阿里二面：使用 Nacos 做注冊(cè)中心怎么做優(yōu)雅發(fā)布？

作者：朱晉君 2023-06-13 08:25:14

無(wú)論是哪一款注冊(cè)中心，優(yōu)雅發(fā)布要解決的問(wèn)題都是優(yōu)雅上線和優(yōu)雅下線。本文結(jié)合 Nacos 的原理講解了 Nacos 的優(yōu)雅發(fā)布，希望對(duì)你有所幫助。

大家好，我是君哥。

今天來(lái)聊一聊使用 Nacos 做注冊(cè)中心怎么做優(yōu)雅發(fā)布。

跟其他的注冊(cè)中心一樣，Nacos 作為注冊(cè)中心的使用如下圖：

Service Provider 啟動(dòng)后注冊(cè)到 Nacos Server，Service Consumer 則從 Nacos Server 拉取服務(wù)列表，根據(jù)一定算法選擇一個(gè) Service Provider 來(lái)發(fā)送請(qǐng)求。

1.優(yōu)雅要求

對(duì)于優(yōu)雅發(fā)布，要求是 Service Provider 上線（注冊(cè)到 Nacos）后，服務(wù)能夠正常地接收和處理請(qǐng)求，而 Service Provider 停服后，則不會(huì)再收到請(qǐng)求。這就有兩個(gè)要求：

優(yōu)雅上線：Service Provider 發(fā)布完成之前，Service Consumer 不應(yīng)該從服務(wù)列表中拉取到這個(gè)服務(wù)地址；
優(yōu)雅下線：Service Provider 下線后，Service Consumer 不會(huì)從服務(wù)列表中拉取到這個(gè)服務(wù)地址。

