序
本文主要研究一下eureka client的backup-registry-impl屬性
配置
配置說明
{
"sourceType": "org.springframework.cloud.netflix.eureka.EurekaClientConfigBean",
"name": "eureka.client.fetch-remote-regions-registry",
"description": "Comma separated list of regions for which the eureka registry information will be\n fetched. It is mandatory to define the availability zones for each of these regions\n as returned by availabilityZones. Failing to do so, will result in failure of\n discovery client startup.",
"type": "java.lang.String"
}EurekaClientConfigBean
spring-cloud-netflix-eureka-client-2.0.0.RC1-sources.jar!/org/springframework/cloud/netflix/eureka/EurekaClientConfigBean.java
@ConfigurationProperties(EurekaClientConfigBean.PREFIX)
public class EurekaClientConfigBean implements EurekaClientConfig {
//......
/**
* Comma separated list of regions for which the eureka registry information will be
* fetched. It is mandatory to define the availability zones for each of these regions
* as returned by availabilityZones. Failing to do so, will result in failure of
* discovery client startup.
*
*/
private String fetchRemoteRegionsRegistry;
//......
}配置實例
eureka:
client:
fetch-registry: true
fetch-remote-regions-registry: east
backup-registry-impl: com.example.BackupServiceRegistry使用
eureka-client-1.8.8-sources.jar!/com/netflix/discovery/DiscoveryClient.java
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,
Provider<BackupRegistry> backupRegistryProvider) {
if (args != null) {
this.healthCheckHandlerProvider = args.healthCheckHandlerProvider;
this.healthCheckCallbackProvider = args.healthCheckCallbackProvider;
this.eventListeners.addAll(args.getEventListeners());
this.preRegistrationHandler = args.preRegistrationHandler;
} else {
this.healthCheckCallbackProvider = null;
this.healthCheckHandlerProvider = null;
this.preRegistrationHandler = null;
}
this.applicationInfoManager = applicationInfoManager;
InstanceInfo myInfo = applicationInfoManager.getInfo();
clientConfig = config;
staticClientConfig = clientConfig;
transportConfig = config.getTransportConfig();
instanceInfo = myInfo;
if (myInfo != null) {
appPathIdentifier = instanceInfo.getAppName() + "/" + instanceInfo.getId();
} else {
logger.warn("Setting instanceInfo to a passed in null value");
}
this.backupRegistryProvider = backupRegistryProvider;
this.urlRandomizer = new EndpointUtils.InstanceInfoBasedUrlRandomizer(instanceInfo);
localRegionApps.set(new Applications());
fetchRegistryGeneration = new AtomicLong(0);
remoteRegionsToFetch = new AtomicReference<String>(clientConfig.fetchRegistryForRemoteRegions());
remoteRegionsRef = new AtomicReference<>(remoteRegionsToFetch.get() == null ? null : remoteRegionsToFetch.get().split(","));
if (config.shouldFetchRegistry()) {
this.registryStalenessMonitor = new ThresholdLevelsMetric(this, METRIC_REGISTRY_PREFIX + "lastUpdateSec_", new long[]{15L, 30L, 60L, 120L, 240L, 480L});
} else {
this.registryStalenessMonitor = ThresholdLevelsMetric.NO_OP_METRIC;
}
if (config.shouldRegisterWithEureka()) {
this.heartbeatStalenessMonitor = new ThresholdLevelsMetric(this, METRIC_REGISTRATION_PREFIX + "lastHeartbeatSec_", new long[]{15L, 30L, 60L, 120L, 240L, 480L});
} else {
this.heartbeatStalenessMonitor = ThresholdLevelsMetric.NO_OP_METRIC;
}
logger.info("Initializing Eureka in region {}", clientConfig.getRegion());
if (!config.shouldRegisterWithEureka() && !config.shouldFetchRegistry()) {
logger.info("Client configured to neither register nor query for data.");
scheduler = null;
heartbeatExecutor = null;
cacheRefreshExecutor = null;
eurekaTransport = null;
instanceRegionChecker = new InstanceRegionChecker(new PropertyBasedAzToRegionMapper(config), clientConfig.getRegion());
// This is a bit of hack to allow for existing code using DiscoveryManager.getInstance()
// to work with DI'd DiscoveryClient
DiscoveryManager.getInstance().setDiscoveryClient(this);
DiscoveryManager.getInstance().setEurekaClientConfig(config);
initTimestampMs = System.currentTimeMillis();
logger.info("Discovery Client initialized at timestamp {} with initial instances count: {}",
initTimestampMs, this.getApplications().size());
return; // no need to setup up an network tasks and we are done
}
try {
// default size of 2 - 1 each for heartbeat and cacheRefresh
scheduler = Executors.newScheduledThreadPool(2,
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-%d")
.setDaemon(true)
.build());
heartbeatExecutor = new ThreadPoolExecutor(
1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
.setDaemon(true)
.build()
); // use direct handoff
cacheRefreshExecutor = new ThreadPoolExecutor(
1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d")
.setDaemon(true)
.build()
); // use direct handoff
eurekaTransport = new EurekaTransport();
scheduleServerEndpointTask(eurekaTransport, args);
AzToRegionMapper azToRegionMapper;
if (clientConfig.shouldUseDnsForFetchingServiceUrls()) {
azToRegionMapper = new DNSBasedAzToRegionMapper(clientConfig);
} else {
azToRegionMapper = new PropertyBasedAzToRegionMapper(clientConfig);
}
if (null != remoteRegionsToFetch.get()) {
azToRegionMapper.setRegionsToFetch(remoteRegionsToFetch.get().split(","));
}
instanceRegionChecker = new InstanceRegionChecker(azToRegionMapper, clientConfig.getRegion());
} catch (Throwable e) {
