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。
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。
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)
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。
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:
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。
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!
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。
经过以上的过程,有3点注意: