Cloud : Eureka Client 端服务发现

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Github : 👉 github.com/black-ant
CASE 备份 : 👉 gitee.com/antblack/ca…

一 . 前言

文章目的 :

• 深入 Client 端服务发现的流程

概念补充 region：可以简单理解为地理上的分区，比如上海地区，或者广州地区，再或者北京等等，没有具体大小的限制。根据项目具体的情况，可以自行合理划分region。

zone：可以简单理解为region内的具体机房，比如说region划分为北京，然后北京有两个机房，就可以在此region之下划分出zone1,zone2两个zone。

二 . 调用的起点

2.1 初始化

Eureka Client 在初始化 EurekaClient 类的同时发起了服务发现的逻辑 , 主要调用流程为 :

• Step 1 : C- EurekaClientAutoConfiguration
  
  • PVC- RefreshableEurekaClientConfiguration 中进行 EurekaClient 的 Bean 加载
• Step 2 : 调用 DiscoveryClient 构造器
• Step 3 : Client 发起 FullRegistry 操作

Step 1 : Configuration 的 Bean 加载

public EurekaClient eurekaClient(ApplicationInfoManager manager,
      EurekaClientConfig config, EurekaInstanceConfig instance,
      @Autowired(required = false) HealthCheckHandler healthCheckHandler) {
   ApplicationInfoManager appManager;
   if (AopUtils.isAopProxy(manager)) {
      appManager = ProxyUtils.getTargetObject(manager);
   }
   else {
      appManager = manager;
   }
   // 构建 CloudEurekaClient 对象
   CloudEurekaClient cloudEurekaClient = new CloudEurekaClient(appManager,config, this.optionalArgs, this.context);
   // 注册健康检查对象
   cloudEurekaClient.registerHealthCheck(healthCheckHandler);
   return cloudEurekaClient;
}

// PS : 调用 CloudEurekaClient 构造器中会调用其父类 DiscoveryClient 的构造函数

Step 2 : DiscoveryClient full Registry

private boolean fetchRegistry(boolean forceFullRegistryFetch) {
    Stopwatch tracer = FETCH_REGISTRY_TIMER.start();

    try {
        // If the delta is disabled or if it is the first time, get all
        // applications
        Applications applications = getApplications();

        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
            {
            // 从eureka服务器获取完整的注册表信息并将其存储在本地
            getAndStoreFullRegistry();
        } else {
            getAndUpdateDelta(applications);
        }
        applications.setAppsHashCode(applications.getReconcileHashCode());
        logTotalInstances();
    } catch (Throwable e) {
 
    }

    // 在更新实例远程状态之前通知缓存刷新
    onCacheRefreshed();

    // 基于缓存中保存的刷新数据更新远程状态
    updateInstanceRemoteStatus();

    // 成功获取注册表，因此返回true
    return true;
}

Step 3 : 查询 Registry

private void getAndStoreFullRegistry() throws Throwable {
    long currentUpdateGeneration = fetchRegistryGeneration.get();

    Applications apps = null;
    
    // 通过 Client 获取 Applications
    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();
    }
    
    
     if (apps == null) {
           //............
     } else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
          // 重点 : 设置到  AtomicReference<Applications> 对象中
          localRegionApps.set(this.filterAndShuffle(apps));
     } else {
     }
}

三 . 服务的发现

从上面看到 , 通过 Client 搜索了 Registy 对象 , 后面看一下具体的查询流程

3.1 service 的获取

Step 1 : EurekaDiscoveryClient 发起请求

// EurekaDiscoveryClient 中通过如下代码获取 :
Applications applications = this.eurekaClient.getApplications();

// PS : 此处的 eurekaClient 为 CloudEurekaClient

Step 2 : 获取 Applications

// 这里是通过一个原之类缓存了所有的 Applications
private final AtomicReference<Applications> localRegionApps = new AtomicReference<Applications>();

public Applications getApplications() {
    return localRegionApps.get();
}

PS : Applications 数据如下

Step 3 : Applications 的缓存

上文知道了获取的时机 , 这里再来看一下数据是在什么时候缓存进去的 :

// 节点一 :　获取　Client Registry
private void getAndStoreFullRegistry() throws Throwable {
  // 上文看了 发起的流程 , 调用了一个 Client 发起
}


// 节点二 : 远程获取 Application
public EurekaHttpResponse<Applications> getApplications(final String... regions) {
    return execute(new RequestExecutor<Applications>() {
        @Override
        public EurekaHttpResponse<Applications> execute(EurekaHttpClient delegate) {
            return delegate.getApplications(regions);
        }

        @Override
        public RequestType getRequestType() {
            return RequestType.GetApplications;
        }
    });
}


// 节点三 : 循环调用不同的 HttpClient , 如下图总共提供了四种 HttpClient , 此处主要为 SessionedEurekaHttpClient
protected <R> EurekaHttpResponse<R> execute(RequestExecutor<R> requestExecutor) {
    long now = System.currentTimeMillis();
    long delay = now - lastReconnectTimeStamp;
    if (delay >= currentSessionDurationMs) {
        logger.debug("Ending a session and starting anew");
        lastReconnectTimeStamp = now;
        currentSessionDurationMs = randomizeSessionDuration(sessionDurationMs);
        TransportUtils.shutdown(eurekaHttpClientRef.getAndSet(null));
    }

