前面已经剖析了Eureka初始化、Eureks服务注册，现在继续Eureka服务拉取。Eureka服务集群中，客户端会向服务端拉取已经注册的实例，实时更新注册服务列表。
〓Eureka Client
// DiscoveryClient实例创建时会调用服务拉取,默认开启拉取注册信息。 // 接着调用拉取注册方法，如果拉取失败，则从备份中拉取 if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
// 拉取服务失败，则从配置中获取备份注册全类名进行反射调用获取服务信息 fetchRegistryFromBackup();
} // 在Eureka Client初始化时，会初始化刷新缓存定时任务（每30秒），刷新缓存线程CacheRefreshThread class CacheRefreshThread implements Runnable {
public void run() {
refreshRegistry();
}
} void refreshRegistry() {
try {
boolean isFetchingRemoteRegionRegistries = isFetchingRemoteRegionRegistries();
boolean remoteRegionsModified = false;
// This makes sure that a dynamic change to remote regions to fetch is honored. String latestRemoteRegions = clientConfig.fetchRegistryForRemoteRegions();
if (null != latestRemoteRegions) {
String currentRemoteRegions = remoteRegionsToFetch.get();
if (!latestRemoteRegions.equals(currentRemoteRegions)) {
// Both remoteRegionsToFetch and AzToRegionMapper.regionsToFetch need to be in sync synchronized (instanceRegionChecker.getAzToRegionMapper()) {
if (remoteRegionsToFetch.compareAndSet(currentRemoteRegions, latestRemoteRegions)) {
String[] remoteRegions = latestRemoteRegions.split(",");
remoteRegionsRef.set(remoteRegions);
instanceRegionChecker.getAzToRegionMapper().setRegionsToFetch(remoteRegions);
remoteRegionsModified = true;
} else {
logger.info("Remote regions to fetch modified concurrently," +
" ignoring change from {} to {}", currentRemoteRegions, latestRemoteRegions);
}
}
} else {
// Just refresh mapping to reflect any DNS/Property change instanceRegionChecker.getAzToRegionMapper().refreshMapping();
}
}
// 拉取服务 boolean success = fetchRegistry(remoteRegionsModified);
if (success) {
registrySize = localRegionApps.get().size();
lastSuccessfulRegistryFetchTimestamp = System.currentTimeMillis();
}
if (logger.isDebugEnabled()) {
StringBuilder allAppsHashCodes = new StringBuilder();
allAppsHashCodes.append("Local region apps hashcode: ");
allAppsHashCodes.append(localRegionApps.get().getAppsHashCode());
allAppsHashCodes.append(", is fetching remote regions? ");
allAppsHashCodes.append(isFetchingRemoteRegionRegistries);
for (Map.Entry<String, Applications> entry : remoteRegionVsApps.entrySet()) {
allAppsHashCodes.append(", Remote region: ");
allAppsHashCodes.append(entry.getKey());
allAppsHashCodes.append(" , apps hashcode: ");
allAppsHashCodes.append(entry.getValue().getAppsHashCode());
}
logger.debug("Completed cache refresh task for discovery. All Apps hash code is {} ",
allAppsHashCodes.toString());
}
} catch (Throwable e) {
logger.error("Cannot fetch registry from server", e);
}
}
.... // 拉取注册服务 private boolean fetchRegistry(boolean forceFullRegistryFetch) {
Stopwatch tracer = FETCH_REGISTRY_TIMER.start();
try {
// 获取本地缓存注册信息 Applications applications = getApplications();
// 如果增量开关disabled或者是首次拉取，那么将会（全量拉取）拉取全部实例applications,否则只是增量拉取服务 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 {
logger.info("Disable delta property : {}", clientConfig.shouldDisableDelta());
logger.info("Single vip registry refresh property : {}", clientConfig.getRegistryRefreshSingleVipAddress());
logger.info("Force full registry fetch : {}", forceFullRegistryFetch);
logger.info("Application is null : {}", (applications == null));
logger.info("Registered Applications size is zero : {}",
(applications.getRegisteredApplications().size() == 0));
logger.info("Application version is -1: {}", (applications.getVersion() == -1));
getAndStoreFullRegistry();
} else {
// 增量拉取 getAndUpdateDelta(applications);
}
applications.setAppsHashCode(applications.getReconcileHashCode());
// 只是简单的统计下实例数，并且打印在日志上而已 logTotalInstances();
} catch (Throwable e) {
logger.error(PREFIX + appPathIdentifier + " - was unable to refresh its cache! status = " + e.getMessage(), e);
return false;
} finally {
if (tracer != null) {
tracer.stop();
}
}
// Notify about cache refresh before updating the instance remote status // 更新实例远程状态之前通知缓存更新 onCacheRefreshed();
