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本文主要研究下eureka server的RemoteRegionRegistry

PeerAwareInstanceRegistryImpl.getSortedApplications

eureka-core-1.8.8-sources.jar!/com/netflix/eureka/registry/PeerAwareInstanceRegistryImpl.java

/**     * Gets the list of all {@link Applications} from the registry in sorted     * lexical order of {@link Application#getName()}.     *     * @return the list of {@link Applications} in lexical order.     */    @Override    public List
    
      getSortedApplications() {        List
     
       apps = new ArrayList
      
       (getApplications().getRegisteredApplications());        Collections.sort(apps, APP_COMPARATOR);        return apps;    }
      
     
    

getApplications

/**     * Get all applications in this instance registry, falling back to other regions if allowed in the Eureka config.     *     * @return the list of all known applications     *     * @see com.netflix.discovery.shared.LookupService#getApplications()     */    public Applications getApplications() {        boolean disableTransparentFallback = serverConfig.disableTransparentFallbackToOtherRegion();        if (disableTransparentFallback) {            return getApplicationsFromLocalRegionOnly();        } else {            return getApplicationsFromAllRemoteRegions();  // Behavior of falling back to remote region can be disabled.        }    }

这里disableTransparentFallbackToOtherRegion默认为false，即会调用getApplicationsFromAllRemoteRegions

getApplicationsFromAllRemoteRegions

/**     * Returns applications including instances from all remote regions. 
     * Same as calling {@link #getApplicationsFromMultipleRegions(String[])} with a null argument.     */    public Applications getApplicationsFromAllRemoteRegions() {        return getApplicationsFromMultipleRegions(allKnownRemoteRegions);    }

注意这里传递了allKnownRemoteRegions参数调用了getApplicationsFromMultipleRegions

getApplicationsFromMultipleRegions

/**     * This method will return applications with instances from all passed remote regions as well as the current region.     * Thus, this gives a union view of instances from multiple regions. 
     * The application instances for which this union will be done can be restricted to the names returned by     * {@link EurekaServerConfig#getRemoteRegionAppWhitelist(String)} for every region. In case, there is no whitelist     * defined for a region, this method will also look for a global whitelist by passing null to the     * method {@link EurekaServerConfig#getRemoteRegionAppWhitelist(String)} 
     * If you are not selectively requesting for a remote region, use {@link #getApplicationsFromAllRemoteRegions()}     * or {@link #getApplicationsFromLocalRegionOnly()}     *     * @param remoteRegions The remote regions for which the instances are to be queried. The instances may be limited     *                      by a whitelist as explained above. If null or empty no remote regions are     *                      included.     *     * @return The applications with instances from the passed remote regions as well as local region. The instances     * from remote regions can be only for certain whitelisted apps as explained above.     */    public Applications getApplicationsFromMultipleRegions(String[] remoteRegions) {        boolean includeRemoteRegion = null != remoteRegions && remoteRegions.length != 0;        logger.debug("Fetching applications registry with remote regions: {}, Regions argument {}",                includeRemoteRegion, remoteRegions);        if (includeRemoteRegion) {            GET_ALL_WITH_REMOTE_REGIONS_CACHE_MISS.increment();        } else {            GET_ALL_CACHE_MISS.increment();        }        Applications apps = new Applications();        apps.setVersion(1L);        for (Entry
    
     >> entry : registry.entrySet()) {            Application app = null;            if (entry.getValue() != null) {                for (Entry
     
