Elasticsearch源码分析(一)启动流程

es启动脚本是bin目录下的elasticsearch。其中需要加载一些环境变量，诸如ES_CLASSPATH JAVA_OPTS  ES_JAVA_OPTS等。推荐设置ES_HEAP_SIZE的值，来这只es进程需要的内存（经验值为系统内存的一半以上），同时设置-p参数来指定pid文件的生成位置，在es关闭的时候会用到。

脚本内容不再赘述，java主类位于org.elasticsearch.bootstrap。主要逻辑是生成了一个InternalNode节点，并且启动了一个keepalive线程。结点的启动代表整个es进程启动了。

InternalNode节点是通过NodeBuilder来生成的，节点在构造函数中通过ModuleBuilder类来进行模块的注入（是对Guice的一个封装而已），同时生成injector实例，如下

            ModulesBuilder modules = new ModulesBuilder();
            modules.add(new Version.Module(version));
            modules.add(new CacheRecyclerModule(settings));
            modules.add(new PageCacheRecyclerModule(settings));
            modules.add(new BigArraysModule(settings));
            modules.add(new PluginsModule(settings, pluginsService));
            modules.add(new SettingsModule(settings));
            modules.add(new NodeModule(this));
            modules.add(new NetworkModule());
            modules.add(new ScriptModule(settings));
            modules.add(new EnvironmentModule(environment));
            modules.add(new NodeEnvironmentModule(nodeEnvironment));
            modules.add(new ClusterNameModule(settings));
            modules.add(new ThreadPoolModule(settings));
            modules.add(new DiscoveryModule(settings));
            modules.add(new ClusterModule(settings));
            modules.add(new RestModule(settings));
            modules.add(new TransportModule(settings));
            if (settings.getAsBoolean("http.enabled", true)) {
                modules.add(new HttpServerModule(settings));
            }
            modules.add(new RiversModule(settings));
            modules.add(new IndicesModule(settings));
            modules.add(new SearchModule());
            modules.add(new ActionModule(false));
            modules.add(new MonitorModule(settings));
            modules.add(new GatewayModule(settings));
            modules.add(new NodeClientModule());
            modules.add(new BulkUdpModule());
            modules.add(new ShapeModule());
            modules.add(new PercolatorModule());
            modules.add(new ResourceWatcherModule());
            modules.add(new RepositoriesModule());
            modules.add(new TribeModule());

            injector = modules.createInjector();

在InternalNode的start方法中，用injector对各个模块完成启动，各自负责各自的功能，如下：

        injector.getInstance(Discovery.class).setAllocationService(injector.getInstance(AllocationService.class));

        for (Class<? extends LifecycleComponent> plugin : pluginsService.services()) {
            injector.getInstance(plugin).start();
        }

        injector.getInstance(MappingUpdatedAction.class).start();
        injector.getInstance(IndicesService.class).start();
        injector.getInstance(IndexingMemoryController.class).start();
        injector.getInstance(IndicesClusterStateService.class).start();
        injector.getInstance(IndicesTTLService.class).start();
        injector.getInstance(RiversManager.class).start();
        injector.getInstance(SnapshotsService.class).start();
        injector.getInstance(ClusterService.class).start();
        injector.getInstance(RoutingService.class).start();
        injector.getInstance(SearchService.class).start();
        injector.getInstance(MonitorService.class).start();
        injector.getInstance(RestController.class).start();
        injector.getInstance(TransportService.class).start();
        DiscoveryService discoService = injector.getInstance(DiscoveryService.class).start();
        discoService.waitForInitialState();

        // gateway should start after disco, so it can try and recovery from gateway on "start"
        injector.getInstance(GatewayService.class).start();

        if (settings.getAsBoolean("http.enabled", true)) {
            injector.getInstance(HttpServer.class).start();
        }
        injector.getInstance(BulkUdpService.class).start();
        injector.getInstance(ResourceWatcherService.class).start();
        injector.getInstance(TribeService.class).start();

至此，es进程启动完毕。

guice相关介绍可以参见以下链接：

关键点在于：

@inject注释---guice会扫描inject注释，并对方法中出现的参数实例寻找对应注册的实例进行初始化。

bind接口-----将接口跟具体实现类绑定

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