下面来说下eureka的自我保护机制。当每分钟心跳次数( renewsLastMin ) 小于 numberOfRenewsPerMinThreshold 时，并且开启自动保护模式开关( eureka.enableSelfPreservation = true ) 时，触发自动保护机制，不再自动过期租约
public void evict(long additionalLeaseMs) {
logger.debug("Running the evict task");
if (!isLeaseExpirationEnabled()) {
logger.debug("DS: lease expiration is currently disabled.");
return;
}
// 获得 所有过期的租约
// We collect first all expired items, to evict them in random order. For large eviction sets,
// if we do not that, we might wipe out whole apps before self preservation kicks in. By randomizing it,
// the impact should be evenly distributed across all applications.
List> expiredLeases = new ArrayList<>();
for (Entry>> groupEntry : registry.entrySet()) {
Map> leaseMap = groupEntry.getValue();
if (leaseMap != null) {
for (Entry> leaseEntry : leaseMap.entrySet()) {
Lease lease = leaseEntry.getValue();
if (lease.isExpired(additionalLeaseMs) && lease.getHolder() != null) { // 过期
expiredLeases.add(lease);
}
}
}
}
// 计算 最大允许清理租约数量
// To compensate for GC pauses or drifting local time, we need to use current registry size as a base for
// triggering self-preservation. Without that we would wipe out full registry.
int registrySize = (int) getLocalRegistrySize();
int registrySizeThreshold = (int) (registrySize * serverConfig.getRenewalPercentThreshold());
int evictionLimit = registrySize - registrySizeThreshold;
// 计算 清理租约数量
int toEvict = Math.min(expiredLeases.size(), evictionLimit);
if (toEvict > 0) {
logger.info("Evicting {} items (expired={}, evictionLimit={})", toEvict, expiredLeases.size(), evictionLimit);
// 逐个过期
Random random = new Random(System.currentTimeMillis());
for (int i = 0; i < toEvict; i++) {
// Pick a random item (Knuth shuffle algorithm)
int next = i + random.nextInt(expiredLeases.size() - i);
Collections.swap(expiredLeases, i, next);
Lease lease = expiredLeases.get(i);
String appName = lease.getHolder().getAppName();
String id = lease.getHolder().getId();
EXPIRED.increment();
logger.warn("DS: Registry: expired lease for {}/{}", appName, id);
internalCancel(appName, id, false);
}
}
}
EurekaServer 在启动时，从 EurekaServer集群获取注册信息，并首次初始化 numberOfRenewsPerMinThreshold 、 expectedNumberOfRenewsPerMin。Eureka-Server 定时重新计算 numberOfRenewsPerMinThreshold 、expectedNumberOfRenewsPerMin 。
private void scheduleRenewalThresholdUpdateTask() {
timer.schedule(new TimerTask() {
@Override
public void run() {
updateRenewalThreshold();
}
}, serverConfig.getRenewalThresholdUpdateIntervalMs(),
serverConfig.getRenewalThresholdUpdateIntervalMs());
}
private void updateRenewalThreshold() {
try {
// 计算 应用实例数
Applications apps = eurekaClient.getApplications();
int count = 0;
for (Application app : apps.getRegisteredApplications()) {
for (InstanceInfo instance : app.getInstances()) {
if (this.isRegisterable(instance)) {
++count;
}
}
}
// 计算 expectedNumberOfRenewsPerMin 、 numberOfRenewsPerMinThreshold 参数
synchronized (lock) {
// Update threshold only if the threshold is greater than the
// current expected threshold of if the self preservation is disabled.
