【原创】Eureka源码之二：服务注册

// DiscoveryClient构造器中：
if (clientConfig.shouldRegisterWithEureka() && clientConfig.shouldEnforceRegistrationAtInit()) {
//配置了开启注册和强制注册初始化时，则会立马调用注册方法
    try {
        if (!register() ) {
            throw new IllegalStateException("Registration error at startup. Invalid server response.");
        }
    } catch (Throwable th) {
        logger.error("Registration error at startup: {}", th.getMessage());
        throw new IllegalStateException(th);
    }
}

-----------------------------------
// 实例信息复制器初始化，并且启动。
instanceInfoReplicator = new InstanceInfoReplicator(
        this,
        instanceInfo,
        clientConfig.getInstanceInfoReplicationIntervalSeconds(),
        2); // burstSize
instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
// InstanceInfoReplicator.java实现了RUNNABLE，接着看start方法
public void start(int initialDelayMs) {
    if (started.compareAndSet(false, true)) {
        instanceInfo.setIsDirty();  // for initial register
        // 30秒后执行当前对象任务
        Future next = scheduler.schedule(this, initialDelayMs, TimeUnit.SECONDS);
        scheduledPeriodicRef.set(next);
    }
}

public void run() {
    try {
        // 刷新实例信息
        discoveryClient.refreshInstanceInfo();
        // 判断实例信息是否发生改变
        // isInstanceInfoDirty默认为false，实例信息发生改变时会被设为true
        // 被设为ture，则dirtyTimestamp不为null，则发起注册请求
        Long dirtyTimestamp = instanceInfo.isDirtyWithTime();
        if (dirtyTimestamp != null) {
            // 注册
            discoveryClient.register();
            instanceInfo.unsetIsDirty(dirtyTimestamp);
        }
    } catch (Throwable t) {
        logger.warn("There was a problem with the instance info replicator", t);
    } finally {
        // 40秒后执行
        Future next = scheduler.schedule(this, replicationIntervalSeconds, TimeUnit.SECONDS);
        scheduledPeriodicRef.set(next);
    }
}

------------------------------------
 /**
 * 通过REST调用注册eureka服务
 */
boolean register() throws Throwable {
    logger.info(PREFIX + "{}: registering service...", appPathIdentifier);
    EurekaHttpResponse<Void> httpResponse;
    try {
        httpResponse = eurekaTransport.registrationClient.register(instanceInfo);
    } catch (Exception e) {
        logger.warn(PREFIX + "{} - registration failed {}", appPathIdentifier, e.getMessage(), e);
        throw e;
    }
    if (logger.isInfoEnabled()) {
        logger.info(PREFIX + "{} - registration status: {}", appPathIdentifier, httpResponse.getStatusCode());
    }
    // 根据响应状态码204判断是否注册成功
    return httpResponse.getStatusCode() == Status.NO_CONTENT.getStatusCode();
}

// DiscoveryClient构造器中：
if (clientConfig.shouldRegisterWithEureka() && clientConfig.shouldEnforceRegistrationAtInit()) {
//配置了开启注册和强制注册初始化时，则会立马调用注册方法
    try {
        if (!register() ) {
            throw new IllegalStateException("Registration error at startup. Invalid server response.");
        }
    } catch (Throwable th) {
        logger.error("Registration error at startup: {}", th.getMessage());
        throw new IllegalStateException(th);
    }
}

-----------------------------------
// 实例信息复制器初始化，并且启动。
instanceInfoReplicator = new InstanceInfoReplicator(
        this,
        instanceInfo,
        clientConfig.getInstanceInfoReplicationIntervalSeconds(),
        2); // burstSize
instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
// InstanceInfoReplicator.java实现了RUNNABLE，接着看start方法
public void start(int initialDelayMs) {
    if (started.compareAndSet(false, true)) {
        instanceInfo.setIsDirty();  // for initial register
        // 30秒后执行当前对象任务
        Future next = scheduler.schedule(this, initialDelayMs, TimeUnit.SECONDS);
        scheduledPeriodicRef.set(next);
    }
}

public void run() {
    try {
        // 刷新实例信息
        discoveryClient.refreshInstanceInfo();
        // 判断实例信息是否发生改变
        // isInstanceInfoDirty默认为false，实例信息发生改变时会被设为true
        // 被设为ture，则dirtyTimestamp不为null，则发起注册请求
        Long dirtyTimestamp = instanceInfo.isDirtyWithTime();
        if (dirtyTimestamp != null) {
            // 注册
            discoveryClient.register();
            instanceInfo.unsetIsDirty(dirtyTimestamp);
        }
    } catch (Throwable t) {
        logger.warn("There was a problem with the instance info replicator", t);
    } finally {
        // 40秒后执行
        Future next = scheduler.schedule(this, replicationIntervalSeconds, TimeUnit.SECONDS);
        scheduledPeriodicRef.set(next);
    }
}

------------------------------------
 /**
 * 通过REST调用注册eureka服务
 */
boolean register() throws Throwable {
    logger.info(PREFIX + "{}: registering service...", appPathIdentifier);
    EurekaHttpResponse<Void> httpResponse;
    try {
        httpResponse = eurekaTransport.registrationClient.register(instanceInfo);
    } catch (Exception e) {
        logger.warn(PREFIX + "{} - registration failed {}", appPathIdentifier, e.getMessage(), e);
        throw e;
    }
    if (logger.isInfoEnabled()) {
        logger.info(PREFIX + "{} - registration status: {}", appPathIdentifier, httpResponse.getStatusCode());
    }
    // 根据响应状态码204判断是否注册成功
    return httpResponse.getStatusCode() == Status.NO_CONTENT.getStatusCode();
}

■Eureka Client：

1）注册1：DisoverClient构造器里会根据是否开启立即调用注册Eureka Server接口进行注册；

2）注册2：实例信息复制器启动时会使用定时调度30秒延迟调用注册方法，如果实例信息发生改变，则之后会每隔40秒进行重新注册；

3）注册方式：使用Jersey HTTP向Eureka Server发起注册请求。

■Eureka Server：

1）启动：EurekaBootStrap启动入口，继承ServletContextListener。核心类：PeerAwareInstanceRegistryImpl；

2）Eureka Server注册逻辑：服务端本地缓存（队列）进行处理注册，比如：状态的更新、添加到近期变化队列等；

3）复制：集群环境下，节点之间需要进行注册信息的同步。除了本身节点，将会复制注册信息到其它对等节点，最后同样是使用Jersey进行请求同步注册。