深入理解Eureka

深入理解Eureka - Eureka Client获取注册信息机

Eureka Client提供了定时获取注册信息的机制。Eureka Client获取注册信息的所有逻辑都在DiscoveryClient类里。

Eureka在初始化的时候根据获取注册信息的开关（默认开启）来决定是否初始化获取注册信息定时任务（默认30S同步一次）：

if(clientConfig.shouldFetchRegistry()){
// registry cache refresh timer
int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
scheduler.schedule(
newTimedSupervisorTask(
"cacheRefresh",
scheduler,
cacheRefreshExecutor,
registryFetchIntervalSeconds,
TimeUnit.SECONDS,
expBackOffBound,
newCacheRefreshThread()
),
registryFetchIntervalSeconds,TimeUnit.SECONDS);
}

Eureka Client提供了两种获取注册信息的模式

全量获取
增量获取

Eureka Client全量获取注册信息

/**
* Fetches the registry information.
*
*
* This method tries to get only deltas after the first fetch unless there
* is an issue in reconciling eureka server and client registry information.
*
*
* @param forceFullRegistryFetch Forces a full registry fetch.
*
* @return true if the registry was fetched
*/
privateboolean 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);
returnfalse;
}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
returntrue;
}

全量获取的条件

1、配置禁用了增量获取

2、首次请求（当前applications为空 | 当前获取到的application为0）

3、如果增量同步失败，还会强制全量同步

全量同步流程

全量同步时，通过访问Eureka Server的接口来获取全部服务信息

/**
* Gets the full registry information from the eureka server and stores it locally.
* When applying the full registry, the following flow is observed:
*
* if (update generation have not advanced (due to another thread))
* atomically set the registry to the new registry
* fi
*
* @return the full registry information.
* @throws Throwable
* on error.
*/
privatevoid getAndStoreFullRegistry()throwsThrowable{
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");
}elseif(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");
}
}

Eureka Server的com.netflix.eureka.resources.ApplicationsResource#Containers接收到请求后将服务信息返回。

/**
* Get information about all {@link com.netflix.discovery.shared.Applications}.
*
* @param version the version of the request.
* @param acceptHeader the accept header to indicate whether to serve JSON or XML data.
* @param acceptEncoding the accept header to indicate whether to serve compressed or uncompressed data.
* @param eurekaAccept an eureka accept extension, see {@link com.netflix.appinfo.EurekaAccept}
* @param uriInfo the {@link java.net.URI} information of the request made.
* @param regionsStr A comma separated list of remote regions from which the instances will also be returned.
* The applications returned from the remote region can be limited to the applications
* returned by {@link EurekaServerConfig#getRemoteRegionAppWhitelist(String)}
*
* @return a response containing information about all {@link com.netflix.discovery.shared.Applications}
* from the {@link AbstractInstanceRegistry}.
*/
@GET
publicResponse getContainers(@PathParam("version")String version,
@HeaderParam(HEADER_ACCEPT)String acceptHeader,
@HeaderParam(HEADER_ACCEPT_ENCODING)String acceptEncoding,
@HeaderParam(EurekaAccept.HTTP_X_EUREKA_ACCEPT)String eurekaAccept,
@ContextUriInfo 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.
if(!registry.shouldAllowAccess(isRemoteRegionRequested)){
returnResponse.status(Status.FORBIDDEN).build();
}
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;
}
Key cacheKey =newKey(Key.EntityType.Application,
ResponseCacheImpl.ALL_APPS,
keyType,CurrentRequestVersion.get(),EurekaAccept.fromString(eurekaAccept), regions
);
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;
}

Eureka Client增量获取注册信息

增量获取条件

只有开启了增量获取的开关，且非首次获取时，才进行增量的获取。

增量获取流程

增量获取时，通过访问Eureka Server的增量接口，来获取增量的服务信息（注意增量同步失败后会全量同步）

/**
* Get the delta registry information from the eureka server and update it locally.
* When applying the delta, the following flow is observed:
*
* if (update generation have not advanced (due to another thread))
* atomically try to: update application with the delta and get reconcileHashCode
* abort entire processing otherwise
* do reconciliation if reconcileHashCode clash
* fi
*
* @return the client response
* @throws Throwable on error
*/
privatevoid getAndUpdateDelta(Applications applications)throwsThrowable{
long currentUpdateGeneration = fetchRegistryGeneration.get();
Applications delta =null;
EurekaHttpResponse<Applications> httpResponse = eurekaTransport.queryClient.getDelta(remoteRegionsRef.get());
if(httpResponse.getStatusCode()==Status.OK.getStatusCode()){
delta = httpResponse.getEntity();
}
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();
}elseif(fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration +1)){
logger.debug("Got delta update with apps hashcode {}", delta.getAppsHashCode());
String reconcileHashCode ="";
if(fetchRegistryUpdateLock.tryLock()){
try{
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
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());
}
}

然后Eureka Server的接口接收到增量请求后，将增量服务返回给Eureka Client

/**
* Get information about all delta changes in {@link com.netflix.discovery.shared.Applications}.
*
*
* The delta changes represent the registry information change for a period
* as configured by
* {@link EurekaServerConfig#getRetentionTimeInMSInDeltaQueue()}. The
* changes that can happen in a registry include
* Registrations,Cancels,Status Changes and Expirations. Normally
* the changes to the registry are infrequent and hence getting just the
* delta will be much more efficient than getting the complete registry.
*
*
*
* Since the delta information is cached over a period of time, the requests
* may return the same data multiple times within the window configured by
* {@link EurekaServerConfig#getRetentionTimeInMSInDeltaQueue()}.The clients
* are expected to handle this duplicate information.
*
*
* @param version the version of the request.
* @param acceptHeader the accept header to indicate whether to serve JSON or XML data.
* @param acceptEncoding the accept header to indicate whether to serve compressed or uncompressed data.
* @param eurekaAccept an eureka accept extension, see {@link com.netflix.appinfo.EurekaAccept}
* @param uriInfo the {@link java.net.URI} information of the request made.
* @return response containing the delta information of the
* {@link AbstractInstanceRegistry}.
*/
@Path("delta")
@GET
publicResponse getContainerDifferential(
@PathParam("version")String version,
@HeaderParam(HEADER_ACCEPT)String acceptHeader,
@HeaderParam(HEADER_ACCEPT_ENCODING)String acceptEncoding,
@HeaderParam(EurekaAccept.HTTP_X_EUREKA_ACCEPT)String eurekaAccept,
@ContextUriInfo 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
if((serverConfig.shouldDisableDelta())||(!registry.shouldAllowAccess(isRemoteRegionRequested))){
returnResponse.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;
}
Key cacheKey =newKey(Key.EntityType.Application,
ResponseCacheImpl.ALL_APPS_DELTA,
keyType,CurrentRequestVersion.get(),EurekaAccept.fromString(eurekaAccept), regions
);
if(acceptEncoding !=null
&& acceptEncoding.contains(HEADER_GZIP_VALUE)){
returnResponse.ok(responseCache.getGZIP(cacheKey))
.header(HEADER_CONTENT_ENCODING, HEADER_GZIP_VALUE)
.header(HEADER_CONTENT_TYPE, returnMediaType)
.build();
}else{
returnResponse.ok(responseCache.get(cacheKey))
.build();
}
}