【一起学源码-微服务】Nexflix Eureka 源码九:服务续约源码分析
前言
前情回顾
上一讲 我们讲解了服务发现的相关逻辑,所谓服务发现 其实就是注册表抓取,服务实例默认每隔30s去注册中心抓取一下注册表增量数据,然后合并本地注册表数据,最后有个hash对比的操作。
本讲目录
今天主要是看下服务续约的逻辑,服务续约就是client端给server端发送心跳检测,告诉对方我还活着。现在很多分布式系统都会有心跳检查的机制,这里一起来学习下Eureka是怎么做心跳检查的。
目录如下:
- client端心跳检查调度任务
- server端接收心跳检查,设置最后renew时间
这一讲内容不太多,因为上一篇文章写全量和增量注册表信息内容有点多,所以这里将博客尽量一篇保持一个知识点,后面还会讲服务实例下线、摘除、注册中心自我保护等机制的实现原理。
说明
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源码分析
client端心跳检查调度任务
服务实例续约代码比较简单,这里还是从DiscovertClient.java
开始,很多源码的入口都是在这里,因为client端初始化、注册 都是走的这里,因为前几篇文章对这个类已经分析很多了,这里只截取部分重要代码:
DiscovertClient.java
初始化后 会继续初始化一些调度任务:
private void initScheduledTasks() {
if (clientConfig.shouldRegisterWithEureka()) {
// 默认也是30s
int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
logger.info("Starting heartbeat executor: " + "renew interval is: " + renewalIntervalInSecs);
// Heartbeat timer
// 执行heartbeatExecutor心跳检查,默认是30s
scheduler.schedule(
new TimedSupervisorTask(
"heartbeat",
scheduler,
heartbeatExecutor,
renewalIntervalInSecs,
TimeUnit.SECONDS,
expBackOffBound,
new HeartbeatThread()
),
renewalIntervalInSecs, TimeUnit.SECONDS);
// 执行线程
instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
} else {
logger.info("Not registering with Eureka server per configuration");
}
}
private class HeartbeatThread implements Runnable {
public void run() {
if (renew()) {
lastSuccessfulHeartbeatTimestamp = System.currentTimeMillis();
}
}
}
boolean renew() {
EurekaHttpResponse<InstanceInfo> httpResponse;
try {
httpResponse = eurekaTransport.registrationClient.sendHeartBeat(instanceInfo.getAppName(), instanceInfo.getId(), instanceInfo, null);
logger.debug("{} - Heartbeat status: {}", PREFIX + appPathIdentifier, httpResponse.getStatusCode());
if (httpResponse.getStatusCode() == 404) {
REREGISTER_COUNTER.increment();
logger.info("{} - Re-registering apps/{}", PREFIX + 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("{} - was unable to send heartbeat!", PREFIX + appPathIdentifier, e);
return false;
}
}
public EurekaHttpResponse<InstanceInfo> sendHeartBeat(String appName, String id, InstanceInfo info, InstanceStatus overriddenStatus) {
String urlPath = "apps/" + appName + '/' + id;
Response response = null;
try {
WebTarget webResource = jerseyClient.target(serviceUrl)
.path(urlPath)
.queryParam("status", info.getStatus().toString())
.queryParam("lastDirtyTimestamp", info.getLastDirtyTimestamp().toString());
if (overriddenStatus != null) {
webResource = webResource.queryParam("overriddenstatus", overriddenStatus.name());
}
Builder requestBuilder = webResource.request();
addExtraProperties(requestBuilder);
addExtraHeaders(requestBuilder);
requestBuilder.accept(MediaType.APPLICATION_JSON_TYPE);
response = requestBuilder.put(Entity.entity("{}", MediaType.APPLICATION_JSON_TYPE)); // Jersey2 refuses to handle PUT with no body
EurekaHttpResponseBuilder<InstanceInfo> eurekaResponseBuilder = anEurekaHttpResponse(response.getStatus(), InstanceInfo.class).headers(headersOf(response));
if (response.hasEntity()) {
eurekaResponseBuilder.entity(response.readEntity(InstanceInfo.class));
}
return eurekaResponseBuilder.build();
} finally {
if (logger.isDebugEnabled()) {
logger.debug("Jersey2 HTTP PUT {}/{}; statusCode={}", serviceUrl, urlPath, response == null ? "N/A" : response.getStatus());
}
if (response != null) {
response.close();
}
}
}
这里的流程很简单,初始化DiscoveryClient
后会新建一个调度任务,然后执行HeartbeatThread
中的run方法,默认是renewalIntervalInSecs
30s执行一次。
具体就是给Server端发送一个http请求,类似于:http://localhost:8080/v2/apps/ServiceA/i-000000-1
, 走的是put请求。
最后拿到响应结果,续约成功后会更新lastSuccessfulHeartbeatTimestamp
最近成功心跳检测的时间戳。
server端接收心跳检查请求
前几篇文章已经说过,Server端接收http请求的入口在eureka-core
模块下的 resource
包里面,这里直接找到ApplicationResource.java
中的getInstanceInfo
方法,这里直接请求的InstanceResource
类的构造方法,找到这个方法中的@PUT
请求。可以直接看下代码:
InstanceResource.renewLease
+AbstractInstanceRegistry.renew
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);
// 省略部分代码
logger.debug("Found (Renew): {} - {}; reply status={}" + app.getName(), id, response.getStatus());
return response;
}
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)) {
Object[] args = {
instanceInfo.getStatus().name(),
instanceInfo.getOverriddenStatus().name(),
instanceInfo.getId()
};
logger.info(
"The instance status {} is different from overridden instance status {} for instance {}. "
+ "Hence setting the status to overridden status", args);
instanceInfo.setStatusWithoutDirty(overriddenInstanceStatus);
}
}
renewsLastMin.increment();
leaseToRenew.renew();
return true;
}
}
这里主要看renew
方法, 这里看到registry
是一个注册表,通过appName获取对应的服务注册表信息。
这里主要还是看leaseToRenew.renew()
其实很简单,就是设置当前示例注册表的renew属性的lastUpdateTimestamp
为最新时间+duration。
至于这里的duration 我们下一讲会详细讲解,duration 和服务实例摘除有关。
总结
(1)DiscoveryClient初始化的时候,会去调度一堆定时任务,其中有一个就是HeartbeatThread,心跳线程
(2)在这里可以看到,默认是每隔30秒去发送一次心跳,每隔30秒执行一次HeartbeatTHread线程的逻辑,发送心跳
(3)这边的话就是去发送这个心跳,走的是EurekaHttpClient的sendHeartbeat()方法,http://localhost:8080/v2/apps/ServiceA/i-000000-1,走的是put请求
(4)负责承接服务实例的心跳相关的这些操作的,是ApplicationsResource,服务相关的controller。找到ApplicationResource,再次找到InstanceResource,通过PUT请求,可以找到renewLease方法。
(5)通过注册表的renew()方法,进去完成服务续约,实际进入AbstractInstanceRegistry的renew()方法
(6)从注册表的map中,根据服务名和实例id,获取一个Lease
申明
本文章首发自本人博客:https://www.cnblogs.com/wang-meng 和公众号:壹枝花算不算浪漫,如若转载请标明来源!
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