eureka服务注册过程

eureka服务端

    eurekaServer是服务的注册中心，负责eureka client相关信息的注册，主要职责有

• 服务注册
• 心跳服务
• 服务剔除
• 服务下线
• 集群同步

    首先我们看eureka-server包里META-INF下的spring.factories文件里的启动类EurekaServerAutoConfiguration。

找到peerAwareInstanceRegistry方法

	@Bean
	public PeerAwareInstanceRegistry peerAwareInstanceRegistry(
			ServerCodecs serverCodecs) {
		this.eurekaClient.getApplications(); // force initialization
		return new InstanceRegistry(this.eurekaServerConfig, this.eurekaClientConfig,
				serverCodecs, this.eurekaClient,
				this.instanceRegistryProperties.getExpectedNumberOfClientsSendingRenews(),
				this.instanceRegistryProperties.getDefaultOpenForTrafficCount());
	}

    再找到InstanceRegistry的父类PeerAwareInstanceRegistryImpl，再继续往上找父类实现的接口PeerAwareInstanceRegistry，继续往上找父类InstanceRegistry，再继续往上找最终找到LeaseManager接口。然后我们去它的实现类中看具体的实现。

public interface LeaseManager {
   // 注册
    void register(T var1, int var2, boolean var3);
    // 服务下线
    boolean cancel(String var1, String var2, boolean var3);
    // 服务更新
    boolean renew(String var1, String var2, boolean var3);
    // 服务剔除
    void evict();
}

• 服务注册register()

    注册方法中起主要作用的就是前面的这段代码

// 加锁
            this.read.lock();
			// 可以看到他的注册中心就是一个hashmap
            Map> gMap = (Map)this.registry.get(registrant.getAppName());
            EurekaMonitors.REGISTER.increment(isReplication);
            if (gMap == null) {
                ConcurrentHashMap> gNewMap = new ConcurrentHashMap();
				// 尝试将注册信息注册到map中，如果已经存在就返回
                gMap = (Map)this.registry.putIfAbsent(registrant.getAppName(), gNewMap);
                if (gMap == null) {
                    gMap = gNewMap;
                }
            }

            Lease existingLease = (Lease)((Map)gMap).get(registrant.getId());
            if (existingLease != null && existingLease.getHolder() != null) {
                Long existingLastDirtyTimestamp = ((InstanceInfo)existingLease.getHolder()).getLastDirtyTimestamp();
                Long registrationLastDirtyTimestamp = registrant.getLastDirtyTimestamp();
                logger.debug("Existing lease found (existing={}, provided={}", existingLastDirtyTimestamp, registrationLastDirtyTimestamp);
                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 = (InstanceInfo)existingLease.getHolder();
                }
            } else {
			    // 如果没有租约信息，则注册
                Object var6 = this.lock;
                synchronized(this.lock) {
                    if (this.expectedNumberOfClientsSendingRenews > 0) {
                        ++this.expectedNumberOfClientsSendingRenews;
                        this.updateRenewsPerMinThreshold();
                    }
                }

                logger.debug("No previous lease information found; it is new registration");
            }

• 心跳服务renew()

    心跳服务就是一个续约服务。

public boolean renew(String appName, String id, boolean isReplication) {
        EurekaMonitors.RENEW.increment(isReplication);
		// 从注册中心获取租约信息
        Map> gMap = (Map)this.registry.get(appName);
        Lease leaseToRenew = null;
        if (gMap != null) {
            leaseToRenew = (Lease)gMap.get(id);
        }

        if (leaseToRenew == null) {
		    // 如果没有租约信息，那么说明没有注册，直接退出
            EurekaMonitors.RENEW_NOT_FOUND.increment(isReplication);
            logger.warn("DS: Registry: lease doesn't exist, registering resource: {} - {}", appName, id);
            return false;
        } else {
            InstanceInfo instanceInfo = (InstanceInfo)leaseToRenew.getHolder();
            if (instanceInfo != null) {
                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());
                    EurekaMonitors.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", new Object[]{instanceInfo.getStatus().name(), instanceInfo.getOverriddenStatus().name(), instanceInfo.getId()});
                    instanceInfo.setStatusWithoutDirty(overriddenInstanceStatus);
                }
            }

            this.renewsLastMin.increment();
            // 这里是真正续约的操作
            leaseToRenew.renew();
            return true;
        }
    }

    public void renew() {
        lastUpdateTimestamp = System.currentTimeMillis() + duration;

    }

• 服务剔除

    如果服务既没有下线，也没有续约（即心跳），那么就执行服务剔除。

    服务剔除是一个线程在跑

    protected void postInit() {
        renewsLastMin.start();
        if (evictionTaskRef.get() != null) {
            evictionTaskRef.get().cancel();
        }
        evictionTaskRef.set(new EvictionTask());
        evictionTimer.schedule(evictionTaskRef.get(),
                serverConfig.getEvictionIntervalTimerInMs(),
                serverConfig.getEvictionIntervalTimerInMs());
    }

