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： 
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。
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
