【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:

  1. client端心跳检查调度任务
  2. 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

原创不易,如若转载 请标明来源:一枝花算不算浪漫

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,实际的服务续约的逻辑,其实就是在Lease对象中,更新一下lastUpdateTimestamp这个时间戳,每次续约,就更新一下这个时间戳就ok了。

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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【一起学源码-微服务】Nexflix Eureka 源码九:服务续约源码分析

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