服务发现
我们继续来研究服务的发现过程，就是客户端需要能够满足两个功能
- 在启动的时候获取指定服务提供者的地址列表
- Eureka server端地址发生变化时，需要动态感知
DiscoveryClient构造时进行查询
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,
Provider<BackupRegistry> backupRegistryProvider, EndpointRandomizer endpointRandomizer) {
if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
fetchRegistryFromBackup();
}
}
DiscoveryClient.fetchRegistry
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
{
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 {
getAndUpdateDelta(applications);
}
applications.setAppsHashCode(applications.getReconcileHashCode());
logTotalInstances();
} 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
onCacheRefreshed();
// Update remote status based on refreshed data held in the cache
updateInstanceRemoteStatus();
// registry was fetched successfully, so return true
return true;
}
定时任务每隔30s更新一次本地地址列表
在DiscoveryClient构造的时候，会初始化一些任务。其中有一个任务动态更新本地服务地址列表，叫 cacheRefreshTask 。这个任务最终执行的是CacheRefreshThread这个线程。它是一个周期性执行的任务，具体如下：
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);
}
}
TimedSupervisorTask
从整体上看，TimedSupervisorTask是固定间隔的周期性任务，一旦遇到超时就会将下一个周期的间隔时间调大，如果连续超时，那么每次间隔时间都会增大一倍，一直到达外部参数设定的上限为止，一旦新任务不再超时，间隔时间又会自动恢复为初始值。
public void run() {
Future<?> future = null;
try {
//使用Future，可以设定子线程的超时时间，这样当前线程就不用无限等待了
future = executor.submit(task);
threadPoolLevelGauge.set((long) executor.getActiveCount());
//指定等待子线程的最长时间
future.get(timeoutMillis, TimeUnit.MILLISECONDS); // block until done or timeout
//delay是个很有用的变量，后面会用到，这里记得每次执行任务成功都会将delay重置
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();
//任务线程超时的时候，就把delay变量翻倍，但不会超过外部调用时设定的最大延时时间
long newDelay = Math.min(maxDelay, currentDelay * 2);
//设置为最新的值，考虑到多线程，所以用了CAS
delay.compareAndSet(currentDelay, newDelay);
} catch (RejectedExecutionException e) {
//一旦线程池的阻塞队列中放满了待处理任务，触发了拒绝策略，就会将调度器停掉
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) {
//一旦出现未知的异常，就停掉调度器
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 {
//这里任务要么执行完毕，要么发生异常，都用cancel方法来清理任务；
if (future != null) {
future.cancel(true);
}
//只要调度器没有停止，就再指定等待时间之后在执行一次同样的任务
if (!scheduler.isShutdown()) {
//这里就是周期性任务的原因：只要没有停止调度器，就再创建一次性任务，执行时间时dealy的值，
//假设外部调用时传入的超时时间为30秒（构造方法的入参timeout），最大间隔时间为50秒(构造方法的入参expBackOffBound)
//如果最近一次任务没有超时，那么就在30秒后开始新任务，
//如果最近一次任务超时了，那么就在50秒后开始新任务（异常处理中有个乘以二的操作，乘以二后的60秒超过了最大间隔50秒）
scheduler.schedule(this, delay.get(), TimeUnit.MILLISECONDS);
}
}
}
CacheRefreshThread.refreshRegistry
这段代码主要两个逻辑
- 判断remoteRegions是否发生了变化
- 调用fetchRegistry获取本地服务地址缓存
void refreshRegistry() {
try {
boolean isFetchingRemoteRegionRegistries = isFetchingRemoteRegionRegistries();
boolean remoteRegionsModified = false;
// //如果部署在aws环境上，会判断最后一次远程区域更新的信息和当前远程区域信息进行比较，如果不相等，则更新
String latestRemoteRegions = clientConfig.fetchRegistryForRemoteRegions();
if (null != latestRemoteRegions) {
String currentRemoteRegions = remoteRegionsToFetch.get();
if (!latestRemoteRegions.equals(currentRemoteRegions)) {
//判断最后一次
}
boolean success = fetchRegistry(remoteRegionsModified);
if (success) {
registrySize = localRegionApps.get().size();
lastSuccessfulRegistryFetchTimestamp = System.currentTimeMillis();
}
//...
} catch (Throwable e) {
logger.error("Cannot fetch registry from server", e);
}
}
DisccoveryClient.fetchRegistry
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();
//判断多个条件，确定是否触发全量更新，如下任一个满足都会全量更新：
//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)
|| (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));
//调用全量更新
getAndStoreFullRegistry();
} else {
//调用增量更新
getAndUpdateDelta(applications);
}
//重新计算和设置一致性hash码
applications.setAppsHashCode(applications.getReconcileHashCode());
//日志打印所有应用的所有实例数之和
logTotalInstances();
} 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 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())
: 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)) {
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
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。
而对于增量请求，会调用ApplicationsResource.getContainerDifferential。
ApplicationsResource.getContainers
@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.
// EurekaServer无法提供服务，返回403
if (!registry.shouldAllowAccess(isRemoteRegionRequested)) {
return Response.status(Status.FORBIDDEN).build();
}
CurrentRequestVersion.set(Version.toEnum(version));
// 设置返回数据格式，默认JSON
KeyType keyType = Key.KeyType.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
);
Response response;
// 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
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();
}
Value getValue(final Key key, boolean useReadOnlyCache) {
Value payload = null;
try {
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;
}