throw new RuntimeException("Failed to initialize DiscoveryClient!", e);
}
if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
fetchRegistryFromBackup();
}
// call and execute the pre registration handler before all background tasks (inc registration) is started
if (this.preRegistrationHandler != null) {
this.preRegistrationHandler.beforeRegistration();
}
if (clientConfig.shouldRegisterWithEureka() && clientConfig.shouldEnforceRegistrationAtInit()) {
try {
if (!register() ) {
throw new IllegalStateException("Registration error at startup. Invalid server response.");
}
} catch (Throwable th) {
logger.error("Registration error at startup: {}", th.getMessage());
throw new IllegalStateException(th);
}
}
// finally, init the schedule tasks (e.g. cluster resolvers, heartbeat, instanceInfo replicator, fetch
initScheduledTasks();
try {
Monitors.registerObject(this);
} catch (Throwable e) {
logger.warn("Cannot register timers", e);
}
// This is a bit of hack to allow for existing code using DiscoveryManager.getInstance()
// to work with DI'd DiscoveryClient
DiscoveryManager.getInstance().setDiscoveryClient(this);
DiscoveryManager.getInstance().setEurekaClientConfig(config);
initTimestampMs = System.currentTimeMillis();
logger.info("Discovery Client initialized at timestamp {} with initial instances count: {}",
initTimestampMs, this.getApplications().size());
}重點看下面這段
if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
fetchRegistryFromBackup();
}這裏有個fetchRegistry判斷
fetchRegistry
/**
* 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;
}如果從指定的eureka server獲取信息報異常，則返回false。由此可見，在指定eureka server不可用的時候，會返回false，然後使用backup來獲取
fetchRegistryFromBackup
/**
* Fetch the registry information from back up registry if all eureka server
* urls are unreachable.
*/
private void fetchRegistryFromBackup() {
try {
@SuppressWarnings("deprecation")
BackupRegistry backupRegistryInstance = newBackupRegistryInstance();
if (null == backupRegistryInstance) { // backward compatibility with the old protected method, in case it is being used.
backupRegistryInstance = backupRegistryProvider.get();
}
if (null != backupRegistryInstance) {
Applications apps = null;
if (isFetchingRemoteRegionRegistries()) {
String remoteRegionsStr = remoteRegionsToFetch.get();
if (null != remoteRegionsStr) {
apps = backupRegistryInstance.fetchRegistry(remoteRegionsStr.split(","));
}
} else {
apps = backupRegistryInstance.fetchRegistry();
}
if (apps != null) {
final Applications applications = this.filterAndShuffle(apps);
applications.setAppsHashCode(applications.getReconcileHashCode());
localRegionApps.set(applications);
logTotalInstances();
logger.info("Fetched registry successfully from the backup");
}
} else {
logger.warn("No backup registry instance defined & unable to find any discovery servers.");
}
} catch (Throwable e) {
logger.warn("Cannot fetch applications from apps although backup registry was specified", e);
}
}
private boolean isFetchingRemoteRegionRegistries() {
return null != remoteRegionsToFetch.get();
}
/**
* @deprecated Use injection to provide {@link BackupRegistry} implementation.
*/
@Deprecated
@Nullable
protected BackupRegistry newBackupRegistryInstance()
throws ClassNotFoundException, IllegalAccessException, InstantiationException {
return null;
}- 這裏可以看到，如果配置文件指定了eureka.client.backup-registry-impl則這裏backupRegistryInstance不爲null。
- 這裏還判斷，如果eureka.client.fetch-remote-regions-registry，如果有指定則調用backupRegistryInstance.fetchRegistry(remoteRegionsStr.split(“,”))，沒有指定則調用backupRegistryInstance.fetchRegistry()
- 最後將backup獲取的應用信息填充到localRegionApps本地註冊信息表裏頭
backup-registry-impl實例
public class BackupServiceRegistry implements BackupRegistry {
private static final Logger LOGGER = LoggerFactory.getLogger(BackupServiceRegistry.class);
private Map<String, Applications> remoteRegionVsApps = new HashMap<String, Applications>();
private Applications localRegionApps;
@Override
public Applications fetchRegistry() {
LOGGER.info("fetchRegistry() called");
if (null == localRegionApps) {
return new Applications();
}
return localRegionApps;
}
@Override
public Applications fetchRegistry(String[] includeRemoteRegions) {
LOGGER.info("fetchRegistry(String[] includeRemoteRegions) called");
Applications toReturn = new Applications();
for (Application application : localRegionApps.getRegisteredApplications()) {
toReturn.addApplication(application);
}
for (String region : includeRemoteRegions) {
Applications applications = remoteRegionVsApps.get(region);
if (null != applications) {
for (Application application : applications.getRegisteredApplications()) {
toReturn.addApplication(application);
}
}
}
return toReturn;
}
public Applications getLocalRegionApps() {
return localRegionApps;
}
public Map<String, Applications> getRemoteRegionVsApps() {
return remoteRegionVsApps;
}
public void setRemoteRegionVsApps(Map<String, Applications> remoteRegionVsApps) {
this.remoteRegionVsApps = remoteRegionVsApps;
}
public void setLocalRegionApps(Applications localRegionApps) {
this.localRegionApps = localRegionApps;
}
}小結
eureka client提供了一個fallback，允許在啓動的時候，訪問不到指定的eureka server的話，會fallback到指定的backup-registry，然後將backup-registry返回的應用信息填充到localRegionApps中，這樣來避免client在啓動時因爲eureka server故障原因導致返回空的問題。
doc
- Add ability to retrieve instances from any remote region #29