// Update remote status based on refreshed data held in the cache // 根据缓存中保存的刷新数据更新远程状态 updateInstanceRemoteStatus();
// registry was fetched successfully, so return true return true;
} // 全量拉取 private void getAndStoreFullRegistry() throws Throwable {
// 当前更新代数(更新计数) long currentUpdateGeneration = fetchRegistryGeneration.get();
logger.info("Getting all instance registry info from the eureka server");
Applications apps = null;
// 调用到EurekaServer的ApplicationsResource-getContainers()方法全量获取注册信息 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();
}
logger.info("The response status is {}", httpResponse.getStatusCode());
if (apps == null) {
logger.error("The application is null for some reason. Not storing this information");
} else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
// 更新本地缓存注册服务信息，将其拉取到的信息进行过滤和打乱， // 对注册信息进行过滤，过滤后只缓存服务状态为UP的实例 localRegionApps.set(this.filterAndShuffle(apps));
logger.debug("Got full registry with apps hashcode {}", apps.getAppsHashCode());
} else {
logger.warn("Not updating applications as another thread is updating it already");
}
} // 将拉取到的服务进行过滤和打乱顺序，之后存放在remoteRegionVsApps private Applications filterAndShuffle(Applications apps) {
if (apps != null) {
if (isFetchingRemoteRegionRegistries()) {
Map<String, Applications> remoteRegionVsApps = new ConcurrentHashMap<String, Applications>();
apps.shuffleAndIndexInstances(remoteRegionVsApps, clientConfig, instanceRegionChecker);
for (Applications applications : remoteRegionVsApps.values()) {
applications.shuffleInstances(clientConfig.shouldFilterOnlyUpInstances());
}
this.remoteRegionVsApps = remoteRegionVsApps;
} else {
apps.shuffleInstances(clientConfig.shouldFilterOnlyUpInstances());
}
}
return apps;
} // 调用http get请求获取服务注册列表 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();
}
}
} // 查看拉取增量服务，同样的原理，只不过是向服务端请求时路径是app/delta来区分全部还是增量了。 private void getAndUpdateDelta(Applications applications) throws Throwable {
long currentUpdateGeneration = fetchRegistryGeneration.get();
Applications delta = null;
EurekaHttpResponse<Applications> httpResponse = eurekaTransport.queryClient.getDelta(remoteRegionsRef.get());
if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
delta = httpResponse.getEntity();
}
// 如果增量拉取不到服务，那么就进行全量拉取服务 if (delta == null) {
logger.warn("The server does not allow the delta revision to be applied because it is not safe. " + "Hence got the full registry.");
getAndStoreFullRegistry();
} else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
logger.debug("Got delta update with apps hashcode {}", delta.getAppsHashCode());
String reconcileHashCode = "";
if (fetchRegistryUpdateLock.tryLock()) {
try {
// 将增量拉取的服务更新到本地 updateDelta(delta);
reconcileHashCode = getReconcileHashCode(applications);
} finally {
fetchRegistryUpdateLock.unlock();
}
} else {
logger.warn("Cannot acquire update lock, aborting getAndUpdateDelta");
}
// There is a diff in number of instances for some reason // 由于某些原因造成实例数量不一致，那么会再次调用远程全量拉取服务 if (!reconcileHashCode.equals(delta.getAppsHashCode()) || clientConfig.shouldLogDeltaDiff()) {
reconcileAndLogDifference(delta, reconcileHashCode); // this makes a remoteCall }
} else {
logger.warn("Not updating application delta as another thread is updating it already");
logger.debug("Ignoring delta update with apps hashcode {}, as another thread is updating it already", delta.getAppsHashCode());
}
}```
客户端拉取服务存在全量拉取和增量拉取两种方式，在增量拉取的时候如果拉取失败，还是会再用全量拉取的方式去拉取服务。
〓Eureka Server
// 全量服务拉取接口 @GET public Response getContainers(@PathParam("version") String version,
@HeaderParam(HEADER_ACCEPT) String acceptHeader,
@HeaderParam(HEADER_ACCEPT_ENCODING) String acceptEncoding,
@HeaderParam(EurekaAccept.HTTP_X_EUREKA_ACCEPT) String eurekaAccept,
@Context UriInfo uriInfo,
@Nullable @QueryParam("regions") String regionsStr) {
boolean isRemoteRegionRequested = null != regionsStr && !regionsStr.isEmpty();
String[] regions = null;
if (!isRemoteRegionRequested) {
EurekaMonitors.GET_ALL.increment();
} else {
regions = regionsStr.toLowerCase().split(",");
