<返回更多

Dubbo + Nacos这么玩就失去高可用的能力了

2023-09-08  微信公众号  不焦躁的程序员
加入收藏

我们常用的微服务框架是SpringCloud那一套，在服务远程调用和注册中心的选型上也有不少方案。在服务远程调用上常用的有：Feign、Dubbo等，在注册中心上常用的有：Nacos、Zookeeper、Consul、Eureka等。我们项目这两块的选型是这样的：RPC调用-Dubbo、注册中心和配置中心-Nacos。

一、故障开端

项目平稳运行了好几年，有一天发现Nacos集群的Server内存有点高，所以想升级下机器配置，然后重启。说干就干，立马在测试环境的3台Nacos-Server集群中，任意选了一台进行停机，暂且叫它Nacos-Server-1吧。接下来就是故障了开端了。

停机之后，测试环境立马有许多服务的接口调不通，等待许久，故障一直没恢复。所以又赶紧把Nacos-Server-1启动起来。要找找原因，否则无法在生产环境重启Nacos-Server。

我一直的观点是：出现疑难问题时，首先看异常信息，然后猜测原因，再通过实践去验证，最终可以通过源码再去证实。而不是一上来就看源码，那样比酱香配拿铁更伤头。

二、、异常信息

当Nacos-server-1停机时，首先在Nacos-Client（即某个微服务应用）看到异常，主要有2个：

(1) nacos-client与nacos-server心跳异常：

2023-09-06 08:10:09|ERROR|com.alibaba.nacos.client.naming.NET.NamingProxy:reqApi|548|com.alibaba.nacos.naming.beat.sender|"request: /nacos/v1/ns/instance/beat failed, servers: [10.20.1.13:8848, 10.20.1.14:8848, 10.20.1.15:8848], code: 500, msg: JAVA.net.SocketTimeoutException: Read timed out"|""
2023-09-06 08:10:09|ERROR|com.alibaba.nacos.client.naming.beat.BeatReactor$BeatTask:run|198|com.alibaba.nacos.naming.beat.sender|"[CLIENT-BEAT] failed to send beat: {"port":0,"ip":"10.21.230.14","weight":1.0,"serviceName":"DEFAULT_GROUP@@consumers:com.cloud.usercenter.api.PartyCompanyMemberApi:1.0:","metadata":{"owner":"ehome-cloud-owner","init":"false","side":"consumer","Application.version":"1.0","methods":"queryGroupMemberCount,queryWithValid,query,queryOne,update,insert,queryCount,queryPage,delete,queryList","release":"2.7.8","dubbo":"2.0.2","pid":"6","check":"false","interface":"com.bm001.ehome.cloud.usercenter.api.PartyCompanyMemberApi","version":"1.0","qos.enable":"false","timeout":"20000","revision":"1.2.38-SNAPSHOT","retries":"0","path":"com.bm001.ehome.cloud.usercenter.api.PartyCompanyMemberApi","protocol":"consumer","metadata-type":"remote","application":"xxxx-cloud","sticky":"false","category":"consumers","timestamp":"1693917779436"},"scheduled":false,"period":5000,"stopped":false}, code: 500, msg: failed to req API:/nacos/v1/ns/instance/beat after all servers([10.20.1.13:8848, 10.20.1.14:8848, 10.20.1.15:8848])"|""
2023-09-06 08:10:10|ERROR|com.alibaba.nacos.client.naming.net.NamingProxy:callServer|613|com.alibaba.nacos.naming.beat.sender|"[NA] failed to request"|"com.alibaba.nacos.api.exception.NacosException: java.net.ConnectException: 拒绝连接 (Connection refused)
        at com.alibaba.nacos.client.naming.net.NamingProxy.callServer(NamingProxy.java:611)
        at com.alibaba.nacos.client.naming.net.NamingProxy.reqApi(NamingProxy.java:524)
        at com.alibaba.nacos.client.naming.net.NamingProxy.reqApi(NamingProxy.java:491)
        at com.alibaba.nacos.client.naming.net.NamingProxy.sendBeat(NamingProxy.java:426)
        at com.alibaba.nacos.client.naming.beat.BeatReactor$BeatTask.run(BeatReactor.java:167)
        