      > stringLeaseEntry : entry.getValue().entrySet()) {                    Lease
      
        lease = stringLeaseEntry.getValue();                    if (app == null) {                        app = new Application(lease.getHolder().getAppName());                    }                    app.addInstance(decorateInstanceInfo(lease));                }            }            if (app != null) {                apps.addApplication(app);            }        }        if (includeRemoteRegion) {            for (String remoteRegion : remoteRegions) {                RemoteRegionRegistry remoteRegistry = regionNameVSRemoteRegistry.get(remoteRegion);                if (null != remoteRegistry) {                    Applications remoteApps = remoteRegistry.getApplications();                    for (Application application : remoteApps.getRegisteredApplications()) {                        if (shouldFetchFromRemoteRegistry(application.getName(), remoteRegion)) {                            logger.info("Application {}  fetched from the remote region {}",                                    application.getName(), remoteRegion);                            Application appInstanceTillNow = apps.getRegisteredApplications(application.getName());                            if (appInstanceTillNow == null) {                                appInstanceTillNow = new Application(application.getName());                                apps.addApplication(appInstanceTillNow);                            }                            for (InstanceInfo instanceInfo : application.getInstances()) {                                appInstanceTillNow.addInstance(instanceInfo);                            }                        } else {                            logger.debug("Application {} not fetched from the remote region {} as there exists a "                                            + "whitelist and this app is not in the whitelist.",                                    application.getName(), remoteRegion);                        }                    }                } else {                    logger.warn("No remote registry available for the remote region {}", remoteRegion);                }            }        }        apps.setAppsHashCode(apps.getReconcileHashCode());        return apps;    }
      
     
    

• 这里会再对remoteRegions参数进行校验，确定是否includeRemoteRegion
• 首先从本地的registry获取applications
• 如果includeRemoteRegion为true的话，则在判断从regionNameVSRemoteRegistry获取指定region的RemoteRegionRegistry是否为null
• 另外还有shouldFetchFromRemoteRegistry(application.getName(), remoteRegion)判断，如果需要获取，则往apps结果集添加远程registry的注册信息

shouldFetchFromRemoteRegistry(application.getName(), remoteRegion)

private boolean shouldFetchFromRemoteRegistry(String appName, String remoteRegion) {        Set
    
      whiteList = serverConfig.getRemoteRegionAppWhitelist(remoteRegion);        if (null == whiteList) {            whiteList = serverConfig.getRemoteRegionAppWhitelist(null); // see global whitelist.        }        return null == whiteList || whiteList.contains(appName);    }
    

这里判断，如果对应region的AppWhitelist为null，则以全局的白名单为准，如果最后whiteList为null或者whiteList包含该app，则返回true，表示需要从远程获取

AbstractInstanceRegistry.initRemoteRegionRegistry

eureka-core-1.8.8-sources.jar!/com/netflix/eureka/registry/AbstractInstanceRegistry.java

protected void initRemoteRegionRegistry() throws MalformedURLException {        Map
    
      remoteRegionUrlsWithName = serverConfig.getRemoteRegionUrlsWithName();        if (!remoteRegionUrlsWithName.isEmpty()) {            allKnownRemoteRegions = new String[remoteRegionUrlsWithName.size()];            int remoteRegionArrayIndex = 0;            for (Map.Entry
     
       remoteRegionUrlWithName : remoteRegionUrlsWithName.entrySet()) {                RemoteRegionRegistry remoteRegionRegistry = new RemoteRegionRegistry(                        serverConfig,                        clientConfig,                        serverCodecs,                        remoteRegionUrlWithName.getKey(),                        new URL(remoteRegionUrlWithName.getValue()));                regionNameVSRemoteRegistry.put(remoteRegionUrlWithName.getKey(), remoteRegionRegistry);                allKnownRemoteRegions[remoteRegionArrayIndex++] = remoteRegionUrlWithName.getKey();            }        }        logger.info("Finished initializing remote region registries. All known remote regions: {}",                (Object) allKnownRemoteRegions);    }
     
    

eureka server初始化的时候，会调用initRemoteRegionRegistry方法，它读取remoteRegionUrlsWithName这个配置，然后新建RemoteRegionRegistry，放入regionNameVSRemoteRegistry中，另外也会记录regionName到allKnownRemoteRegions中。 这个方法初始化了前面几个类需要用的regionNameVSRemoteRegistry变量，及allKnownRemoteRegions变量

小结

eureka server的getApplications方法默认有个fallback，即会拉取remoteRegion的注册信息到本地，如果有配置remoteRegion的话。这个的好处就是，假设服务是分不同region部署，如果本地region的服务实例都挂了，但是本地eureka server还没有挂，那么它会fallback到远程region的服务实例，提高了可用性。

doc