在Eureka源码-2-eurekaServer端对服务注册的处理 中，了解到了eureka server 将eureka client发送的服务注册请求中的实例信息保存到一个ConcurrentHashMap中来完成服务注册，这篇文章将在客户端的角度，来学习客户端如何查询服务地址列表。
Eureka有两个地方会触发服务地址列表的查询
- DiscoveryClient构造方法中会触发
- 30s执行一次的定时任务
客户端逻辑入口是DiscoveryClient 这个类，它的构造方法中有一个很好的设计：衰减执行，举个例子，第一次执行，间隔5s，第二次执行，可能是间隔10s,再次执行，可能是间隔20s才执行，这样做是为了防止网络抖动，请求不通时，继续进行无效的请求。
com.netflix.discovery.DiscoveryClient#initScheduledTasks
private void initScheduledTasks() {
if (clientConfig.shouldFetchRegistry()) {
// registry cache refresh timer
int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
cacheRefreshTask = new TimedSupervisorTask(
"cacheRefresh",
scheduler,
cacheRefreshExecutor,
registryFetchIntervalSeconds,
TimeUnit.SECONDS,
expBackOffBound,
new CacheRefreshThread()
);
scheduler.schedule(
cacheRefreshTask,
registryFetchIntervalSeconds, TimeUnit.SECONDS);
}
com.netflix.discovery.TimedSupervisorTask#run
@Override
public void run() {
Future<?> future = null;
try {
future = executor.submit(task);
threadPoolLevelGauge.set((long) executor.getActiveCount());
future.get(timeoutMillis, TimeUnit.MILLISECONDS); // block until done or timeout
// 重置delay
delay.set(timeoutMillis);
threadPoolLevelGauge.set((long) executor.getActiveCount());
successCounter.increment();
} catch (TimeoutException e) {
logger.warn("task supervisor timed out", e);
timeoutCounter.increment();
long currentDelay = delay.get();
//动态计算delay
long newDelay = Math.min(maxDelay, currentDelay * 2);
delay.compareAndSet(currentDelay, newDelay);
} catch (RejectedExecutionException e) {
if (executor.isShutdown() || scheduler.isShutdown()) {
logger.warn("task supervisor shutting down, reject the task", e);
} else {
logger.warn("task supervisor rejected the task", e);
}
rejectedCounter.increment();
} catch (Throwable e) {
if (executor.isShutdown() || scheduler.isShutdown()) {
logger.warn("task supervisor shutting down, can't accept the task");
} else {
logger.warn("task supervisor threw an exception", e);
}
throwableCounter.increment();
} finally {
if (future != null) {
future.cancel(true);
}
if (!scheduler.isShutdown()) {
// 如果任务没有关闭，那么继续延期执行，这里的delay是动态计算的，如果请求不通的话，就更改delay，使任务 延期执行
scheduler.schedule(this, delay.get(), TimeUnit.MILLISECONDS);
}
}
}
CacheRefreshThread ：
class CacheRefreshThread implements Runnable {
public void run() {
refreshRegistry();
}
}
com.netflix.discovery.DiscoveryClient#refreshRegistry 方法中，主要的操作：fetchRegistry(remoteRegionsModified);
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();
}
}
boolean success = fetchRegistry(remoteRegionsModified);
if (success) {
registrySize = localRegionApps.get().size(); // 从本地缓存中获取应用信息
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);
}
} catch (Throwable e) {
logger.error("Cannot fetch registry from server", e);
}
}
@Override
public Applications getApplications() {
return localRegionApps.get(); // 从本地缓存中获取应用信息，添加缓存是在DiscoveryClient#getAndStoreFullRegistry 中
}
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
// 取出本地缓存的服务列表信息
Applications applications = getApplications();
//满足如下条件会进行全量更新： 1. 是否禁用增量更新；2. 是否对某个region特别关注；3. 外部调用时是否通过入参指定全量更新；4. 本地还未缓存有效的服务列表信息；
if (clientConfig.shouldDisableDelta()
|| (!Strings.isNullOrEmpty(clientConfig.getRegistryRefreshSingleVipAddress()))
|| forceFullRegistryFetch
|| (applications == null) // 本地缓存中没有拿到，要进行全量更新
|| (applications.getRegisteredApplications().size() == 0)
|| (applications.getVersion() == -1)) //Client application does not have latest library supporting delta
{
// 全量更新
getAndStoreFullRegistry();
} else {
// 增量更新
getAndUpdateDelta(applications);
}
//重新计算和设置一致性hash码
