Order
This article mainly studies the backup-registry-impl attribute of eurekclient.
Configuration
Configuration description
{
"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;
//......
}Configuration instance
eureka:
client:
fetch-registry: true
fetch-remote-regions-registry: east
backup-registry-impl: com.example.BackupServiceRegistryUse
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());
}Focus on the following paragraph
if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
fetchRegistryFromBackup();
}Here’s a fetchRegistry judgment.
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;
}False if getting an exception from the specified eureka server. Thus, when specifying that eureka server is not available, false will be returned and backup will be used to obtain
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;
}- As can be seen here, if the configuration file specifies eureka.client.backup-registry-impl, then backupRegistryInstance here is not null.
- It is also judged here that if eureka.client.fetch-remote-regions-registry is called if specified, backupegisterinstance.fetch registry (remoteregionstr.split (“,”) is called if not specified, backupegisterinstance.fetch registry ()
- Finally, the application information obtained by backup is filled into the local registration information table of localRegionApps
Backup-registry-impl instance
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;
}
}Summary
Eureka client provides a fallback, which allows the client to fallback to the specified backup-registry if it cannot access the specified eureka server at startup, and then fill the application information returned by backup-registry into localRegionApps, thus avoiding the problem that the client returns empty due to the failure of eureka server at startup.