Eureka - 服务发现

在Eureka - Client服务启动我们看到，注册表获取的地方有两个，一个是EurekaClient构造函数，一个是定时器每隔30秒去获取。我们先看看定时器TimedSupervisorTask的run方法

定时器

这个方法有三个比较重要的参数，timeoutMillis、delay、maxDelay。比如频率是30s，那这个maxDelay就是30*10=300s（这个10的来源参考上一篇），delay在这里是每次都翻倍，但是不能比maxDelay大。
整个设计思路是，如果调用30s超时，那就用60秒，如果再超时，就一直翻，但是不能超过300s。如果在后面的调用中正常了，那delay就恢复到30s，下次超时继续翻倍。

@Override
public void run() {
    Future<?> future = null;
    try {
        // 执行任务
        future = executor.submit(task);
        threadPoolLevelGauge.set((long) executor.getActiveCount());
        // 指定超时时间
        future.get(timeoutMillis, TimeUnit.MILLISECONDS);  // block until done or timeout
        //设置delay
        delay.set(timeoutMillis);
        threadPoolLevelGauge.set((long) executor.getActiveCount());
        successCounter.increment();
    } catch (TimeoutException e) {
        logger.warn("task supervisor timed out", e);
        timeoutCounter.increment();
        // 获取delay
        long currentDelay = delay.get();
        // maxDelay和currentDelay的2倍中取最小值
        long newDelay = Math.min(maxDelay, currentDelay * 2);
        // 设置为上面最小值
        delay.compareAndSet(currentDelay, newDelay);

    } catch (RejectedExecutionException e) {
        // 其他的略
        rejectedCounter.increment();
    } catch (Throwable e) {
        // 其他的略
        throwableCounter.increment();
    } finally {
        if (future != null) {
            future.cancel(true);
        }
        // 把任务放入定时器，时间是delay
        if (!scheduler.isShutdown()) {
            scheduler.schedule(this, delay.get(), TimeUnit.MILLISECONDS);
        }
    }
}

服务发现

判断增量获取还是全量获取

private boolean fetchRegistry(boolean forceFullRegistryFetch) {
    Stopwatch tracer = FETCH_REGISTRY_TIMER.start();
    try {
        Applications applications = getApplications();
        // 禁用增量、强制全量更新、没有注册信息的时候，进行全量更新
        if (clientConfig.shouldDisableDelta()
                || (!Strings.isNullOrEmpty(clientConfig.getRegistryRefreshSingleVipAddress()))
                || forceFullRegistryFetch
                || (applications == null)
                || (applications.getRegisteredApplications().size() == 0)
                || (applications.getVersion() == -1)) //Client application does not have latest library supporting delta
        {
            // 其他日志打印略
            getAndStoreFullRegistry();
        } else {
            //增量更新
            getAndUpdateDelta(applications);
        }
        // 计算hash
        applications.setAppsHashCode(applications.getReconcileHashCode());
        logTotalInstances();
    } catch (Throwable e) {
        // 其他日志打印略
        return false;
    } finally {
        if (tracer != null) {
            tracer.stop();
        }
    }
    // 其他略
    return true;
}

全量获取

全量获取，调用注册中心地址+apps/获取。

private void getAndStoreFullRegistry() throws Throwable {
    // 其他略
    Applications apps = null;
    // 调用注册中心地址+apps/获取
    EurekaHttpResponse<Applications> httpResponse = clientConfig.getRegistryRefreshSingleVipAddress() == null
            ? eurekaTransport.queryClient.getApplications(remoteRegionsRef.get())
            : eurekaTransport.queryClient.getVip(clientConfig.getRegistryRefreshSingleVipAddress(), remoteRegionsRef.get());
    if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
        apps = httpResponse.getEntity();
    }
    // 其他略
}

增量获取

增量更新，获取后，通过hash要判断是否和服务器一致，不一致就全量

private void getAndUpdateDelta(Applications applications) throws Throwable {
    long currentUpdateGeneration = fetchRegistryGeneration.get();

