序
本文主要研究下eureka的renewal
client
eureka client在实例化的时候注册了一个定时任务，每隔renewalIntervalInSecs，向eureka server发送一次renewal。具体详见聊聊eureka client的HeartbeatThread
server
PeerAwareInstanceRegistryImpl.init
eureka-core-1.8.8-sources.jar!/com/netflix/eureka/registry/PeerAwareInstanceRegistryImpl.java
@Override
public void init(PeerEurekaNodes peerEurekaNodes) throws Exception {
this.numberOfReplicationsLastMin.start();
this.peerEurekaNodes = peerEurekaNodes;
initializedResponseCache();
scheduleRenewalThresholdUpdateTask();
initRemoteRegionRegistry();
try {
Monitors.registerObject(this);
} catch (Throwable e) {
logger.warn("Cannot register the JMX monitor for the InstanceRegistry :", e);
}
}这里设定了更新RenewalThreshold的定时任务
scheduleRenewalThresholdUpdateTask
/**
* Schedule the task that updates renewal threshold periodically.
* The renewal threshold would be used to determine if the renewals drop
* dramatically because of network partition and to protect expiring too
* many instances at a time.
*
*/
private void scheduleRenewalThresholdUpdateTask() {
timer.schedule(new TimerTask() {
@Override
public void run() {
updateRenewalThreshold();
}
}, serverConfig.getRenewalThresholdUpdateIntervalMs(),
serverConfig.getRenewalThresholdUpdateIntervalMs());
}间隔RenewalThresholdUpdateIntervalMs调度一次
updateRenewalThreshold(numberOfRenewsPerMinThreshold更新)
/**
* Updates the renewal threshold based on the current number of
* renewals. The threshold is a percentage as specified in
* {@link EurekaServerConfig#getRenewalPercentThreshold()} of renewals
* received per minute {@link #getNumOfRenewsInLastMin()}.
*/
private void updateRenewalThreshold() {
try {
Applications apps = eurekaClient.getApplications();
int count = 0;
for (Application app : apps.getRegisteredApplications()) {
for (InstanceInfo instance : app.getInstances()) {
if (this.isRegisterable(instance)) {
++count;
}
}
}
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);
}
}numberOfRenewsPerMinThreshold使用
eureka-core-1.8.8-sources.jar!/com/netflix/eureka/registry/PeerAwareInstanceRegistryImpl.java
@Override
public boolean isLeaseExpirationEnabled() {
if (!isSelfPreservationModeEnabled()) {
// The self preservation mode is disabled, hence allowing the instances to expire.
return true;
}
return numberOfRenewsPerMinThreshold > 0 && getNumOfRenewsInLastMin() > numberOfRenewsPerMinThreshold;
}PeerAwareInstanceRegistryImpl.openForTraffic
eureka-core-1.8.8-sources.jar!/com/netflix/eureka/registry/PeerAwareInstanceRegistryImpl.java
public void openForTraffic(ApplicationInfoManager applicationInfoManager, int count) {
// Renewals happen every 30 seconds and for a minute it should be a factor of 2.
this.expectedNumberOfRenewsPerMin = count * 2;
this.numberOfRenewsPerMinThreshold =
(int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold());
logger.info("Got {} instances from neighboring DS node", count);
logger.info("Renew threshold is: {}", numberOfRenewsPerMinThreshold);
this.startupTime = System.currentTimeMillis();
if (count > 0) {
this.peerInstancesTransferEmptyOnStartup = false;
}
DataCenterInfo.Name selfName = applicationInfoManager.getInfo().getDataCenterInfo().getName();
boolean isAws = Name.Amazon == selfName;
if (isAws && serverConfig.shouldPrimeAwsReplicaConnections()) {
logger.info("Priming AWS connections for all replicas..");
primeAwsReplicas(applicationInfoManager);
}
logger.info("Changing status to UP");
applicationInfoManager.setInstanceStatus(InstanceStatus.UP);
super.postInit();
}这个方法调用了super.postInit()
super.postInit()
eureka-core-1.8.8-sources.jar!/com/netflix/eureka/registry/AbstractInstanceRegistry.java
protected void postInit() {
renewsLastMin.start();
if (evictionTaskRef.get() != null) {
evictionTaskRef.get().cancel();
}
evictionTaskRef.set(new EvictionTask());
evictionTimer.schedule(evictionTaskRef.get(),
serverConfig.getEvictionIntervalTimerInMs(),
serverConfig.getEvictionIntervalTimerInMs());
}这里调度了EvictionTask，时间间隔为EvictionIntervalTimerInMs
EvictionTask
eureka-core-1.8.8-sources.jar!/com/netflix/eureka/registry/AbstractInstanceRegistry.java
class EvictionTask extends TimerTask {
private final AtomicLong lastExecutionNanosRef = new AtomicLong(0l);
@Override
public void run() {
try {
long compensationTimeMs = getCompensationTimeMs();
logger.info("Running the evict task with compensationTime {}ms", compensationTimeMs);
evict(compensationTimeMs);
} catch (Throwable e) {
logger.error("Could not run the evict task", e);
}
}
/**
* compute a compensation time defined as the actual time this task was executed since the prev iteration,
* vs the configured amount of time for execution. This is useful for cases where changes in time (due to
* clock skew or gc for example) causes the actual eviction task to execute later than the desired time
* according to the configured cycle.
*/
long getCompensationTimeMs() {
long currNanos = getCurrentTimeNano();
long lastNanos = lastExecutionNanosRef.getAndSet(currNanos);
if (lastNanos == 0l) {
return 0l;
}
long elapsedMs = TimeUnit.NANOSECONDS.toMillis(currNanos - lastNanos);
long compensationTime = elapsedMs - serverConfig.getEvictionIntervalTimerInMs();
return compensationTime <= 0l ? 0l : compensationTime;
}
long getCurrentTimeNano() { // for testing
return System.nanoTime();
}
}补偿时间=当前时间点-task最近一次执行的时间点-清除间隔，小于0则取0
evict方法
public void evict(long additionalLeaseMs) {
logger.debug("Running the evict task");
if (!isLeaseExpirationEnabled()) {
logger.debug("DS: lease expiration is currently disabled.");
return;
}
// 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) {
expiredLeases.add(lease);
}
}
}
}
// 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;
int toEvict = Math.min(expiredLeases.size(), evictionLimit);
if (toEvict > 0) {
logger.info("Evicting {} items (expired={}, evictionLimit={})", toEvict, expiredLeases.size(), evictionLimit);
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);
}
}
} 若最后更新时间 + lease的存活时间[默认是90s]+补偿时间 < 当前时间，则过期。
小结
对于renewal，一方面是client端定时任务主动去续约，一方面是server端不断更新renewThreshold，然后又有定时任务去清理过期的renewal。
doc
- eureka的惊群效应
- eureka如何剔除实例
- eureka的RateLimiter
- 理解eureka的自我保护机制
- EurekaClient如何更新注册信息
- 聊聊eureka client的HeartbeatThread
- 聊聊eureka的PeerAwareInstanceRegistryImpl