上一篇我们讨论了关于周期性任务的一些应用等，本篇文章我们来探究一下这些内容：周期性刷新注册表？全量拉取注册表还是增量拉取注册表、更新本地缓存？服务发现的入口、获取本地服务列表？
同样是在Spring容器初始化的过程中初始化的，基于SpringBoot自动装配集成。上一节也讲了一部分，这里补充：
@Singleton
public class DiscoveryClient implements EurekaClient {
....省略n行代码......
private final ScheduledExecutorService scheduler;
// additional executors for supervised subtasks监督子任务的附加执行器
private final ThreadPoolExecutor heartbeatExecutor;
private final ThreadPoolExecutor cacheRefreshExecutor;
private TimedSupervisorTask cacheRefreshTask;
private TimedSupervisorTask heartbeatTask;
....省略n行代码......
// Spring容器初始化时候调用
public DiscoveryClient(ApplicationInfoManager applicationInfoManager,
final EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args) {
// 调用下面重载方法
this(applicationInfoManager, config, args, ResolverUtils::randomize);
}
public DiscoveryClient(ApplicationInfoManager applicationInfoManager,
final EurekaClientConfig config,
AbstractDiscoveryClientOptionalArgs args, EndpointRandomizer randomizer) {
this(applicationInfoManager, config, args, new Provider<BackupRegistry>() {
....省略n行代码......
}
@Inject
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config,
AbstractDiscoveryClientOptionalArgs args,
Provider<BackupRegistry> backupRegistryProvider, EndpointRandomizer endpointRandomizer) {
try {
// default size of 2 - 1 each for heartbeat and cacheRefresh心跳和缓存刷新的默认大小分别为2-1
scheduler = Executors.newScheduledThreadPool(2,
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-%d")
.setDaemon(true)
.build());
// 心跳执行者
heartbeatExecutor = new ThreadPoolExecutor(
1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
.setDaemon(true)
.build()
); // use direct handoff
// 缓存刷新执行者
cacheRefreshExecutor = new ThreadPoolExecutor(
1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d")
.setDaemon(true)
.build()
); // use direct handoff
// 初始化通信封装类
eurekaTransport = new EurekaTransport();
....省略n行代码......
} catch (Throwable e) {
throw new RuntimeException("Failed to initialize DiscoveryClient!", e);
}
// 默认true，可更改配置不建议
if (clientConfig.shouldFetchRegistry()) {
try {// 初始化注册表
boolean primaryFetchRegistryResult = fetchRegistry(false);
// 下面主要打印失败日志，初始化时控制台可见是处理成功的
if (!primaryFetchRegistryResult) {
// 从主服务器初始注册表提取失败
logger.info("Initial registry fetch from primary servers failed");
}
boolean backupFetchRegistryResult = true;
if (!primaryFetchRegistryResult && !fetchRegistryFromBackup()) {
// 如果所有的eureka服务器网址都无法访问，从备份注册表中获取注册表信息也失败。
backupFetchRegistryResult = false;
// 从备份服务器初始注册表提取失败
logger.info("Initial registry fetch from backup servers failed");
}
if (!primaryFetchRegistryResult && !backupFetchRegistryResult && clientConfig.shouldEnforceFetchRegistryAtInit()) {
// 在启动时获取注册表错误。初始获取失败。
throw new IllegalStateException("Fetch registry error at startup. Initial fetch failed.");
}
} catch (Throwable th) {
logger.error("Fetch registry error at startup: {}", th.getMessage());
throw new IllegalStateException(th);
}
}
....省略n行代码......
// 最后，初始化调度任务(例如，集群解析器、 heartbeat、 instanceInfo replicator、 fetch
initScheduledTasks();
....省略n行代码......