Caused by: java.io.IOException: Server returned HTTP response code: 502 for URL: http://10.20.1.14:8848/nacos/v1/ns/instance/beat?app=unknown&serviceName=DEFAULT_GROUP%40%40providers%3AChannelOrderExpressApi%3A1.0%3A&namespaceId=dev&port=20880&ip=10.20.0.200
  at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1914)
  at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1512)
  at java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:480)
  at com.alibaba.nacos.common.http.client.response.JdkHttpClientResponse.getStatusCode(JdkHttpClientResponse.java:75)
  at com.alibaba.nacos.common.http.client.handler.AbstractResponseHandler.handle(AbstractResponseHandler.java:43)
"

(2) dubbo微服务调用异常：

2023-09-06 08:09:38|ERROR|runtimeExceptionHandler|135|http-nio-8080-exec-5|"发生系统异常"|"org.Apache.dubbo.rpc.RpcException: No provider available from registry 10.20.1.13:8848,10.20.1.14:8848,10.20.1.15:8848 for service ClueAuntMatchApi:1.0 on consumer 10.21.230.14 use dubbo version 2.7.8, please check status of providers(disabled, not registered or in blacklist).
        at org.apache.dubbo.registry.integration.RegistryDirectory.doList(RegistryDirectory.java:599)
        at org.apache.dubbo.rpc.cluster.directory.AbstractDirectory.list(AbstractDirectory.java:74)
        at org.apache.dubbo.rpc.cluster.support.AbstractClusterInvoker.list(AbstractClusterInvoker.java:292)
        at org.apache.dubbo.rpc.cluster.support.AbstractClusterInvoker.invoke(AbstractClusterInvoker.java:257)
        at org.apache.dubbo.rpc.cluster.interceptor.ClusterInterceptor.intercept(ClusterInterceptor.java:47)

三、根据异常进行猜测

熟悉Dubbo的朋友肯定知道这个错误please check status of providers(disabled, not registered or in blacklist).，基本上是代表：Provider下线了 或者 Consumer没找到Provider。

根据以往使用dubbo + zookeeper的经验，客户端应该会拉取注册中心的Provider的信息，然后本地缓存一份，即使注册中心挂了，应该也能调用到别的服务。不至于出现完全找不到服务提供者的信息。

当思考不出来时，只能靠异常去猜测原因了。根据以上2个异常开始猜测。

1.猜测1

由于nacos-server-1挂了，导致nacos-client与server的心跳异常，导致本地缓存的provider的元数据被清掉了。有了猜测，赶紧查看nacos-client的源代码，找到nacos-client 与 nacos-server 心跳的那一段：

图片

继续往下跟，可以看到这段核心代码：

public String reqApi(String api, Map<String, String> params, Map<String, String> body, List<String> servers,
            String method) throws NacosException {
        params.put(CommonParams.NAMESPACE_ID, getNamespaceId());
        if (CollectionUtils.isEmpty(servers) && StringUtils.isEmpty(nacosDomain)) {
            throw new NacosException(NacosException.INVALID_PARAM, "no server available");
        }
        NacosException exception = new NacosException();
        if (servers != null && !servers.isEmpty()) {
            Random random = new Random(System.currentTimeMillis());
            int index = random.nextInt(servers.size());
            
            for (int i = 0; i < servers.size(); i++) {
                String server = servers.get(index);
                try {
                    return callServer(api, params, body, server, method);
                } catch (NacosException e) {
                    exception = e;
                    if (NAMING_LOGGER.isDebugEnabled()) {
                        NAMING_LOGGER.debug("request {} failed.", server, e);
                    }
                }
                index = (index + 1) % servers.size();
            }
        }
        
