Eureka源码学习（三）—|Eureka源码学习（三）— Eureka Server源码解析 Eureka源码学习（三）—EurekaS

InstanceRegistry InstanceRegistry是Eureka Server中注册表管理的核心接口。在根据类图可以发现它实现了LookUpService和LeaseManager接口。
LeaseManager主要用于维护实例的注册、续租、下线和清理，而LookupService提供对服务实例进行检索的功能。
实例的居住证Lease 初始化
初始化赋值注册时间和上次更新时间

public Lease(T r, int durationInSecs) { holder = r; registrationTimestamp = System.currentTimeMillis(); lastUpdateTimestamp = registrationTimestamp; duration = (durationInSecs * 1000); }

服务下线

// 下线实例 public void cancel() { if (evictionTimestamp <= 0) { evictionTimestamp = System.currentTimeMillis(); } }// 判断是否已经清理 public boolean isExpired() { return isExpired(0l); }// 判断是否已经清理 public boolean isExpired(long additionalLeaseMs) { // 在cancel中可以发现evictionTimestamp被设置为大于0的清理时时间戳 // additionalLeaseMs // ① 清理定时任务中入参为0 // return (evictionTimestamp > 0 || System.currentTimeMillis() > (lastUpdateTimestamp + duration + additionalLeaseMs)); }

Eureka Server服务器用ConcurrentHashMap维护实例注册信息。

// ConcurrentHashMap<应用名, Map<实例id, Lease<实例信息>>> private final ConcurrentHashMap>> registry = new ConcurrentHashMap>>();

租约更新

@PUT public Response renewLease( @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication, @QueryParam("overriddenstatus") String overriddenStatus, @QueryParam("status") String status, @QueryParam("lastDirtyTimestamp") String lastDirtyTimestamp) { // 是否是同步节点来的，避免 boolean isFromReplicaNode = "true".equals(isReplication); // 进行续租操作 boolean isSuccess = registry.renew(app.getName(), id, isFromReplicaNode); // Not found in the registry, immediately ask for a register if (!isSuccess) { // 续租失败，该实例未注册，返回404 logger.warn("Not Found (Renew): {} - {}", app.getName(), id); return Response.status(Status.NOT_FOUND).build(); } // Check if we need to sync based on dirty time stamp, the client // instance might have changed some value Response response; // 防止并发冲突 if (lastDirtyTimestamp != null && serverConfig.shouldSyncWhenTimestampDiffers()) { response = this.validateDirtyTimestamp(Long.valueOf(lastDirtyTimestamp), isFromReplicaNode); // Store the overridden status since the validation found out the node that replicates wins 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 { // 成功续租 response = Response.ok().build(); } logger.debug("Found (Renew): {} - {}; reply status={}", app.getName(), id, response.getStatus()); return response; }

AbstractInstanceRegistry#renew()
对于续租的方法，不想注册一样需要整个实例信息，只需要实例名称和对应的实例id即可完成续租。

public boolean renew(String appName, String id, boolean isReplication) { RENEW.increment(isReplication); Map> gMap = registry.get(appName); Lease leaseToRenew = null; if (gMap != null) { leaseToRenew = gMap.get(id); } if (leaseToRenew == null) { RENEW_NOT_FOUND.increment(isReplication); logger.warn("DS: Registry: lease doesn't exist, registering resource: {} - {}", appName, id); return false; } else { // 获取实例信息 InstanceInfo instanceInfo = leaseToRenew.getHolder(); if (instanceInfo != null) { // touchASGCache(instanceInfo.getASGName()); InstanceStatus overriddenInstanceStatus = this.getOverriddenInstanceStatus( instanceInfo, leaseToRenew, isReplication); //如果得到的服务实例最后状态是UNKNOW，取消续约直接return 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; } // 服务状态不一致。 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()); instanceInfo.setStatusWithoutDirty(overriddenInstanceStatus); } } // 统计每分钟续租的次数，用于自我保护机制 renewsLastMin.increment(); // 更新上次更新时间 leaseToRenew.renew(); return true; } }

Lease#renew()

// 更新上次更新时间 public void renew() { lastUpdateTimestamp = System.currentTimeMillis() + duration; }

过期租约清理 【Eureka源码学习（三）—|Eureka源码学习（三）— Eureka Server源码解析】在AbstractInstanceRegistry中存在EvictionTask用于定时执行exict(0)来服务剔除，默认为60秒一次。但是如果Eureka Server处于自我保护状态，则无法进行清理操作。在进入自我保护状态后，在Eureka Client处，如果向Eureka Server注册失败，将快速超时并尝试与其他的Eureka Server进行通信。“自我保护机制”的设计大大提高了Eureka的可用性。

public void evict(long additionalLeaseMs) { logger.debug("Running the evict task"); // 判断是否打开了自我保护机制 // isLeaseExpirationEnabled == true 代表未开启自我保护机制 if (!isLeaseExpirationEnabled()) { logger.debug("DS: lease expiration is currently disabled."); return; }// 遍历resgistry保存的注册信息，用expiredLeases收集所有过期的实例信息 List> expiredLeases = new ArrayList<>(); for (Entry>> groupEntry : registry.entrySet()) { // 对每个应用的实例列表判断是否需要清理 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(); // 获取注册的实例数 int registrySizeThreshold = (int) (registrySize * serverConfig.getRenewalPercentThreshold()); // 获得阈值 0.85（default）*size // 计算清理数量限制 evictionLimit = // 注册实例数 - 注册实例数 * 0.85（default） = 0.15 * 注册实例数 int evictionLimit = registrySize - registrySizeThreshold; // 在limit和需要清理的数量中取较小值 int toEvict = Math.min(expiredLeases.size(), evictionLimit); // 存在需要清理的实例，这里使用随机算法进行删除 if (toEvict > 0) { logger.info("Evicting {} items (expired={}, evictionLimit={})", toEvict, expiredLeases.size(), evictionLimit); // 用随机算法cancel实例 // 根据前面的保护机制，最大下线Math.min(expiredLeases.size(), evictionLimit)个实例 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); // !! 注意，服务是逐个清理的 internalCancel(appName, id, false); } } }