    EurekaHttpClient eurekaHttpClient = eurekaHttpClientRef.get();
    if (eurekaHttpClient == null) {
        eurekaHttpClient = TransportUtils.getOrSetAnotherClient(eurekaHttpClientRef, clientFactory.newClient());
    }
    
    // 回调节点二传入的匿名对象
    return requestExecutor.execute(eurekaHttpClient);
}

// 节点四 : Internet 调用 , 可以看到调用的 app 接口 C- AbstractJerseyEurekaHttpClient
public EurekaHttpResponse<Applications> getApplications(String... regions) {
    return getApplicationsInternal("apps/", regions);
}

// 没想到啊没想到 , 这里居然看到了 jerseyClient , 这玩意这么底层的吗 C- 
private EurekaHttpResponse<Applications> getApplicationsInternal(String urlPath, String[] regions) {
    ClientResponse response = null;
    String regionsParamValue = null;
    try {
        WebResource webResource = jerseyClient.resource(serviceUrl).path(urlPath);
        if (regions != null && regions.length > 0) {
            regionsParamValue = StringUtil.join(regions);
            webResource = webResource.queryParam("regions", regionsParamValue);
        }
        Builder requestBuilder = webResource.getRequestBuilder();
        addExtraHeaders(requestBuilder);
        response = requestBuilder.accept(MediaType.APPLICATION_JSON_TYPE).get(ClientResponse.class);

        Applications applications = null;
        if (response.getStatus() == Status.OK.getStatusCode() && response.hasEntity()) {
            applications = response.getEntity(Applications.class);
        }
        return anEurekaHttpResponse(response.getStatus(), Applications.class)
                .headers(headersOf(response))
                .entity(applications)
                .build();
    } finally {

        if (response != null) {
            response.close();
        }
    }
}

补充 : Eureka HttpClient 体系

补充 : application 信息

[
    [{
        "host": "localhost",
        "port": 8088,
        "secure": false,
        "uri": "http://localhost:8088",
        "metadata": {
            "management.port": "8088"
        },
        "instanceId": "DESKTOP-TSNPTAK:GANG-EUREKA:8088",
        "serviceId": "GANG-EUREKA",
        "instanceInfo": {
            "instanceId": "DESKTOP-TSNPTAK:GANG-EUREKA:8088",
            "app": "GANG-EUREKA",
            "appGroupName": null,
            "ipAddr": "192.168.0.6",
            "sid": "na",
            "homePageUrl": "http://localhost:8088/",
            "statusPageUrl": "http://localhost:8088/actuator/info",
            "healthCheckUrl": "http://localhost:8088/actuator/health",
            "secureHealthCheckUrl": null,
            "vipAddress": "GANG-EUREKA",
            "secureVipAddress": "GANG-EUREKA",
            "countryId": 1,
            "dataCenterInfo": {
                "@class": "com.netflix.appinfo.InstanceInfo$DefaultDataCenterInfo",
                "name": "MyOwn"
            },
            "hostName": "localhost",
            "status": "UP",
            "overriddenStatus": "UNKNOWN",
            "leaseInfo": {
                "renewalIntervalInSecs": 30,
                "durationInSecs": 90,
                "registrationTimestamp": 1628746104090,
                "lastRenewalTimestamp": 1628748325836,
                "evictionTimestamp": 0,
                "serviceUpTimestamp": 1628746074745
            },
            "isCoordinatingDiscoveryServer": true,
            "metadata": {
                "management.port": "8088"
            },
            "lastUpdatedTimestamp": 1628746104090,
            "lastDirtyTimestamp": 1628746074064,
            "actionType": "ADDED",
            "asgName": null
        },
        "scheme": null
    }]
]

四 . 请求的使用

请求的使用可以参考 Feign 负载均衡 , 其本身也是从容器中获取 Server 列表

public Object getServicesList() {
    List<List<ServiceInstance>> servicesList = new ArrayList<>();
    //获取服务名称
    List<String> serviceNames = discoveryClient.getServices();
    for (String serviceName : serviceNames) {
        //获取服务中的实例列表
        List<ServiceInstance> serviceInstances = discoveryClient.getInstances(serviceName);
        servicesList.add(serviceInstances);
    }
    return servicesList;
}

Step : Applicaiton 的存储

public List<String> getServices() {
   LinkedHashSet<String> services = new LinkedHashSet<>();
   if (this.discoveryClients != null) {
       // 可以看到 , 这里从多个 discoveryClients 中获取 Services
      for (DiscoveryClient discoveryClient : this.discoveryClients) {
         List<String> serviceForClient = discoveryClient.getServices();
         if (serviceForClient != null) {
            services.addAll(serviceForClient);
         }
      }
   }
   return new ArrayList<>(services);
}

C- DiscoveryClient : 该对象在 2.1 Step 2 中设置了
AtomicReference<Applications> localRegionApps = new AtomicReference<Applications>();

五 . 总结

核心对象就是一个 AtomicReference ,通过 AbstractJerseyEurekaHttpClient 调用 /app 查询所有的 Server