        if (StringUtils.isNotBlank(nacosDomain)) {
            for (int i = 0; i < UtilAndComs.REQUEST_DOMAIN_RETRY_COUNT; i++) {
                try {
                    return callServer(api, params, body, nacosDomain, method);
                } catch (NacosException e) {
                    exception = e;
                    if (NAMING_LOGGER.isDebugEnabled()) {
                        NAMING_LOGGER.debug("request {} failed.", nacosDomain, e);
                    }
                }
            }
        }
        NAMING_LOGGER.error("request: {} failed, servers: {}, code: {}, msg: {}", api, servers, exception.getErrCode(),
                exception.getErrMsg());
        throw new NacosException(exception.getErrCode(),
                "failed to req API:" + api + " after all servers(" + servers + ") tried: " + exception.getMessage());
    }

注意上面的这段代码：

for (int i = 0; i < servers.size(); i++) {
    String server = servers.get(index);
    try {
        return callServer(api, params, body, server, method);
    } catch (NacosException e) {
        exception = e;
        if (NAMING_LOGGER.isDebugEnabled()) {
            NAMING_LOGGER.debug("request {} failed.", server, e);
        }
    }
    index = (index + 1) % servers.size();
}

通过以上这一段代码可以知道，nacos-client与nacos-server集群里的随机一台通信，感兴趣的朋友可以继续阅读源代码，跟到最后会发现，只要有一次心跳是正常的，那就认为心跳正常。因为我只停了一台nacos-server，但是与其他两台server依旧可以保持心跳，所以整个心跳过程虽然报错，但是仍然是正常的，所以这个猜测放弃了，继续猜测。

2.猜测2

既然dubbo与zookeeper是建立长连接进行socket通信，那dubbo与nacos-server可能也是建立了长连接进行socket通信，某个nacos-server挂了之后，可能因为nacos-server没有zookeeper的选主机制，所以不会自动切换到别的可用的nacos-server去调用。

或者是nacos-server集群选主问题，选主后没有及时通知到consumer，或者consumer与nacos本身通信机制有问题。总之就是因为某种机制，导致没有自动切换到可用的nacos-server上，导致获取不到provider元数据，自然就无法发起调用。

既然有了这个猜想，那就赶紧去证实：

继续翻看nacos源码，发现nacos提供了集群节点之间数据一致性保障，使用的是Raft协议（一致性的选主协议，最后在简单介绍），源代码如下：

既然有选主协议，那就看看为什么通信还是失败了呢？继续从nacos-server的异常信息入手，在nacos-server-1停机时，看到nacos-server的logs下多种异常信息：