applications.setAppsHashCode(applications.getReconcileHashCode());
logTotalInstances(); //日志打印所有应用的所有实例数之和
} catch (Throwable e) {
logger.error(PREFIX + "{} - was unable to refresh its cache! status = {}", appPathIdentifier, e.getMessage(), e);
return false;
} finally {
if (tracer != null) {
tracer.stop();
}
}
// Notify about cache refresh before updating the instance remote status
//将本地缓存更新的事件广播给所有已注册的监听器，注意该方法已被CloudEurekaClient类重写
onCacheRefreshed();
// Update remote status based on refreshed data held in the cache
/**检查刚刚更新的缓存中，有来自Eureka server的服务列表，其中包含了当前应用的状态，当前实例的成员变量lastRemoteInstanceStatus，记录的是最后一次更新的当前应用状态，上述两种状态在updateInstanceRemoteStatus方法中作比较 ，如果不一致，就更新lastRemoteInstanceStatus，并且广播对应的事件 **/
updateInstanceRemoteStatus();
// registry was fetched successfully, so return true
return true;
}
- DiscoveryClient#getAndStoreFullRegistry
从eureka server端获取服务注册中心的地址信息，然后更新并设置到本地缓存 localRegionApps ：
private final AtomicReference localRegionApps = new AtomicReference();
private void getAndStoreFullRegistry() throws Throwable {
long currentUpdateGeneration = fetchRegistryGeneration.get();
logger.info("Getting all instance registry info from the eureka server");
Applications apps = null;
EurekaHttpResponse<Applications> httpResponse = clientConfig.getRegistryRefreshSingleVipAddress() == null
? eurekaTransport.queryClient.getApplications(remoteRegionsRef.get()) // 调用接口向erureka server注册
: eurekaTransport.queryClient.getVip(clientConfig.getRegistryRefreshSingleVipAddress(), remoteRegionsRef.get());
if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
// 将注册中心返回的实例信息赋值给apps
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)) {
// 添加到本地缓存
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");
}
}
- 服务端查询服务地址流程
eurekaTransport.queryClient.getApplications(remoteRegionsRef.get()) 就是向eureka server发起服务注册请求，服务端会有一个接收地址。客户端发起服务地址的查询有两种，一种是全量、另一种是增量。对于全量查询请求，会调用Eureka-server的ApplicationsResource的getContainers方法，对于增量请求，会调用ApplicationsResource.getContainerDifferential。
- ApplicationsResource.getContainers
接收客户端发送的获取全量注册信息请求
@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. 服务端无法提供服务，返回403
if (!registry.shouldAllowAccess(isRemoteRegionRequested)) {
return Response.status(Status.FORBIDDEN).build();
}
CurrentRequestVersion.set(Version.toEnum(version));
KeyType keyType = Key.KeyType.JSON; // 设置返回数据格式，默认json
String returnMediaType = MediaType.APPLICATION_JSON;
// 如果接收到的请求头部没有具体格式信息，则返回格式为XML
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,
keyType, CurrentRequestVersion.get(), EurekaAccept.fromString(eurekaAccept), regions
);
// 返回不同的编码类型的数据，去缓存中取数据的方法基本一致
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();
}
CurrentRequestVersion.remove();
return response;
}
- responseCache.getGZIP 从缓存中读取数据
public byte[] getGZIP(Key key) {
Value payload = getValue(key, shouldUseReadOnlyResponseCache);
if (payload == null) {
return null;
}
return payload.getGzipped();
}
@VisibleForTesting
Value getValue(final Key key, boolean useReadOnlyCache) {
Value payload = null;
try {
if (useReadOnlyCache) {
// 如果开启了读缓存
// 先从读缓存中获取注册信息
final Value currentPayload = readOnlyCacheMap.get(key);
if (currentPayload != null) {
payload = currentPayload;
} else {
// 如果读缓存中没有，从写缓存中获取，然后同步到读缓存中！
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;
}
- 集成ribbon组件时，服务地址列表的获取
在pom中加上ribbon组件的依赖：
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
<version>2.2.3.RELEASE</version>
</dependency>
然后找到DynamicServerListLoadBalancer 这个类刷新服务列表的方法updateListOfServers
这时获取服务列表，会去调用eurekaClient 从注册中心获取：
@Override
public List<DiscoveryEnabledServer> getUpdatedListOfServers(){