if ((count * 2) > (serverConfig.getRenewalPercentThreshold() * numberOfRenewsPerMinThreshold)
|| (!this.isSelfPreservationModeEnabled())) {
this.expectedNumberOfRenewsPerMin = count * 2;
this.numberOfRenewsPerMinThreshold = (int) ((count * 2) * serverConfig.getRenewalPercentThreshold());
}
}
logger.info("Current renewal threshold is : {}", numberOfRenewsPerMinThreshold);
} catch (Throwable e) {
logger.error("Cannot update renewal threshold", e);
}
}
配置
eureka.renewalThresholdUpdateIntervalMs参数，定时重新计算。默认，15 分钟。代码块
!this.isSelfPreservationModeEnabled()：当未开启自我保护机制时，每次都进行重新计算。事实上，这两个参数不仅仅自我保护机制会使用到，配合 Netflix Servo实现监控信息采集numberOfRenewsPerMinThreshold、expectedNumberOfRenewsPerMin。-
代码块
(count * 2) > (serverConfig.getRenewalPercentThreshold() * numberOfRenewsPerMinThreshold)：当开启自我保护机制时，应用实例每分钟最大心跳数(count * 2) 小于期望最小每分钟续租次数(serverConfig.getRenewalPercentThreshold() * numberOfRenewsPerMinThreshold)，不重新计算。如果重新计算，自动保护机制会每次定时执行后失效。
应用实例注册时，增加 numberOfRenewsPerMinThreshold 、expectedNumberOfRenewsPerMin。public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) { try { // 获取读锁 read.lock(); MapexistingLease = gMap.get(registrant.getId()); // Retain the last dirty timestamp without overwriting it, if there is already a lease if (existingLease != null && (existingLease.getHolder() != null)) { // 已存在时，使用数据不一致的时间大的应用注册信息为有效的 Long existingLastDirtyTimestamp = existingLease.getHolder().getLastDirtyTimestamp(); // Server 注册的 InstanceInfo Long registrationLastDirtyTimestamp = registrant.getLastDirtyTimestamp(); // Client 请求的 InstanceInfo logger.debug("Existing lease found (existing={}, provided={}", existingLastDirtyTimestamp, registrationLastDirtyTimestamp); // this is a > instead of a >= because if the timestamps are equal, we still take the remote transmitted // InstanceInfo instead of the server local copy. if (existingLastDirtyTimestamp > registrationLastDirtyTimestamp) { logger.warn("There is an existing lease and the existing lease's dirty timestamp {} is greater" + " than the one that is being registered {}", existingLastDirtyTimestamp, registrationLastDirtyTimestamp); logger.warn("Using the existing instanceInfo instead of the new instanceInfo as the registrant"); registrant = existingLease.getHolder(); } } else { // The lease does not exist and hence it is a new registration // 【自我保护机制】增加 `numberOfRenewsPerMinThreshold` 、`expectedNumberOfRenewsPerMin` synchronized (lock) { if (this.expectedNumberOfRenewsPerMin > 0) { // Since the client wants to cancel it, reduce the threshold // (1 // for 30 seconds, 2 for a minute) this.expectedNumberOfRenewsPerMin = this.expectedNumberOfRenewsPerMin + 2; this.numberOfRenewsPerMinThreshold = (int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold()); } } logger.debug("No previous lease information found; it is new registration"); } // 创建 租约 Lease lease = new Lease (registrant, leaseDuration); if (existingLease != null) { // 若租约已存在，设置 租约的开始服务的时间戳 lease.setServiceUpTimestamp(existingLease.getServiceUpTimestamp()); } // 添加到 租约映射 gMap.put(registrant.getId(), lease); // 添加到 最近注册的调试队列 synchronized (recentRegisteredQueue) { recentRegisteredQueue.add(new Pair }
应用实例下线时，减少 numberOfRenewsPerMinThreshold 、expectedNumberOfRenewsPerMin。protected boolean internalCancel(String appName, String id, boolean isReplication) { try { // 获得读锁 read.lock(); // 增加 取消注册次数 到 监控 CANCEL.increment(isReplication); // 移除 租约映射 MapleaseToCancel = null; if (gMap != null) { leaseToCancel = gMap.remove(id); } // 添加到 最近取消注册的调试队列 synchronized (recentCanceledQueue) { recentCanceledQueue.add(new Pair
eureka的自我保护机制就介绍到这里了。