可以看到EvictionTask 方法中执行了evict方法

        @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);
            }
        }

    public void evict(long additionalLeaseMs) {
        logger.debug("Running the evict task");
		// 如果开启了保护机制，那么不会执行服务剔除
        if (!isLeaseExpirationEnabled()) {
            logger.debug("DS: lease expiration is currently disabled.");
            return;
        }

        // 遍历注册中心所有的租约信息，获取需要剔除的服务
        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);
                    }
                }
            }
        }

        
        int registrySize = (int) getLocalRegistrySize();
        int registrySizeThreshold = (int) (registrySize * serverConfig.getRenewalPercentThreshold());
        // 允许剔除的服务数量
		int evictionLimit = registrySize - registrySizeThreshold;
		// 获取最小值，即最后最多删除的数量
        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());
			// 进行遍历
            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);
				// 执行服务下线
                internalCancel(appName, id, false);
            }
        }
    }

 

• 服务下线

    protected boolean internalCancel(String appName, String id, boolean isReplication) {
        try {
            read.lock();
            CANCEL.increment(isReplication);
            Map> gMap = registry.get(appName);
            Lease leaseToCancel = null;
            if (gMap != null) {
               // 将服务删除
                leaseToCancel = gMap.remove(id);
            }
            synchronized (recentCanceledQueue) {
                recentCanceledQueue.add(new Pair(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();
        }
    }

• 集群同步

1. EurekaServer在启动过程中从他的peer节点中拉取注册表信息，并将这些服务实例注册到本地注册表中；
2. 是eureka server每次对本地注册表进行操作时，同时会讲操作同步到他的peer节点中，达到数据一致；

public interface PeerAwareInstanceRegistry extends InstanceRegistry {

    void init(PeerEurekaNodes peerEurekaNodes) throws Exception;
    // 服务同步
    int syncUp();

  
     boolean shouldAllowAccess(boolean remoteRegionRequired);

     void register(InstanceInfo info, boolean isReplication);

     void statusUpdate(final String asgName, final ASGResource.ASGStatus newStatus, final boolean isReplication);
}

• 服务拉取

    public int syncUp() {
        // Copy entire entry from neighboring DS node
        int count = 0;

        for (int i = 0; ((i < serverConfig.getRegistrySyncRetries()) && (count == 0)); i++) {
            if (i > 0) {
                try {
				    // 每隔多久同步一次
                    Thread.sleep(serverConfig.getRegistrySyncRetryWaitMs());
                } catch (InterruptedException e) {
                    logger.warn("Interrupted during registry transfer..");
                    break;
                }
            }
			// 从其他节点获取注册信息，并进行本地注册
            Applications apps = eurekaClient.getApplications();
            for (Application app : apps.getRegisteredApplications()) {
                for (InstanceInfo instance : app.getInstances()) {
                    try {
                        if (isRegisterable(instance)) {
                            register(instance, instance.getLeaseInfo().getDurationInSecs(), true);
                            count++;
                        }
                    } catch (Throwable t) {
                        logger.error("During DS init copy", t);
                    }
                }
            }
        }
        return count;
    }

• 服务同步

    @Override
    public boolean cancel(final String appName, final String id,
                          final boolean isReplication) {
        // 调用父类的下线方法
        if (super.cancel(appName, id, isReplication)) {
            // 将信息同步到其他节点
            replicateToPeers(Action.Cancel, appName, id, null, null, isReplication);
            synchronized (lock) {
                if (this.expectedNumberOfClientsSendingRenews > 0) {
                    // Since the client wants to cancel it, reduce the number of clients to send renews
                    this.expectedNumberOfClientsSendingRenews = this.expectedNumberOfClientsSendingRenews - 1;
                    updateRenewsPerMinThreshold();
                }
            }
            return true;
        }
        return false;
    }

 

eureka客户端

    客户端就是将服务信息提交到服务端。它主要的工作有

初始化阶段

1. 读取与 Eureka Server交互的配置信息,封装成 EurekaClientConfig
2. 读取自身服务实例配置信息,封装成EurekalnstanceConfig
3. 从Eureka server拉取注册表信息并缓存到本地
4. 服务注册
5. 初始化发送心跳、缓存刷新(拉取注册表信息更新本地缓存)和按需注册(监控服务实例信息变化,决定是否重新发起注册,更新注册表中的服务实例元数据)定时任务

应用启动阶段

1. 定时发送心跳到Eureka Server中维持在注册表的租约
2. 定时从 Eureka Server中拉取注册表信息,更新本地注册表缓存
3. 监控应用自身信息变化,若发生变化,需要重新发起服务注册
4. 从 Eureka Server注销自身服务实例