Eureka 續約 (心跳檢測)

心跳，eureka client每隔一定的時間，會給eureka server傳送心跳，保持心跳，讓eureka server知道自己還活著，lease renewal，續約，心跳.

Eureka-Client 向 Eureka-Server 發起註冊應用例項成功後獲得租約 ( Lease )。
Eureka-Client 固定間隔向 Eureka-Server 發起續租( renew )，避免租約過期。

預設情況下，租約有效期為 90 秒，續租頻率為 30 秒。兩者比例為 1 : 3 ，保證在網路異常等情況下，有三次重試的機會。

（1）DiscoveryClient初始化的時候，會去排程一堆定時任務，其中有一個就是HeartbeatThread，心跳執行緒

（2）在這裡可以看到，預設是每隔30秒去傳送一次心跳，每隔30秒執行一次HeartbeatTHread執行緒的邏輯，傳送心跳

（3）這邊的話就是去傳送這個心跳，走的是EurekaHttpClient的sendHeartbeat()方法，http://localhost:8080/v2/apps/ServiceA/i-000000-1，走的是put請求

    /**
     * The heartbeat task that renews the lease in the given intervals.
     */
    private class HeartbeatThread implements Runnable {

        public void run() {
            if (renew()) {
                lastSuccessfulHeartbeatTimestamp = System.currentTimeMillis();
            }
        }
    }

    /**
     * Renew with the eureka service by making the appropriate REST call
     */
    boolean renew() {
        EurekaHttpResponse<InstanceInfo> httpResponse;
        try {
            httpResponse = eurekaTransport.registrationClient.sendHeartBeat(instanceInfo.getAppName(), instanceInfo.getId(), instanceInfo, null);
            logger.debug(PREFIX + "{} - Heartbeat status: {}", appPathIdentifier, httpResponse.getStatusCode());
            if (httpResponse.getStatusCode() == Status.NOT_FOUND.getStatusCode()) {
                REREGISTER_COUNTER.increment();
                logger.info(PREFIX + "{} - Re-registering apps/{}", appPathIdentifier, instanceInfo.getAppName());
                long timestamp = instanceInfo.setIsDirtyWithTime();
                boolean success = register();
                if (success) {
                    instanceInfo.unsetIsDirty(timestamp);
                }
                return success;
            }
            return httpResponse.getStatusCode() == Status.OK.getStatusCode();
        } catch (Throwable e) {
            logger.error(PREFIX + "{} - was unable to send heartbeat!", appPathIdentifier, e);
            return false;
        }
    }
 

（4）負責承接服務例項的心跳相關的這些操作的，是ApplicationsResource，服務相關的controller。找到ApplicationResource，再次找到InstanceResource，通過PUT請求，可以找到renewLease方法。

    @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);
        boolean isSuccess = registry.renew(app.getName(), id, isFromReplicaNode);

        // Not found in the registry, immediately ask for a register
        if (!isSuccess) {
            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;
        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 {
            response = Response.ok().build();
        }
        logger.debug("Found (Renew): {} - {}; reply status={}", app.getName(), id, response.getStatus());
        return response;
    }
 

（5）通過登錄檔的renew()方法，進去完成服務續約，實際進入AbstractInstanceRegistry的renew()方法

    /**
     * Marks the given instance of the given app name as renewed, and also marks whether it originated from
     * replication.
     *
     * @see com.netflix.eureka.lease.LeaseManager#renew(java.lang.String, java.lang.String, boolean)
     */
    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 {
            InstanceInfo instanceInfo = leaseToRenew.getHolder();
            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(),
                                    overriddenInstanceStatus.name(),
                                    instanceInfo.getId());
                    instanceInfo.setStatusWithoutDirty(overriddenInstanceStatus);

                }
            }
            // 新增 續租每分鐘次數
            renewsLastMin.increment();
            // 設定 租約最後更新時間（續租）
            leaseToRenew.renew();
            return true;
        }
    }

實際的服務續約的邏輯，其實就是在Lease物件中，更新一下lastUpdateTimestamp這個時間戳，每次續約，就更新一下,duration這裡加了一遍，也是eureka的bug，但是官網並不做修改。

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