InstanceRegistry

InstanceRegistry是Eureka Server中注冊表管理的核心接口。在根據(jù)類圖可以發(fā)現(xiàn)它實現(xiàn)了LookUpService和LeaseManager接口。

LeaseManager主要用于維護實例的注冊、續(xù)租、下線和清理，而LookupService提供對服務實例進行檢索的功能。

實例的居住證Lease

初始化

初始化賦值注冊時間和上次更新時間

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

服務下線

// 下線實例
public void cancel() {
  if (evictionTimestamp <= 0) {
    evictionTimestamp = System.currentTimeMillis();
  }
}

// 判斷是否已經(jīng)清理
public boolean isExpired() {
    return isExpired(0l);
}

// 判斷是否已經(jīng)清理
public boolean isExpired(long additionalLeaseMs) {
        // 在cancel中可以發(fā)現(xiàn)evictionTimestamp被設置為大于0的清理時時間戳
            // additionalLeaseMs
            // ① 清理定時任務中入?yún)?
            // 
        return (evictionTimestamp > 0 || System.currentTimeMillis() > (lastUpdateTimestamp + duration + additionalLeaseMs));
}

Eureka Server服務器用ConcurrentHashMap維護實例注冊信息。

// ConcurrentHashMap<應用名, Map<實例id, Lease<實例信息>>>
private final ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>> registry
        = new ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>>();

租約更新

@PUT
public Response renewLease(
        @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication,
        @QueryParam("overriddenstatus") String overriddenStatus,
        @QueryParam("status") String status,
        @QueryParam("lastDirtyTimestamp") String lastDirtyTimestamp) {
    // 是否是同步節(jié)點來的，避免
    boolean isFromReplicaNode = "true".equals(isReplication);
    // 進行續(xù)租操作
    boolean isSuccess = registry.renew(app.getName(), id, isFromReplicaNode);

    // Not found in the registry, immediately ask for a register
    if (!isSuccess) {
        // 續(xù)租失敗，該實例未注冊，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;
    // 防止并發(fā)沖突
    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 {
        // 成功續(xù)租
        response = Response.ok().build();
    }
    logger.debug("Found (Renew): {} - {}; reply status={}", app.getName(), id, response.getStatus());
    return response;
}

AbstractInstanceRegistry#renew()

對于續(xù)租的方法，不想注冊一樣需要整個實例信息，只需要實例名稱和對應的實例id即可完成續(xù)租。

public boolean renew(String appName, String id, boolean isReplication) {
    RENEW.increment(isReplication);
    Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
    Lease<InstanceInfo> 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 {
        // 獲取實例信息
        InstanceInfo instanceInfo = leaseToRenew.getHolder();
        if (instanceInfo != null) {
            // touchASGCache(instanceInfo.getASGName());
            InstanceStatus overriddenInstanceStatus = this.getOverriddenInstanceStatus(
                    instanceInfo, leaseToRenew, isReplication);
            //  如果得到的服務實例最后狀態(tài)是UNKNOW，取消續(xù)約直接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;
            }
            // 服務狀態(tài)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);

            }
        }
        // 統(tǒng)計每分鐘續(xù)租的次數(shù)，用于自我保護機制
        renewsLastMin.increment();
        // 更新上次更新時間
        leaseToRenew.renew();
        return true;
    }
}

Lease#renew()

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

過期租約清理

在AbstractInstanceRegistry中存在EvictionTask用于定時執(zhí)行exict(0)來服務剔除，默認為60秒一次。但是如果Eureka Server處于自我保護狀態(tài)，則無法進行清理操作。在進入自我保護狀態(tài)后，在Eureka Client處，如果向Eureka Server注冊失敗，將快速超時并嘗試與其他的Eureka Server進行通信?！白晕冶Ｗo機制”的設計大大提高了Eureka的可用性。

public void evict(long additionalLeaseMs) {
    logger.debug("Running the evict task");
        // 判斷是否打開了自我保護機制
    // isLeaseExpirationEnabled == true 代表未開啟自我保護機制
    if (!isLeaseExpirationEnabled()) {
        logger.debug("DS: lease expiration is currently disabled.");
        return;
    }

    // 遍歷resgistry保存的注冊信息，用expiredLeases收集所有過期的實例信息
    List<Lease<InstanceInfo>> expiredLeases = new ArrayList<>();
    for (Entry<String, Map<String, Lease<InstanceInfo>>> groupEntry : registry.entrySet()) {
        // 對每個應用的實例列表判斷是否需要清理
        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(); // 獲取注冊的實例數(shù)
    int registrySizeThreshold = (int) (registrySize * serverConfig.getRenewalPercentThreshold()); // 獲得閾值 0.85（default）*size
    // 計算清理數(shù)量限制 evictionLimit = 
    // 注冊實例數(shù) - 注冊實例數(shù) * 0.85（default） = 0.15 * 注冊實例數(shù)
    int evictionLimit = registrySize - registrySizeThreshold; 

    // 在limit和需要清理的數(shù)量中取較小值
    int toEvict = Math.min(expiredLeases.size(), evictionLimit);
    // 存在需要清理的實例，這里使用隨機算法進行刪除
    if (toEvict > 0) {
        logger.info("Evicting {} items (expired={}, evictionLimit={})", toEvict, expiredLeases.size(), evictionLimit);

        // 用隨機算法cancel實例
        // 根據(jù)前面的保護機制，最大下線Math.min(expiredLeases.size(), evictionLimit)個實例
        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<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);
            // !! 注意，服務是逐個清理的
            internalCancel(appName, id, false);
        }
    }
}