下面Node构造方法中将详细分析这个过程。

             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 构造方法 Node(final Environment environment, Collection<Class<? extends Plugin>> classpathPlugins)。在这个构建方法里面，完成了创建一个节点所需的各种信息，这个方法非常重要，下面就例举出几个节点创建过程中几个重要的流程：

   • 设置节点环境变量信息(A component that holds all data paths for a single node.)

   nodeEnvironment = new NodeEnvironment(tmpSettings, environment);
   

   ​

   • 构造插件服务(PluginService)，

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

     看这个构造方法的注释：

         /**
          * 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) {
     

     其实就是加载：elasticsearch-6.3.2/modules 和 elasticsearch-6.3.2/plugins两个目录下的内容。
     
     

     ​

   • 创建自定义的线程池，节点执行各种任务用的吧。

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

     ​

   • 创建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)各种分词器。

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

     ​

   • SettingsModule(A module that binds the provided settings to the {@link Settings} interface) 各种配置参数用到。比如 jvm.options 和 elasticsearch.yml里面配置的各种参数。

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

     ​

   • 节点是集群的一份子，肯定需要集群相关的服务

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

     ​

   • 集群信息相关服务(Interface for a class used to gather information about a cluster at regular intervals) 周期性同步集群状态。

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

     ​

   • 创建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);
                 }
     

     比如：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));
     

     还有 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);
     

     还有 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:

     ​

     最终关联了一大批的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());
     

   总之，Node.java的构造方法里面实现了创建一个ElasticSearch节点所必须的各种信息，想要了解ElasticSearch节点的内部结构，应该就得多看看这个方法里面的代码吧。

2. ModulesBuilder.createInjector 使用了Guice 依赖注入。

               injector = modules.createInjector();
   

3. Node.start，前面创建了节点，现在开始启动节点。(Start the node. If the node is already started, this method is no-op)

   • 先拿到对象实例，再启动

             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();
     

     里面的每个方法，都值得花时间去深入研究下。哈哈。。。

总结

总的来看，Elasticsearch启动过程三大步，第一步：加载各种配置信息，这些配置信息既有自定义的配置信息，也有机器的环境变量信息，它们告诉es，我想要创建一个什么样的节点。第二步：创建节点，节点具有各种各样的功能，比如说执行搜索查询请求、选主、与其他节点同步集群状态信息……这些功能需要各种服务/插件/模块Module来实现。第三步：启动节点，其实就是各种模块、插件、服务的启动。

最后放一张整理上上面的9个方法的调用关系图：

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