深入理解Eureka - Eureka Client获取注册信息机制


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(
                    new TimedSupervisorTask(
                            "cacheRefresh",
                            scheduler,
                            cacheRefreshExecutor,
                            registryFetchIntervalSeconds,
                            TimeUnit.SECONDS,
                            expBackOffBound,
                            new CacheRefreshThread()
                    ),
                    registryFetchIntervalSeconds, TimeUnit.SECONDS);
        }

Eureka Client提供了两种获取注册信息的模式

  1. 全量获取
  2. 增量获取

Eureka Client全量获取注册信息

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

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.
     */
    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");
        }
    }

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
    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.
        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;
        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
        );

        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
     */
    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();
        }

        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 {
                    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}.
     *
     * <p>
     * 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
     * <em>Registrations,Cancels,Status Changes and Expirations</em>. Normally
     * the changes to the registry are infrequent and hence getting just the
     * delta will be much more efficient than getting the complete registry.
     * </p>
     *
     * <p>
     * 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.
     * <p>
     *
     * @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
    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
        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;
        }

        Key cacheKey = new Key(Key.EntityType.Application,
                ResponseCacheImpl.ALL_APPS_DELTA,
                keyType, CurrentRequestVersion.get(), EurekaAccept.fromString(eurekaAccept), regions
        );

        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();
        }
    }

备注:Register、renew、cancel、evict最终都会更新recnetlyChangedQueue队列,Eureka Client获取的增量信息都是从这个队列中获取的。

 

Spring Cloud实战项目Jbone地址

github地址:https://github.com/417511458/jbone

码云地址:https://gitee.com/majunwei2017/jbone

马军伟
关于作者 马军伟
写的不错,支持一下

先给自己定个小目标,日更一新。