}主要逻辑：
大部分逻辑在前面的章节已经分析，TimedSupervisorTask跟发送心跳服务续约逻辑是一样的，这里补充刷新本地服务列表任务。
private void initScheduledTasks() {
// 默认true，可更改配置不建议
if (clientConfig.shouldFetchRegistry()) {
// registry cache refresh timer注册表缓存刷新计时器
// 默认30
int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
cacheRefreshTask = new TimedSupervisorTask(
"cacheRefresh",
scheduler,
cacheRefreshExecutor,
registryFetchIntervalSeconds,
TimeUnit.SECONDS,
expBackOffBound,
new CacheRefreshThread()
);
scheduler.schedule(
cacheRefreshTask,
registryFetchIntervalSeconds, TimeUnit.SECONDS);
}
if (clientConfig.shouldRegisterWithEureka()) {
/* LeaseInfo：
public static final int DEFAULT_LEASE_RENEWAL_INTERVAL = 30;
// Client settings
private int renewalIntervalInSecs = DEFAULT_LEASE_RENEWAL_INTERVAL;
*/
// 默认30
int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
logger.info("Starting heartbeat executor: " + "renew interval is: {}", renewalIntervalInSecs);
// Heartbeat timer心跳任务
heartbeatTask = new TimedSupervisorTask(
"heartbeat",
scheduler,
heartbeatExecutor,
renewalIntervalInSecs,
TimeUnit.SECONDS,
expBackOffBound,
new HeartbeatThread()
);
// 默认的情况下会每隔30秒向注册中心 (eureka.instance.lease-renewal-interval-in-seconds)发送一次心跳来进行服务续约
scheduler.schedule(
heartbeatTask,
renewalIntervalInSecs, TimeUnit.SECONDS);
// InstanceInfo replicator实例信息复制任务
instanceInfoReplicator = new InstanceInfoReplicator(
this,
instanceInfo,
clientConfig.getInstanceInfoReplicationIntervalSeconds(),
2); // burstSize
// 状态变更监听者
statusChangeListener = new ApplicationInfoManager.StatusChangeListener() {
@Override
public String getId() {
return "statusChangeListener";
}
@Override
public void notify(StatusChangeEvent statusChangeEvent) {
// Saw local status change event StatusChangeEvent [timestamp=1668595102513, current=UP, previous=STARTING]
logger.info("Saw local status change event {}", statusChangeEvent);
instanceInfoReplicator.onDemandUpdate();
}
};
// 初始化状态变更监听者
if (clientConfig.shouldOnDemandUpdateStatusChange()) {
applicationInfoManager.registerStatusChangeListener(statusChangeListener);
}
// 3.2 定时刷新服务实例信息和检查应用状态的变化，在服务实例信息发生改变的情况下向server重新发起注册
instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
} else {
logger.info("Not registering with Eureka server per configuration");
}
}主要逻辑：
默认需要刷新注册表，要达到服务高可用。
1）clientConfig.getRegistryFetchIntervalSeconds()获取注册表刷新时间，默认30秒，可在配置文件更改；
2）初始化cacheRefreshTask为TimedSupervisorTask类型，跟心跳任务一样处理逻辑，我们这节就只分析CacheRefreshThread刷新缓存逻辑，见3
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如果 delta 被禁用或者是第一次，那么获取所有的应用程序
Applications applications = getApplications();
// shouldDisableDelta默认false
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
{
// 第一次
logger.info("Disable delta property false: {}", clientConfig.shouldDisableDelta());
logger.info("Single vip registry refresh property null: {}", clientConfig.getRegistryRefreshSingleVipAddress());
logger.info("Force full registry fetch false: {}", forceFullRegistryFetch);
logger.info("Application is null false: {}", (applications == null));
logger.info("Registered Applications size is zero true: {}",
(applications.getRegisteredApplications().size() == 0));
logger.info("Application version is -1true: {}", (applications.getVersion() == -1));
// 全量拉取
getAndStoreFullRegistry();
} else {
// 增量拉取
getAndUpdateDelta(applications);
}
applications.setAppsHashCode(applications.getReconcileHashCode());
logTotalInstances();
} catch (Throwable e) {
logger.info(PREFIX + "{} - was unable to refresh its cache! This periodic background refresh will be retried in {} seconds. status = {} stacktrace = {}",
appPathIdentifier, clientConfig.getRegistryFetchIntervalSeconds(), e.getMessage(), ExceptionUtils.getStackTrace(e));
return false;
} finally {
if (tracer != null) {
tracer.stop();
}
}
// Notify about cache refresh before updating the instance remote status
// 在更新实例远程状态之前通知缓存刷新
onCacheRefreshed();
// Update remote status based on refreshed data held in the cache
// 根据缓存中保存的刷新数据更新远程状态
updateInstanceRemoteStatus();
// registry was fetched successfully, so return true
return true;
}主要逻辑：
private void getAndStoreFullRegistry() throws Throwable {
long currentUpdateGeneration = fetchRegistryGeneration.get();
// 从 eureka 服务器上获取所有实例注册信息
logger.info("Getting all instance registry info from the eureka server");
Applications apps = null;
// RegistryRefreshSingleVipAddress默认空
EurekaHttpResponse<Applications> httpResponse = clientConfig.getRegistryRefreshSingleVipAddress() == null
? eurekaTransport.queryClient.getApplications(remoteRegionsRef.get())
: eurekaTransport.queryClient.getVip(clientConfig.getRegistryRefreshSingleVipAddress(), remoteRegionsRef.get());
// 响应成功获取应用
if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
apps = httpResponse.getEntity();
}
// 200
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)) {
// 缓存到本地
localRegionApps.set(this.filterAndShuffle(apps));
// 如：UP_1_
logger.debug("Got full registry with apps hashcode {}", apps.getAppsHashCode());
} else {
logger.warn("Not updating applications as another thread is updating it already");
}
}主要逻辑：
class CacheRefreshThread implements Runnable {
@Override
public void run() {
refreshRegistry();
}
}
@VisibleForTesting
void refreshRegistry() {
try {
boolean isFetchingRemoteRegionRegistries = isFetchingRemoteRegionRegistries();
boolean remoteRegionsModified = false;
// This makes sure that a dynamic change to remote regions to fetch is honored.
