Eureka客户端续约及服务端过期租约清理源码解析

在之前的文章：EurekaClient自动装配及启动流程解析中，我们提到了在构造DiscoveryClient时除了包含注册流程之外，还调度了一个心跳线程：

scheduler.schedule(
                    new TimedSupervisorTask(
                            "heartbeat",
                            scheduler,
                            heartbeatExecutor,
                            renewalIntervalInSecs,
                            TimeUnit.SECONDS,
                            expBackOffBound,
                            new HeartbeatThread()
                    ),
                    renewalIntervalInSecs, TimeUnit.SECONDS);

其中HeartbeatThread线程如下：

    private class HeartbeatThread implements Runnable {

        public void run() {
        //续约
            if (renew()) {
			  //续约成功时间戳更新
                lastSuccessfulHeartbeatTimestamp = System.currentTimeMillis();
            }
        }
    }

 boolean renew() {
        EurekaHttpResponse<InstanceInfo> httpResponse;
        try {
		  //发送续约请求
            httpResponse = eurekaTransport.registrationClient.sendHeartBeat(instanceInfo.getAppName(), instanceInfo.getId(), instanceInfo, null);
            logger.debug(PREFIX + "{} - Heartbeat status: {}", appPathIdentifier, httpResponse.getStatusCode());
            if (httpResponse.getStatusCode() == 404) {
                REREGISTER_COUNTER.increment();
                logger.info(PREFIX + "{} - Re-registering apps/{}", appPathIdentifier, instanceInfo.getAppName());
                long timestamp = instanceInfo.setIsDirtyWithTime();
			  //重新注册
                boolean success = register();
                if (success) {
                    instanceInfo.unsetIsDirty(timestamp);
                }
                return success;
            }
            return httpResponse.getStatusCode() == 200;
        } catch (Throwable e) {
            logger.error(PREFIX + "{} - was unable to send heartbeat!", appPathIdentifier, e);
            return false;
        }
    }

这里直接发出了续约请求，如果续约请求失败则会尝试再次去注册

服务端接受续约请求

服务端接受续约请求的Controller在InstanceResource类中

@PUT
    public Response renewLease(
            @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication,
            @QueryParam("overriddenstatus") String overriddenStatus,
            @QueryParam("status") String status,
            @QueryParam("lastDirtyTimestamp") String lastDirtyTimestamp) {
        boolean isFromReplicaNode = "true".equals(isReplication);
	  //续约
        boolean isSuccess = registry.renew(app.getName(), id, isFromReplicaNode);

        // 续约失败
        if (!isSuccess) {
            logger.warn("Not Found (Renew): {} - {}", app.getName(), id);
            return Response.status(Status.NOT_FOUND).build();
        }
        // 校验客户端与服务端的时间差异，如果存在问题则需要重新发起注册
        Response response = null;
        if (lastDirtyTimestamp != null && serverConfig.shouldSyncWhenTimestampDiffers()) {
            response = this.validateDirtyTimestamp(Long.valueOf(lastDirtyTimestamp), isFromReplicaNode);
            if (response.getStatus() == Response.Status.NOT_FOUND.getStatusCode()
                    && (overriddenStatus != null)
                    && !(InstanceStatus.UNKNOWN.name().equals(overriddenStatus))
                    && isFromReplicaNode) {
                registry.storeOverriddenStatusIfRequired(app.getAppName(), id, InstanceStatus.valueOf(overriddenStatus));
            }
        } else {
            response = Response.ok().build();
        }
        logger.debug("Found (Renew): {} - {}; reply status={}", app.getName(), id, response.getStatus());
        return response;
    }

可以看到续约之后还有一个检查时间差的问题，这个不详细展开，继续往下看续约的相关信息

    public boolean renew(final String appName, final String id, final boolean isReplication) {
        if (super.renew(appName, id, isReplication)) {
		  //集群同步
            replicateToPeers(Action.Heartbeat, appName, id, null, null, isReplication);
            return true;
        }
        return false;
    }

这里集群同步的相关内容在之前的文章已经说过了，不再展开，续约的核心处理在下面

 public boolean renew(String appName, String id, boolean isReplication) {
        RENEW.increment(isReplication);
   //获取已存在的租约
        Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
        Lease<InstanceInfo> leaseToRenew = null;
        if (gMap != null) {
            leaseToRenew = gMap.get(id);
        }
   //租约不存在
        if (leaseToRenew == null) {
            RENEW_NOT_FOUND.increment(isReplication);
            logger.warn("DS: Registry: lease doesn't exist, registering resource: {} - {}", appName, id);
            return false;
        } else {
		  //获取客户端
            InstanceInfo instanceInfo = leaseToRenew.getHolder();
		  //设置客户端的状态
            if (instanceInfo != null) {
                // touchASGCache(instanceInfo.getASGName());
                InstanceStatus overriddenInstanceStatus = this.getOverriddenInstanceStatus(
                        instanceInfo, leaseToRenew, isReplication);
                if (overriddenInstanceStatus == InstanceStatus.UNKNOWN) {
                    logger.info("Instance status UNKNOWN possibly due to deleted override for instance {}"
                            + "; re-register required", instanceInfo.getId());
                    RENEW_NOT_FOUND.increment(isReplication);
                    return false;
                }
                if (!instanceInfo.getStatus().equals(overriddenInstanceStatus)) {
                    logger.info(
                            "The instance status {} is different from overridden instance status {} for instance {}. "
                                    + "Hence setting the status to overridden status", instanceInfo.getStatus().name(),
                                    instanceInfo.getOverriddenStatus().name(),
                                    instanceInfo.getId());
				  //覆盖当前状态
                    instanceInfo.setStatusWithoutDirty(overriddenInstanceStatus);

