10. 上接RetryableEurekaHttpClient#execute，繼續執行clientFactory.newClient(currentEndpoint);返回的是new RedirectingEurekaHttpClient(endpoint.getServiceUrl(), delegateFactory, dnsService);requestExecutor.execute(currentHttpClient);即RedirectingEurekaHttpClient#execute

protected <R> EurekaHttpResponse<R> execute(RequestExecutor<R> requestExecutor) {
        EurekaHttpClient currentEurekaClient = delegateRef.get();
        if (currentEurekaClient == null) {
            AtomicReference<EurekaHttpClient> currentEurekaClientRef = new AtomicReference<>(factory.newClient(serviceEndpoint));
            try {
                EurekaHttpResponse<R> response = executeOnNewServer(requestExecutor, currentEurekaClientRef);
                TransportUtils.shutdown(delegateRef.getAndSet(currentEurekaClientRef.get()));
                return response;
            } catch (Exception e) {
                logger.error("Request execution error", e);
                TransportUtils.shutdown(currentEurekaClientRef.get());
                throw e;
            }
        } else {
            try {
                return requestExecutor.execute(currentEurekaClient);
            } catch (Exception e) {
                logger.error("Request execution error", e);
                delegateRef.compareAndSet(currentEurekaClient, null);
                currentEurekaClient.shutdown();
                throw e;
            }
        }
    }
 

這裡的factory.newClient(serviceEndpoint)即Jersey1TransportClientFactories#newTransportClientFactory返回的，執行下來是返回的是MetricsCollectingEurekaHttpClient，這裡的delegateFactory是JerseyEurekaHttpClientFactory，執行newClient後返回new JerseyApplicationClient(apacheClient, endpoint.getServiceUrl(), additionalHeaders);

return new MetricsCollectingEurekaHttpClient(
                        delegateFactory.newClient(endpoint),
                        metricsByRequestType,
                        exceptionMetrics,
                        false
                );
 

繼續執行

private <R> EurekaHttpResponse<R> executeOnNewServer(RequestExecutor<R> requestExecutor,
                                                         AtomicReference<EurekaHttpClient> currentHttpClientRef) {
        URI targetUrl = null;
        for (int followRedirectCount = 0; followRedirectCount < MAX_FOLLOWED_REDIRECTS; followRedirectCount++) {
            EurekaHttpResponse<R> httpResponse = requestExecutor.execute(currentHttpClientRef.get());
            if (httpResponse.getStatusCode() != 302) {
                if (followRedirectCount == 0) {
                    logger.debug("Pinning to endpoint {}", targetUrl);
                } else {
                    logger.info("Pinning to endpoint {}, after {} redirect(s)", targetUrl, followRedirectCount);
                }
                return httpResponse;
            }

            targetUrl = getRedirectBaseUri(httpResponse.getLocation());
            if (targetUrl == null) {
                throw new TransportException("Invalid redirect URL " + httpResponse.getLocation());
            }

            currentHttpClientRef.getAndSet(null).shutdown();
            currentHttpClientRef.set(factory.newClient(new DefaultEndpoint(targetUrl.toString())));
        }
        String message = "Follow redirect limit crossed for URI " + serviceEndpoint.getServiceUrl();
        logger.warn(message);
        throw new TransportException(message);
    }
 

繼續深度呼叫requestExecutor.execute(currentHttpClientRef.get());即MetricsCollectingEurekaHttpClient#execute

protected <R> EurekaHttpResponse<R> execute(RequestExecutor<R> requestExecutor) {
        EurekaHttpClientRequestMetrics requestMetrics = metricsByRequestType.get(requestExecutor.getRequestType());
        Stopwatch stopwatch = requestMetrics.latencyTimer.start();
        try {
            EurekaHttpResponse<R> httpResponse = requestExecutor.execute(delegate);
            requestMetrics.countersByStatus.get(mappedStatus(httpResponse)).increment();
            return httpResponse;
        } catch (Exception e) {
            requestMetrics.connectionErrors.increment();
            exceptionsMetric.count(e);
            throw e;
        } finally {
            stopwatch.stop();
        }
    }

這裡的requestExecutor.execute(delegate)代表JerseyApplicationClient的父類AbstractJerseyEurekaHttpClient執行getApplications，請求服務連結後最後返回結果應用資訊EurekaHttpResponse<Applications>

public EurekaHttpResponse<Applications> getApplications(String... regions) {
        return getApplicationsInternal("apps/", regions);
    }

 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 (logger.isDebugEnabled()) {
                logger.debug("Jersey HTTP GET {}/{}?{}; statusCode={}",
                        serviceUrl, urlPath,
                        regionsParamValue == null ? "" : "regions=" + regionsParamValue,
                        response == null ? "N/A" : response.getStatus()
                );
            }
            if (response != null) {
                response.close();
            }
        }
    }