// 这可以确保对要获取的远程区域的动态更改得到遵守。
// 默认null
String latestRemoteRegions = clientConfig.fetchRegistryForRemoteRegions();
if (null != latestRemoteRegions) {
String currentRemoteRegions = remoteRegionsToFetch.get();
if (!latestRemoteRegions.equals(currentRemoteRegions)) {
// Both remoteRegionsToFetch and AzToRegionMapper.regionsToFetch need to be in sync
// RemoteRegionsToFetch 和 AzToRegionMapper.regionsToFetch 都需要同步
synchronized (instanceRegionChecker.getAzToRegionMapper()) {
// CAS
if (remoteRegionsToFetch.compareAndSet(currentRemoteRegions, latestRemoteRegions)) {
String[] remoteRegions = latestRemoteRegions.split(",");
remoteRegionsRef.set(remoteRegions);
instanceRegionChecker.getAzToRegionMapper().setRegionsToFetch(remoteRegions);
remoteRegionsModified = true;
} else {
// 并发获取修改的远程区域,忽略从{}到{}的更改
logger.info("Remote regions to fetch modified concurrently," +
" ignoring change from {} to {}", currentRemoteRegions, latestRemoteRegions);
}
}
} else {
// Just refresh mapping to reflect any DNS/Property change
// 只需刷新映射以反映任何 DNS/属性更改
instanceRegionChecker.getAzToRegionMapper().refreshMapping();
}
}
// 刷新注册表
boolean success = fetchRegistry(remoteRegionsModified);
if (success) {
registrySize = localRegionApps.get().size();
lastSuccessfulRegistryFetchTimestamp = System.currentTimeMillis();
}
if (logger.isDebugEnabled()) {
StringBuilder allAppsHashCodes = new StringBuilder();
allAppsHashCodes.append("Local region apps hashcode: ");
allAppsHashCodes.append(localRegionApps.get().getAppsHashCode());
allAppsHashCodes.append(", is fetching remote regions? ");
allAppsHashCodes.append(isFetchingRemoteRegionRegistries);
for (Map.Entry<String, Applications> entry : remoteRegionVsApps.entrySet()) {
allAppsHashCodes.append(", Remote region: ");
allAppsHashCodes.append(entry.getKey());
allAppsHashCodes.append(" , apps hashcode: ");
allAppsHashCodes.append(entry.getValue().getAppsHashCode());
}
logger.debug("Completed cache refresh task for discovery. All Apps hash code is {} ",
allAppsHashCodes);
}
} catch (Throwable e) {
logger.error("Cannot fetch registry from server", e);
}
}CacheRefreshThread 实现了Runnable接口，但是run()中任务逻辑封装了出去，在refreshRegistry()中处理。在2中分析了初始化时已经使用全量拉取注册表并缓存应用到本地localRegionApps，那么这里使用延迟任务处理的话就会执行增量拉取逻辑了，在下面4分析
private void getAndUpdateDelta(Applications applications) throws Throwable {
long currentUpdateGeneration = fetchRegistryGeneration.get();
Applications delta = null;
// 增量查询获取
EurekaHttpResponse<Applications> httpResponse = eurekaTransport.queryClient.getDelta(remoteRegionsRef.get());
// 响应成功
if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
delta = httpResponse.getEntity();
}
if (delta == null) {
// 服务器不允许应用delta修订，因为它不安全。因此得到了完整的登记表，即转换为全量拉取
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)) {
// CAS成功
logger.debug("Got delta update with apps hashcode {}", delta.getAppsHashCode());
String reconcileHashCode = "";
if (fetchRegistryUpdateLock.tryLock()) {
// 加锁成功
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出于某种原因，数量有所不同
if (!reconcileHashCode.equals(delta.getAppsHashCode()) || clientConfig.shouldLogDeltaDiff()) {
reconcileAndLogDifference(delta, reconcileHashCode); // this makes a remoteCall这个可以远程呼叫
}
} 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());
}
}主要逻辑：
private void updateDelta(Applications delta) {
int deltaCount = 0;
for (Application app : delta.getRegisteredApplications()) {
for (InstanceInfo instance : app.getInstances()) {
// 从本地获取，以便更新
Applications applications = getApplications();
String instanceRegion = instanceRegionChecker.getInstanceRegion(instance);
if (!instanceRegionChecker.isLocalRegion(instanceRegion)) {
Applications remoteApps = remoteRegionVsApps.get(instanceRegion);
if (null == remoteApps) {
remoteApps = new Applications();