return obtainServersViaDiscovery();
}
private List<DiscoveryEnabledServer> obtainServersViaDiscovery() {
List<DiscoveryEnabledServer> serverList = new ArrayList<DiscoveryEnabledServer>();
if (eurekaClientProvider == null || eurekaClientProvider.get() == null) {
logger.warn("EurekaClient has not been initialized yet, returning an empty list");
return new ArrayList<DiscoveryEnabledServer>();
}
EurekaClient eurekaClient = eurekaClientProvider.get();
if (vipAddresses!=null){
for (String vipAddress : vipAddresses.split(",")) {
// if targetRegion is null, it will be interpreted as the same region of client
List<InstanceInfo> listOfInstanceInfo = eurekaClient.getInstancesByVipAddress(vipAddress, isSecure, targetRegion);
for (InstanceInfo ii : listOfInstanceInfo) {
if (ii.getStatus().equals(InstanceStatus.UP)) {
if(shouldUseOverridePort){
if(logger.isDebugEnabled()){
logger.debug("Overriding port on client name: " + clientName + " to " + overridePort);
}
// copy is necessary since the InstanceInfo builder just uses the original reference,
// and we don't want to corrupt the global eureka copy of the object which may be
// used by other clients in our system
InstanceInfo copy = new InstanceInfo(ii);
if(isSecure){
ii = new InstanceInfo.Builder(copy).setSecurePort(overridePort).build();
}else{
ii = new InstanceInfo.Builder(copy).setPort(overridePort).build();
}
}
DiscoveryEnabledServer des = createServer(ii, isSecure, shouldUseIpAddr);
serverList.add(des);
}
}
if (serverList.size()>0 && prioritizeVipAddressBasedServers){
break; // if the current vipAddress has servers, we dont use subsequent vipAddress based servers
}
}
}
return serverList;
}
List listOfInstanceInfo = eurekaClient.getInstancesByVipAddress(vipAddress, isSecure, targetRegion);
看这个方法，它还是优先读取当前服务本地缓存中的服务列表：
- 心跳续约
还是在com.netflix.discovery.DiscoveryClient#initScheduledTasks 中，初始化了一个定时任务：
if (clientConfig.shouldRegisterWithEureka()) {
int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
logger.info("Starting heartbeat executor: " + "renew interval is: {}", renewalIntervalInSecs);
// Heartbeat timer
heartbeatTask = new TimedSupervisorTask(
"heartbeat",
scheduler,
heartbeatExecutor,
renewalIntervalInSecs,
TimeUnit.SECONDS,
expBackOffBound,
new HeartbeatThread()
);
scheduler.schedule(
heartbeatTask,
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");
}
续约的逻辑在HeartbeatThread中：
private class HeartbeatThread implements Runnable {
public void run() {
if (renew()) {
lastSuccessfulHeartbeatTimestamp = System.currentTimeMillis();
}
}
}
boolean renew() {
EurekaHttpResponse<InstanceInfo> httpResponse;
try {
httpResponse = eurekaTransport.registrationClient.sendHeartBeat(instanceInfo.getAppName(), instanceInfo.getId(), instanceInfo, null);
logger.debug(PREFIX + "{} - Heartbeat status: {}", appPathIdentifier, httpResponse.getStatusCode());
if (httpResponse.getStatusCode() == Status.NOT_FOUND.getStatusCode()) {
REREGISTER_COUNTER.increment();
logger.info(PREFIX + "{} - Re-registering apps/{}", appPathIdentifier, instanceInfo.getAppName());
long timestamp = instanceInfo.setIsDirtyWithTime();
boolean success = register();
if (success) {
instanceInfo.unsetIsDirty(timestamp);
}
return success;
}
// 心跳续约，拿到返回的状态码即可
return httpResponse.getStatusCode() == Status.OK.getStatusCode();
} catch (Throwable e) {
logger.error(PREFIX + "{} - was unable to send heartbeat!", appPathIdentifier, e);
return false;
}
}
- Eureka server服务延迟
服务上线的最大感知时间是90s,原因是， 读缓存readOnlyCache是30s同步一次，client每30s更新一次，ribbon每30s跟新一次serverList
修改默认时间：
responseCacheUpdateIntervalMS
registeryFetchIntervalSeconds
serviceListRefreshInterval