Eureka系列(五) 服务续约流程具体实现

服务续约执行简要流程图

  下面这张图大致描述了服务续约从Client端到Server端的大致流程，详情如下：

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服务续约Client源码分析

  我们先来看看服务续约定时任务的初始化。那我们的服务续约定时任务什么时候会被初始化呢，那肯定是我们启用我们Eureka Client的时候，当我们启动Client时，Eureka会先处理相关的配置，然后初始化我们Client的相关信息，我们的定时任务也就是此时进行的初始化，具体来说我们的服务续约定时任务就是在DiscoveryClient这个类中initScheduledTasks方法中被初始化的。代码如下：

private final ScheduledExecutorService scheduler;
private void initScheduledTasks() {
     …省略其他代码
    // 初始化定时服务续约任务
    scheduler.schedule(
        new TimedSupervisorTask(
                "heartbeat",
                scheduler,
                heartbeatExecutor,
                renewalIntervalInSecs,
                TimeUnit.SECONDS,
                expBackOffBound,
                new HeartbeatThread()
        ),
        renewalIntervalInSecs, TimeUnit.SECONDS);
     …省略其他代码   
}

  由此可见，我们的定时任务其实是Client进行初始化完成的，并且还是使用ScheduledExecutorService线程池来完成我们的定时任务。接下来我们看看HeartbeatThread类相关的源码：

private class HeartbeatThread implements Runnable {
    public void run() {
        if (renew()) {
            lastSuccessfulHeartbeatTimestamp = System.currentTimeMillis();
        }
    }
}

  HeartbeatThread类中run方法调用了renew方法，我们接着看下去：

/**
* Renew with the eureka service by making the appropriate REST call
*/
boolean renew() {
    EurekaHttpResponse<InstanceInfo> httpResponse;
    try {
        // 调用Eureka Server提供的服务续约Http接口
        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();
            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;
    }
}

   通过eurekaTransport.registrationClient.sendHeartBeat(instanceInfo.getAppName(), instanceInfo.getId(), instanceInfo, null) 这行代码，我们则可以知道Client端的续约其实就是用调用Server提供的接口，然后Server端实现了服务续约的操作。

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服务续约Server源码实现

  由上面可见，我们Client的续约操作是直接调用的Server端提供的接口，以此来实现的具体操作，那我们接下来就看看Server是如何进行服务续约操作的，源码如下：

@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);
        // 进行服务续约操作
        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 = null;
        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;
    }

  由registry.renew(app.getName(), id, isFromReplicaNode);这里我们可以看到调用了renew()方法来实现续约操作，那我们就看下这个方法的实现：

Override
	public boolean renew(final String appName, final String serverId,
			boolean isReplication) {
		log("renew " + appName + " serverId " + serverId + ", isReplication {}"
				+ isReplication);
		List<Application> applications = getSortedApplications();
		for (Application input : applications) {
			if (input.getName().equals(appName)) {
				InstanceInfo instance = null;
				for (InstanceInfo info : input.getInstances()) {
					if (info.getId().equals(serverId)) {
						instance = info;
						break;
					}
				}
				publishEvent(new EurekaInstanceRenewedEvent(this, appName, serverId,
						instance, isReplication));
				break;
			}
		}
		return super.renew(appName, serverId, isReplication);
	}

  我们可以看到方法最后调用了父类的renew()方法，我们继续看下去：

public boolean renew(final String appName, final String id, final boolean isReplication) {
        if (super.renew(appName, id, isReplication)) {
            // 向其他server发送服务续约消息
            replicateToPeers(Action.Heartbeat, appName, id, null, null, isReplication);
            return true;
        }
        return false;
    }

 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(),
                                    instanceInfo.getOverriddenStatus().name(),
                                    instanceInfo.getId());
                    instanceInfo.setStatusWithoutDirty(overriddenInstanceStatus);

                }
            }
            renewsLastMin.increment();
            leaseToRenew.renew();
            return true;
        }
    }

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

  由上面的代码可见，Eureka Server服务续约的流程可大致分为以下几步：
    1.更新实例状态
    2.更新实例上次更新时间
    3.向其他Server发送服务续约消息