remoteRegionVsApps.put(instanceRegion, remoteApps);
}
applications = remoteApps;
}
++deltaCount;
if (ActionType.ADDED.equals(instance.getActionType())) {
Application existingApp = applications.getRegisteredApplications(instance.getAppName());
if (existingApp == null) {
applications.addApplication(app);
}
// 将实例{}添加到区域{}中的现有应用程序
// ceam-config:8888,ceam-auth:8005,region null
logger.debug("Added instance {} to the existing apps in region {}", instance.getId(), instanceRegion);
// 即添加到Application的instancesMap
applications.getRegisteredApplications(instance.getAppName()).addInstance(instance);
} else if (ActionType.MODIFIED.equals(instance.getActionType())) {
Application existingApp = applications.getRegisteredApplications(instance.getAppName());
if (existingApp == null) {
applications.addApplication(app);
}
// 修改现有应用程序的实例{}
logger.debug("Modified instance {} to the existing apps ", instance.getId());
applications.getRegisteredApplications(instance.getAppName()).addInstance(instance);
} else if (ActionType.DELETED.equals(instance.getActionType())) {
Application existingApp = applications.getRegisteredApplications(instance.getAppName());
if (existingApp != null) {
// 删除现有应用程序的实例{}
logger.debug("Deleted instance {} to the existing apps ", instance.getId());
existingApp.removeInstance(instance);
/*
* We find all instance list from application(The status of instance status is not only the status is UP but also other status)
* if instance list is empty, we remove the application.
* 我们从应用程序中找到所有的实例列表(实例状态的状态不仅是状态是 UP，
* 还有其他状态)如果实例列表为空，我们删除应用程序。
*/
if (existingApp.getInstancesAsIsFromEureka().isEmpty()) {
applications.removeApplication(existingApp);
}
}
}
}
}
logger.debug("The total number of instances fetched by the delta processor : {}", deltaCount);
getApplications().setVersion(delta.getVersion());
// 对提供的实例进行洗牌，以便它们不总是以相同的顺序返回。
getApplications().shuffleInstances(clientConfig.shouldFilterOnlyUpInstances());
for (Applications applications : remoteRegionVsApps.values()) {
applications.setVersion(delta.getVersion());
// 对提供的实例进行洗牌，以便它们不总是以相同的顺序返回。
applications.shuffleInstances(clientConfig.shouldFilterOnlyUpInstances());
}
}主要逻辑：
@Override
public List<ServiceInstance> getInstances(String serviceId) {
// 委托eurekaClient处理
List<InstanceInfo> infos = this.eurekaClient.getInstancesByVipAddress(serviceId,
false);
List<ServiceInstance> instances = new ArrayList<>();
for (InstanceInfo info : infos) {
instances.add(new EurekaServiceInstance(info));
}
return instances;
}跟Nacos的入口是类似的，需要实现spring-cloud-commons的DiscoveryClient接口。这里EurekaDiscoveryClient会委托Eureka项目里面的EurekaClient处理，见下面2分析。然后将Instances列表转换为spring-cloud-commons里面的ServiceInstance类型列表。
@Override
public List<InstanceInfo> getInstancesByVipAddress(String vipAddress, boolean secure) {
return getInstancesByVipAddress(vipAddress, secure, instanceRegionChecker.getLocalRegion());
}
@Override
public List<InstanceInfo> getInstancesByVipAddress(String vipAddress, boolean secure,
@Nullable String region) {
if (vipAddress == null) {
throw new IllegalArgumentException(
"Supplied VIP Address cannot be null");
}
Applications applications;
// 如果eureka:region:没有指定，则使用默认值且非空，即默认使用默认localRegion
if (instanceRegionChecker.isLocalRegion(region)) {
// 本地获取
applications = this.localRegionApps.get();
} else {
applications = remoteRegionVsApps.get(region);
if (null == applications) {
logger.debug("No applications are defined for region {}, so returning an empty instance list for vip "
+ "address {}.", region, vipAddress);
return Collections.emptyList();
}
}
// secure默认false
if (!secure) {
return applications.getInstancesByVirtualHostName(vipAddress);
} else {
return applications.getInstancesBySecureVirtualHostName(vipAddress);
}
}主要逻辑：