在naming-raft.log里，如下异常信息：

java.lang.NullPointerException: null
  at com.alibaba.nacos.naming.consistency.persistent.raft.RaftCore.signalDelete(RaftCore.java:275)
  at com.alibaba.nacos.naming.consistency.persistent.raft.RaftConsistencyServiceImpl.remove(RaftConsistencyServiceImpl.java:72)
  at com.alibaba.nacos.naming.consistency.DelegateConsistencyServiceImpl.remove(DelegateConsistencyServiceImpl.java:53)
  at com.alibaba.nacos.naming.core.ServiceManager.easyRemoveService(ServiceManager.java:434)
  at com.alibaba.nacos.naming.core.ServiceManager$EmptyServiceAutoClean.lambda$null$1(ServiceManager.java:902)
  at java.util.concurrent.ConcurrentHashMap.computeIfPresent(ConcurrentHashMap.java:1769)
  at com.alibaba.nacos.naming.core.ServiceManager$EmptyServiceAutoClean.lambda$null$2(ServiceManager.java:891)
  at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183)
  at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:175)
  at java.util.concurrent.ConcurrentHashMap$EntrySpliterator.forEachRemaining(ConcurrentHashMap.java:3606)
  at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
  at java.util.stream.ForEachOps$ForEachTask.compute(ForEachOps.java:290)
  at java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:731)
  at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
  at java.util.concurrent.ForkJoinPool.helpComplete(ForkJoinPool.java:1870)
  at java.util.concurrent.ForkJoinPool.externalHelpComplete(ForkJoinPool.java:2467)
  at java.util.concurrent.ForkJoinTask.externalAwaitDone(ForkJoinTask.java:324)
  at java.util.concurrent.ForkJoinTask.doInvoke(ForkJoinTask.java:405)
  at java.util.concurrent.ForkJoinTask.invoke(ForkJoinTask.java:734)
  at java.util.stream.ForEachOps$ForEachOp.evaluateParallel(ForEachOps.java:159)
  at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateParallel(ForEachOps.java:173)
  at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:233)
  at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:485)
  at com.alibaba.nacos.naming.core.ServiceManager$EmptyServiceAutoClean.lambda$run$3(ServiceManager.java:891)
  at java.util.concurrent.ConcurrentHashMap.forEach(ConcurrentHashMap.java:1597)
  at com.alibaba.nacos.naming.core.ServiceManager$EmptyServiceAutoClean.run(ServiceManager.java:881)
  at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
  at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
  at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
  at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
  at java.lang.Thread.run(Thread.java:748)
2023-09-07 08:19:25,262 ERROR Raft remove failed.

naming-push.log里，如下异常信息：

java.lang.IllegalStateException: unable to find ackEntry for key: 10.21.140.23,43998,31247629183519634, ack json: {"type": "push-ack", "lastRefTime":"31247629183519634", "data":""}
  at com.alibaba.nacos.naming.push.PushService$Receiver.run(PushService.java:677)
  at java.lang.Thread.run(Thread.java:748)
2023-09-07 08:17:38,533 ERROR [NACOS-PUSH] error while receiving ack data

naming-distro.log里，如下异常信息：

2023-09-07 08:19:39,904 ERROR receive responsible key timestamp of com.alibaba.nacos.naming.iplist.ephemeral.dev-jzj##DEFAULT_GROUP@@providers:com.bm001.league.ordercenter.api.AdCluePoolApi:1.0: from 10.20.1.13:8848

将这些异常信息结合起来可以推断出，在nacos-server-1停机时，nacos-server集群只剩余2台机器，它们在利用Raft协议进行选主时，出现了异常。导致consumer没有找到主节点，无法建立正确的通信，所以consumer获取不到provider的元数据。

继续证实这个推断吧！

此时同时把nacos-server-1和nacos-server-2同时停机，只保留1台nacos-server时，微服务之间调用就正常了。因为单个节点时，选主正常，consumer很快与nacos-server建立了通信。此时再把3台全部启动后，也是一切正常。至此可以证实2台nacos-server确实存在选主问题。

至此问题解决，安心干活儿去了，哈哈！

3.Raft协议

简单讲下Raft协议，Raft协议主要用来满足微服务CAP理论中的CP，保障集群环境下的数据一致性。在Raft理论中，把每一个集群节点定义了三种状态，跟zookeeper的ZAB 协议类似：

Follower 追随者：集群所有节点一开始都是 Follower。

Candidate 候选者：当集群的某个节点开始发起投票选举 Leader 的时，先给自己投一票，这时就会从 Follower 变成 Candidate。

Leader 领导者：当集群的某个节点获得大多数节点（超过一半）的投票，那么就会变成 Leader。

四、总结

经过以上的过程，有3点注意：

关键词：Dubbo      点击(13)
声明：本站部分内容来自互联网,如有版权侵犯或其他问题请与我们联系，我们将立即删除或处理。
▍相关推荐
更多Dubbo相关>>>
Copyright @ 简易百科 V 2.0 京ICP备14042104号