聊聊eureka的renewal

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 <em>renewal threshold</em> 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 <em>renewal threshold</em> 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<Lease<InstanceInfo>> expiredLeases = new ArrayList<>();
        for (Entry<String, Map<String, Lease<InstanceInfo>>> groupEntry : registry.entrySet()) {
            Map<String, Lease<InstanceInfo>> leaseMap = groupEntry.getValue();
            if (leaseMap != null) {
                for (Entry<String, Lease<InstanceInfo>> leaseEntry : leaseMap.entrySet()) {
                    Lease<InstanceInfo> 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<InstanceInfo> 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