記錄監控所需的各種返回碼狀態指標，如果是重定向302的話需要做額外的處理，在請求一次目標連結，最後返回。回到RetryableEurekaHttpClient#execute，判斷狀態儲存後返回DiscoveryClient#getAndStoreFullRegistry，打亂順序後儲存應用資訊localRegionApps.set(this.filterAndShuffle(apps));儲存應用資訊雜湊碼

private void shuffleInstances(boolean filterUpInstances, 
            boolean indexByRemoteRegions,
            @Nullable Map<String, Applications> remoteRegionsRegistry, 
            @Nullable EurekaClientConfig clientConfig,
            @Nullable InstanceRegionChecker instanceRegionChecker) {
        Map<String, VipIndexSupport> secureVirtualHostNameAppMap = new HashMap<>();
        Map<String, VipIndexSupport> virtualHostNameAppMap = new HashMap<>();
        for (Application application : appNameApplicationMap.values()) {
            if (indexByRemoteRegions) {
                application.shuffleAndStoreInstances(remoteRegionsRegistry, clientConfig, instanceRegionChecker);
            } else {
                application.shuffleAndStoreInstances(filterUpInstances);
            }
            this.addInstancesToVIPMaps(application, virtualHostNameAppMap, secureVirtualHostNameAppMap);
        }
        shuffleAndFilterInstances(virtualHostNameAppMap, filterUpInstances);
        shuffleAndFilterInstances(secureVirtualHostNameAppMap, filterUpInstances);

        this.virtualHostNameAppMap.putAll(virtualHostNameAppMap);
        this.virtualHostNameAppMap.keySet().retainAll(virtualHostNameAppMap.keySet());
        this.secureVirtualHostNameAppMap.putAll(secureVirtualHostNameAppMap);
        this.secureVirtualHostNameAppMap.keySet().retainAll(secureVirtualHostNameAppMap.keySet());
    }

11. DiscoveryClient#fetchRegistry釋出快取更新事件onCacheRefreshed();釋出遠端狀態更新事件updateInstanceRemoteStatus();如果查詢失敗則請求備用註冊地址fetchRegistryFromBackup();獲取應用資訊儲存起來。判斷是否在初始化時就向伺服器註冊本機資訊。

 if (clientConfig.shouldRegisterWithEureka() && clientConfig.shouldEnforceRegistrationAtInit()) {
            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);
            }
        }

12. 最後，初始化排程任務（例如叢集解析器、心跳、例項化資訊複製器、快取重新整理，狀態變化監聽器）

 private void initScheduledTasks() {
        if (clientConfig.shouldFetchRegistry()) {
            // registry cache refresh timer
            int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
            int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
            scheduler.schedule(
                    new TimedSupervisorTask(
                            "cacheRefresh",
                            scheduler,
                            cacheRefreshExecutor,
                            registryFetchIntervalSeconds,
                            TimeUnit.SECONDS,
                            expBackOffBound,
                            new CacheRefreshThread()
                    ),
                    registryFetchIntervalSeconds, TimeUnit.SECONDS);
        }

        if (clientConfig.shouldRegisterWithEureka()) {
            int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
            int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
            logger.info("Starting heartbeat executor: " + "renew interval is: {}", renewalIntervalInSecs);

            // Heartbeat timer
            scheduler.schedule(
                    new TimedSupervisorTask(
                            "heartbeat",
                            scheduler,
                            heartbeatExecutor,
                            renewalIntervalInSecs,
                            TimeUnit.SECONDS,
                            expBackOffBound,
                            new HeartbeatThread()
                    ),
                    renewalIntervalInSecs, TimeUnit.SECONDS);

            // InstanceInfo replicator
            instanceInfoReplicator = new InstanceInfoReplicator(
                    this,
                    instanceInfo,
                    clientConfig.getInstanceInfoReplicationIntervalSeconds(),
                    2); // burstSize

            statusChangeListener = new ApplicationInfoManager.StatusChangeListener() {
                @Override
                public String getId() {
                    return "statusChangeListener";
                }

                @Override
                public void notify(StatusChangeEvent statusChangeEvent) {
                    if (InstanceStatus.DOWN == statusChangeEvent.getStatus() ||
                            InstanceStatus.DOWN == statusChangeEvent.getPreviousStatus()) {
                        // log at warn level if DOWN was involved
                        logger.warn("Saw local status change event {}", statusChangeEvent);
                    } else {
                        logger.info("Saw local status change event {}", statusChangeEvent);
                    }
                    instanceInfoReplicator.onDemandUpdate();
                }
            };

            if (clientConfig.shouldOnDemandUpdateStatusChange()) {
                applicationInfoManager.registerStatusChangeListener(statusChangeListener);
            }

            instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
        } else {
            logger.info("Not registering with Eureka server per configuration");
        }
    }