之前我们分析了eureka cilent和eureka server的配置,下面我们来分析一下eureka的启动流程。先来介绍一个类EurekaBootStrap,这个类实现了ServletContextListener接口,在servlet容器启动时初始化EurekaServer。来看一下具体的实现

public void contextInitialized(ServletContextEvent event) {
    try {
        // 初始化 Eureka-Server 配置环境
        initEurekaEnvironment();

        // 初始化 Eureka-Server 上下文
        initEurekaServerContext();

        ServletContext sc = event.getServletContext();
        sc.setAttribute(EurekaServerContext.class.getName(), serverContext);
    } catch (Throwable e) {
        logger.error("Cannot bootstrap eureka server :", e);
        throw new RuntimeException("Cannot bootstrap eureka server :", e);
    }
}

看下initEurekaEnvironment方法

protected void initEurekaEnvironment() throws Exception {
    logger.info("Setting the eureka configuration..");

    // 设置配置文件的数据中心
    String dataCenter = ConfigurationManager.getConfigInstance().getString(EUREKA_DATACENTER);
    if (dataCenter == null) {
        logger.info("Eureka data center value eureka.datacenter is not set, defaulting to default");
        ConfigurationManager.getConfigInstance().setProperty(ARCHAIUS_DEPLOYMENT_DATACENTER, DEFAULT);
    } else {
        ConfigurationManager.getConfigInstance().setProperty(ARCHAIUS_DEPLOYMENT_DATACENTER, dataCenter);
    }

    // 设置配置文件的环境
    String environment = ConfigurationManager.getConfigInstance().getString(EUREKA_ENVIRONMENT);
    if (environment == null) {
        ConfigurationManager.getConfigInstance().setProperty(ARCHAIUS_DEPLOYMENT_ENVIRONMENT, TEST);
        logger.info("Eureka environment value eureka.environment is not set, defaulting to test");
    }
}

再看下initEurekaServerContext方法

protected void initEurekaServerContext() throws Exception {
    // 【2.2.1】创建 Eureka-Server 配置
    EurekaServerConfig eurekaServerConfig = new DefaultEurekaServerConfig();

    // 【2.2.2】Eureka-Server 请求和响应的数据兼容
    // For backward compatibility
    JsonXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(), XStream.PRIORITY_VERY_HIGH);
    XmlXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(), XStream.PRIORITY_VERY_HIGH);

    // 【2.2.3】创建 Eureka-Server 请求和响应编解码器
    logger.info("Initializing the eureka client...");
    logger.info(eurekaServerConfig.getJsonCodecName());
    ServerCodecs serverCodecs = new DefaultServerCodecs(eurekaServerConfig);

    // 【2.2.4】创建 Eureka-Client
    ApplicationInfoManager applicationInfoManager;
    if (eurekaClient == null) {
        EurekaInstanceConfig instanceConfig = isCloud(ConfigurationManager.getDeploymentContext())
                ? new CloudInstanceConfig()
                : new MyDataCenterInstanceConfig();
        
        applicationInfoManager = new ApplicationInfoManager(
                instanceConfig, new EurekaConfigBasedInstanceInfoProvider(instanceConfig).get());
        
        EurekaClientConfig eurekaClientConfig = new DefaultEurekaClientConfig();
        eurekaClient = new DiscoveryClient(applicationInfoManager, eurekaClientConfig);
    } else {
        applicationInfoManager = eurekaClient.getApplicationInfoManager();
    }

    // 【2.2.5】创建 应用实例信息的注册表
    PeerAwareInstanceRegistry registry;
    if (isAws(applicationInfoManager.getInfo())) { // AWS 相关，跳过
        registry = new AwsInstanceRegistry(
                eurekaServerConfig,
                eurekaClient.getEurekaClientConfig(),
                serverCodecs,
                eurekaClient
        );
        awsBinder = new AwsBinderDelegate(eurekaServerConfig, eurekaClient.getEurekaClientConfig(), registry, applicationInfoManager);
        awsBinder.start();
    } else {
        registry = new PeerAwareInstanceRegistryImpl(
                eurekaServerConfig,
                eurekaClient.getEurekaClientConfig(),
                serverCodecs,
                eurekaClient
        );
    }

    // 【2.2.6】创建 Eureka-Server 集群节点集合
    PeerEurekaNodes peerEurekaNodes = getPeerEurekaNodes(
            registry,
            eurekaServerConfig,
            eurekaClient.getEurekaClientConfig(),
            serverCodecs,
            applicationInfoManager
    );

    // 【2.2.7】创建 Eureka-Server 上下文
    serverContext = new DefaultEurekaServerContext(
            eurekaServerConfig,
            serverCodecs,
            registry,
            peerEurekaNodes,
            applicationInfoManager
    );

    // 【2.2.8】初始化 EurekaServerContextHolder
    EurekaServerContextHolder.initialize(serverContext);

    // 【2.2.9】初始化 Eureka-Server 上下文
    serverContext.initialize();
    logger.info("Initialized server context");

    // 【2.2.10】从其他 Eureka-Server 拉取注册信息
    // Copy registry from neighboring eureka node
    int registryCount = registry.syncUp();
    registry.openForTraffic(applicationInfoManager, registryCount);

    // 【2.2.11】注册监控
    // Register all monitoring statistics.
    EurekaMonitors.registerAllStats();
}

创建EurekaServer集群结点集合

PeerEurekaNodes peerEurekaNodes = getPeerEurekaNodes(
            registry,
            eurekaServerConfig,
            eurekaClient.getEurekaClientConfig(),
            serverCodecs,
            applicationInfoManager
    );

创建DefaultEurekaServerContext

serverContext = new DefaultEurekaServerContext(
            eurekaServerConfig,
            serverCodecs,
            registry,
            peerEurekaNodes,
            applicationInfoManager
    );

注册监控

EurekaMonitors.registerAllStats();

EurekaServer启动流程就完成了。
EurekaBootStrap就分析到这里了。