                }
            }
            renewsLastMin.increment();
		  //设置租约最后更新时间
            leaseToRenew.renew();
            return true;
        }
    }

对于看过之前文章的同学来说整体流程比较简单

服务端过期租约清理

在文章Eureka应用注册与集群数据同步源码解析一文中大家应该对下面这行代码比较熟悉

int registryCount = registry.syncUp();

上面这行代码发起了集群数据同步，而紧接着这行代码的就是服务端的过期租约清理逻辑

registry.openForTraffic(applicationInfoManager, registryCount);

openForTraffic方法的最后调用了一个方法postInit，而在postInit方法中启动了一个线程EvictionTask，这个线程就负责清理已经过期的租约

evictionTimer.schedule(evictionTaskRef.get(),       
serverConfig.getEvictionIntervalTimerInMs(), 
serverConfig.getEvictionIntervalTimerInMs());

看一下这个线程

class EvictionTask extends TimerTask {

   @Override
   public void run() {
       try {
           //补偿时间毫秒数
           long compensationTimeMs = getCompensationTimeMs();
           logger.info("Running the evict task with compensationTime {}ms", compensationTimeMs);
           // 清理逻辑
           evict(compensationTimeMs);
       } catch (Throwable e) {
           logger.error("Could not run the evict task", e);
       }
   }

}

其中补偿时间的获取是这样的：

long getCompensationTimeMs() {
            long currNanos = getCurrentTimeNano();
            long lastNanos = lastExecutionNanosRef.getAndSet(currNanos);
            if (lastNanos == 0l) {
                return 0l;
            }

            long elapsedMs = TimeUnit.NANOSECONDS.toMillis(currNanos - lastNanos);
            //当前时间 - 最后任务执行时间 - 任务执行频率
            long compensationTime = elapsedMs - serverConfig.getEvictionIntervalTimerInMs();
            return compensationTime <= 0l ? 0l : compensationTime;
        }

接着看清理的核心逻辑

public void evict(long additionalLeaseMs) {
        logger.debug("Running the evict task");

        if (!isLeaseExpirationEnabled()) {
            logger.debug("DS: lease expiration is currently disabled.");
            return;
        }

        // 1. 获得所有的过期租约
        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);
                    }
                }
            }
        }

        // 2. 计算允许清理的数量
        int registrySize = (int) getLocalRegistrySize();
        int registrySizeThreshold = (int) (registrySize * serverConfig.getRenewalPercentThreshold());
        int evictionLimit = registrySize - registrySizeThreshold;
        int toEvict = Math.min(expiredLeases.size(), evictionLimit);

        // 3. 过期
        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);
            }
        }
    }

整个过期的执行过程主要分为以下3个步骤：

1. 获得所有的过期租约
   
   过期租约的计算方法为isExpired

public boolean isExpired(long additionalLeaseMs) {   
    return (evictionTimestamp > 0 || System.currentTimeMillis() >
(lastUpdateTimestamp + duration + additionalLeaseMs));
}

服务下线时间>0||当前时间>(最后更新时间+租约持续时间+补偿时间)

1. 计算允许清理的数量
   
   getRenewalPercentThreshold()默认值为0.85，也是就说默认情况下每次清理最大允许过期数量和15%的所有注册数量两者之间的最小值
2. 过期
   
   过期的清理是随机进行的，这样设计也是为了避免单个应用全部过期的。
   
   过期的处理则和注册的处理正好是相反的：

 protected boolean internalCancel(String appName, String id, boolean isReplication) {
        try {
            read.lock();
            CANCEL.increment(isReplication);
            Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
            Lease<InstanceInfo> leaseToCancel = null;
            if (gMap != null) {
                leaseToCancel = gMap.remove(id);
            }
            synchronized (recentCanceledQueue) {
                recentCanceledQueue.add(new Pair<Long, String>(System.currentTimeMillis(), appName + "(" + id + ")"));
            }
            InstanceStatus instanceStatus = overriddenInstanceStatusMap.remove(id);
            if (instanceStatus != null) {
                logger.debug("Removed instance id {} from the overridden map which has value {}", id, instanceStatus.name());
            }
            if (leaseToCancel == null) {
                CANCEL_NOT_FOUND.increment(isReplication);
                logger.warn("DS: Registry: cancel failed because Lease is not registered for: {}/{}", appName, id);
                return false;
            } else {
                leaseToCancel.cancel();
                InstanceInfo instanceInfo = leaseToCancel.getHolder();
                String vip = null;
                String svip = null;
                if (instanceInfo != null) {
                    instanceInfo.setActionType(ActionType.DELETED);
                    recentlyChangedQueue.add(new RecentlyChangedItem(leaseToCancel));
                    instanceInfo.setLastUpdatedTimestamp();
                    vip = instanceInfo.getVIPAddress();
                    svip = instanceInfo.getSecureVipAddress();
                }
                invalidateCache(appName, vip, svip);
                logger.info("Cancelled instance {}/{} (replication={})", appName, id, isReplication);
                return true;
            }
        } finally {
            read.unlock();
        }
    }

原文地址