    Applications delta = null;
    // 调用注册中心地址+apps/delta获取
    EurekaHttpResponse<Applications> httpResponse = eurekaTransport.queryClient.getDelta(remoteRegionsRef.get());
    if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
        delta = httpResponse.getEntity();
    }

    if (delta == null) {
        //获取不到数据，全力更新
        getAndStoreFullRegistry();
    } else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
        logger.debug("Got delta update with apps hashcode {}", delta.getAppsHashCode());
        String reconcileHashCode = "";
        //加锁
        if (fetchRegistryUpdateLock.tryLock()) {
            try {
                // 和本地的合并
                updateDelta(delta);
                // 计算hash
                reconcileHashCode = getReconcileHashCode(applications);
            } finally {
                //解锁
                fetchRegistryUpdateLock.unlock();
            }
        } else {
            logger.warn("Cannot acquire update lock, aborting getAndUpdateDelta");
        }
        // There is a diff in number of instances for some reason
        // 和服务器的hash对比
        if (!reconcileHashCode.equals(delta.getAppsHashCode()) || clientConfig.shouldLogDeltaDiff()) {
            // 不一致说明和服务器的不一致，直接全量
            reconcileAndLogDifference(delta, reconcileHashCode);  // this makes a remoteCall
        }
    } else {
        // 其他略
    }
}

和本地数据的合并，包括新增、修改、删除。

private void updateDelta(Applications delta) {
    int deltaCount = 0;
    // 遍历所有增量
    for (Application app : delta.getRegisteredApplications()) {
        // 遍历所有实例
        for (InstanceInfo instance : app.getInstances()) {
            // 本地缓存
            Applications applications = getApplications();
            String instanceRegion = instanceRegionChecker.getInstanceRegion(instance);
            // 是否为同一个region，如果不是，则取同一个region的applications
            if (!instanceRegionChecker.isLocalRegion(instanceRegion)) {
                Applications remoteApps = remoteRegionVsApps.get(instanceRegion);
                if (null == remoteApps) {
                    remoteApps = new Applications();
                    remoteRegionVsApps.put(instanceRegion, remoteApps);
                }
                applications = remoteApps;
            }

            ++deltaCount;
            if (ActionType.ADDED.equals(instance.getActionType())) {
                // 新增处理
                Application existingApp = applications.getRegisteredApplications(instance.getAppName());
                if (existingApp == null) {
                    applications.addApplication(app);
                }
                logger.debug("Added instance {} to the existing apps in region {}", instance.getId(), instanceRegion);
                applications.getRegisteredApplications(instance.getAppName()).addInstance(instance);
            } else if (ActionType.MODIFIED.equals(instance.getActionType())) {
                // 修改处理
                Application existingApp = applications.getRegisteredApplications(instance.getAppName());
                if (existingApp == null) {
                    applications.addApplication(app);
                }
                logger.debug("Modified instance {} to the existing apps ", instance.getId());
                // 和新增都是调用addInstance方法，因为Application#addInstance里是先移除再新增，所有修改也可以调用
                applications.getRegisteredApplications(instance.getAppName()).addInstance(instance);

            } else if (ActionType.DELETED.equals(instance.getActionType())) {
                // 删除处理
                Application existingApp = applications.getRegisteredApplications(instance.getAppName());
                if (existingApp != null) {
                    logger.debug("Deleted instance {} to the existing apps ", instance.getId());
                    existingApp.removeInstance(instance);
                    if (existingApp.getInstancesAsIsFromEureka().isEmpty()) {
                        applications.removeApplication(existingApp);
                    }
                }
            }
        }
    }
    logger.debug("The total number of instances fetched by the delta processor : {}", deltaCount);
    
    getApplications().setVersion(delta.getVersion());
    getApplications().shuffleInstances(clientConfig.shouldFilterOnlyUpInstances());

    for (Applications applications : remoteRegionVsApps.values()) {
        applications.setVersion(delta.getVersion());
        applications.shuffleInstances(clientConfig.shouldFilterOnlyUpInstances());
    }
}