Arrays.sort(regions); // So we don't have different caches for same regions queried in different order. EurekaMonitors.GET_ALL_WITH_REMOTE_REGIONS.increment();
}
// Check if the server allows the access to the registry. The server can // restrict access if it is not // ready to serve traffic depending on various reasons. // 检查eureka server服务是否允许访问（无法提供服务），不允许则返回403 if (!registry.shouldAllowAccess(isRemoteRegionRequested)) {
return Response.status(Status.FORBIDDEN).build();
}
CurrentRequestVersion.set(Version.toEnum(version));
KeyType keyType = Key.KeyType.JSON;
String returnMediaType = MediaType.APPLICATION_JSON;
// 没有指定接收的类型，默认则返回XML格式 if (acceptHeader == null || !acceptHeader.contains(HEADER_JSON_VALUE)) {
keyType = Key.KeyType.XML;
returnMediaType = MediaType.APPLICATION_XML;
}
Key cacheKey = new Key(Key.EntityType.Application,
ResponseCacheImpl.ALL_APPS,
keyType, CurrentRequestVersion.get(), EurekaAccept.fromString(eurekaAccept), regions
);
// 从缓存中获取服务 Response response;
if (acceptEncoding != null && acceptEncoding.contains(HEADER_GZIP_VALUE)) {
response = Response.ok(responseCache.getGZIP(cacheKey))
.header(HEADER_CONTENT_ENCODING, HEADER_GZIP_VALUE)
.header(HEADER_CONTENT_TYPE, returnMediaType)
.build();
} else {
response = Response.ok(responseCache.get(cacheKey))
.build();
}
return response;
}
// 增量服务拉取服务，跟全量拉取服务相似 @Path("delta") @GET public Response getContainerDifferential(
@PathParam("version") String version,
@HeaderParam(HEADER_ACCEPT) String acceptHeader,
@HeaderParam(HEADER_ACCEPT_ENCODING) String acceptEncoding,
@HeaderParam(EurekaAccept.HTTP_X_EUREKA_ACCEPT) String eurekaAccept,
@Context UriInfo uriInfo, @Nullable @QueryParam("regions") String regionsStr) {
boolean isRemoteRegionRequested = null != regionsStr && !regionsStr.isEmpty();
// If the delta flag is disabled in discovery or if the lease expiration // has been disabled, redirect clients to get all instances // 服务配置是否禁用增量，或者eureka server无法提供服务，则返回403，这样就能让客户端重新去请求全量服务接口 if ((serverConfig.shouldDisableDelta()) || (!registry.shouldAllowAccess(isRemoteRegionRequested))) {
return Response.status(Status.FORBIDDEN).build();
}
String[] regions = null;
if (!isRemoteRegionRequested) {
EurekaMonitors.GET_ALL_DELTA.increment();
} else {
regions = regionsStr.toLowerCase().split(",");
Arrays.sort(regions); // So we don't have different caches for same regions queried in different order. EurekaMonitors.GET_ALL_DELTA_WITH_REMOTE_REGIONS.increment();
}
CurrentRequestVersion.set(Version.toEnum(version));
KeyType keyType = Key.KeyType.JSON;
String returnMediaType = MediaType.APPLICATION_JSON;
if (acceptHeader == null || !acceptHeader.contains(HEADER_JSON_VALUE)) {
keyType = Key.KeyType.XML;
returnMediaType = MediaType.APPLICATION_XML;
}
// 构建缓存键 Key cacheKey = new Key(Key.EntityType.Application,
ResponseCacheImpl.ALL_APPS_DELTA,
keyType, CurrentRequestVersion.get(), EurekaAccept.fromString(eurekaAccept), regions
);
// 从缓存中获取服务信息 if (acceptEncoding != null && acceptEncoding.contains(HEADER_GZIP_VALUE)) {
return Response.ok(responseCache.getGZIP(cacheKey))
.header(HEADER_CONTENT_ENCODING, HEADER_GZIP_VALUE)
.header(HEADER_CONTENT_TYPE, returnMediaType)
.build();
} else {
return Response.ok(responseCache.get(cacheKey))
.build();
}
}
// 从缓存获取 Value getValue(final Key key, boolean useReadOnlyCache) {
Value payload = null;
try {
// 允许只读缓存，则从readOnlyCacheMap获取，否则从读写缓存readWriteCacheMap中获取 // readWriteCacheMap使用Guava cahce if (useReadOnlyCache) {
final Value currentPayload = readOnlyCacheMap.get(key);
if (currentPayload != null) {
payload = currentPayload;
} else {
payload = readWriteCacheMap.get(key);
readOnlyCacheMap.put(key, payload);
}
} else {
payload = readWriteCacheMap.get(key);
}
} catch (Throwable t) {
logger.error("Cannot get value for key : {}", key, t);
}
return payload;
}
总结
1）Eureka client拉取服务有两种方式：全量和增量，增量拉取失败则会再请求全量拉取。客户端可能会有两种方式去拉取服务，一个是在客户端启动时，如果配置有开启就会马上拉取服务，另外一个是定时更新缓存服务，定时会向服务端拉取服务。
2）Eureka server接收到请求时，会从自己的缓存中获取服务然后返回给客户端。