解決了這兩個(gè)問(wèn)題，優(yōu)雅發(fā)布就可以做到了。

2.搭建環(huán)境

搭建環(huán)境是為了看 Nacos 日志，通過(guò)日志找到對(duì)應(yīng)的源代碼。本文搭建的環(huán)境如下圖：

2.1 啟動(dòng) provider

啟動(dòng) springboot-provider 的應(yīng)用，注冊(cè)到 Nacos，啟動(dòng)日志如下：

2023-06-11 18:58:10,120 [main] [INFO] com.alibaba.nacos.client.naming - [BEAT] adding beat: BeatInfo{port=8083, ip='192.168.31.94', weight=1.0, serviceName='DEFAULT_GROUP@@springboot-provider', cluster='DEFAULT', metadata={management.endpoints.web.base-path=/actuator, management.port=18082, preserved.register.source=SPRING_CLOUD, management.address=127.0.0.1}, scheduled=false, period=5000, stopped=false} to beat map.
2023-06-11 18:58:10,121 [main] [INFO] com.alibaba.nacos.client.naming - [REGISTER-SERVICE] public registering service DEFAULT_GROUP@@springboot-provider with instance: Instance{instanceId='null', ip='192.168.31.94', port=8083, weight=1.0, healthy=true, enabled=true, ephemeral=true, clusterName='DEFAULT', serviceName='null', metadata={management.endpoints.web.base-path=/actuator, management.port=18082, preserved.register.source=SPRING_CLOUD, management.address=127.0.0.1}}
2023-06-11 18:58:10,133 [main] [INFO] com.alibaba.cloud.nacos.registry.NacosServiceRegistry - nacos registry, DEFAULT_GROUP springboot-provider 192.168.31.94:8083 register finished
2023-06-11 18:58:10,221 [main] [INFO] org.springframework.boot.web.embedded.tomcat.TomcatWebServer - Tomcat initialized with port(s): 18082 (http)
2023-06-11 18:58:10,222 [main] [INFO] org.apache.coyote.http11.Http11NioProtocol - Initializing ProtocolHandler ["http-nio-127.0.0.1-18082"]
2023-06-11 18:58:10,223 [main] [INFO] org.apache.catalina.core.StandardService - Starting service [Tomcat]
2023-06-11 18:58:10,223 [main] [INFO] org.apache.catalina.core.StandardEngine - Starting Servlet engine: [Apache Tomcat/9.0.21]
2023-06-11 18:58:10,239 [main] [INFO] org.apache.catalina.core.ContainerBase.[Tomcat-1].[localhost].[/] - Initializing Spring embedded WebApplicationContext
2023-06-11 18:58:10,239 [main] [INFO] org.springframework.web.context.ContextLoader - Root WebApplicationContext: initialization completed in 99 ms
2023-06-11 18:58:10,268 [main] [INFO] org.springframework.boot.actuate.endpoint.web.EndpointLinksResolver - Exposing 22 endpoint(s) beneath base path '/actuator'
2023-06-11 18:58:10,336 [main] [INFO] org.apache.coyote.http11.Http11NioProtocol - Starting ProtocolHandler ["http-nio-127.0.0.1-18082"]
2023-06-11 18:58:10,340 [main] [INFO] org.springframework.boot.web.embedded.tomcat.TomcatWebServer - Tomcat started on port(s): 18082 (http) with context path ''
2023-06-11 18:58:10,342 [main] [INFO] boot.Application - Started Application in 7.051 seconds (JVM running for 7.874)
2023-06-11 18:58:10,358 [main] [INFO] com.alibaba.nacos.client.config.impl.ClientWorker - [fixed-39.105.183.91_8848] [subscribe] springboot-provider.properties+DEFAULT_GROUP
2023-06-11 18:58:10,359 [main] [INFO] com.alibaba.nacos.client.config.impl.CacheData - [fixed-39.105.183.91_8848] [add-listener] ok, tenant=, dataId=springboot-provider.properties, group=DEFAULT_GROUP, cnt=1
2023-06-11 18:58:10,359 [main] [INFO] com.alibaba.nacos.client.config.impl.ClientWorker - [fixed-39.105.183.91_8848] [subscribe] springboot-provider-dev.properties+DEFAULT_GROUP
2023-06-11 18:58:10,359 [main] [INFO] com.alibaba.nacos.client.config.impl.CacheData - [fixed-39.105.183.91_8848] [add-listener] ok, tenant=, dataId=springboot-provider-dev.properties, group=DEFAULT_GROUP, cnt=1
2023-06-11 18:58:10,360 [main] [INFO] com.alibaba.nacos.client.config.impl.ClientWorker - [fixed-39.105.183.91_8848] [subscribe] springboot-provider+DEFAULT_GROUP
2023-06-11 18:58:10,360 [main] [INFO] com.alibaba.nacos.client.config.impl.CacheData - [fixed-39.105.183.91_8848] [add-listener] ok, tenant=, dataId=springboot-provider, group=DEFAULT_GROUP, cnt=1
2023-06-11 18:58:10,639 [RMI TCP Connection(1)-192.168.31.94] [INFO] org.apache.catalina.core.ContainerBase.[Tomcat].[localhost].[/] - Initializing Spring DispatcherServlet 'dispatcherServlet'
2023-06-11 18:58:10,839 [com.alibaba.nacos.client.naming.updater] [INFO] com.alibaba.nacos.client.naming - [BEAT] adding beat: BeatInfo{port=8083, ip='192.168.31.94', weight=1.0, serviceName='DEFAULT_GROUP@@springboot-provider', cluster='DEFAULT', metadata={management.endpoints.web.base-path=/actuator, management.port=18082, preserved.register.source=SPRING_CLOUD, management.address=127.0.0.1}, scheduled=false, period=5000, stopped=false} to beat map.
2023-06-11 18:58:10,840 [com.alibaba.nacos.client.naming.updater] [INFO] com.alibaba.nacos.client.naming - modified ips(1) service: DEFAULT_GROUP@@springboot-provider@@DEFAULT -> [{"instanceId":"192.168.31.94#8083#DEFAULT#DEFAULT_GROUP@@springboot-provider","ip":"192.168.31.94","port":8083,"weight":1.0,"healthy":true,"enabled":true,"ephemeral":true,"clusterName":"DEFAULT","serviceName":"DEFAULT_GROUP@@springboot-provider","metadata":{"management.endpoints.web.base-path":"/actuator","management.port":"18082","preserved.register.source":"SPRING_CLOUD","management.address":"127.0.0.1"},"ipDeleteTimeout":30000,"instanceHeartBeatInterval":5000,"instanceHeartBeatTimeOut":15000}]
2023-06-11 18:58:10,841 [com.alibaba.nacos.client.naming.updater] [INFO] com.alibaba.nacos.client.naming - current ips:(1) service: DEFAULT_GROUP@@springboot-provider@@DEFAULT -> [{"instanceId":"192.168.31.94#8083#DEFAULT#DEFAULT_GROUP@@springboot-provider","ip":"192.168.31.94","port":8083,"weight":1.0,"healthy":true,"enabled":true,"ephemeral":true,"clusterName":"DEFAULT","serviceName":"DEFAULT_GROUP@@springboot-provider","metadata":{"management.endpoints.web.base-path":"/actuator","management.port":"18082","preserved.register.source":"SPRING_CLOUD","management.address":"127.0.0.1"},"ipDeleteTimeout":30000,"instanceHeartBeatInterval":5000,"instanceHeartBeatTimeOut":15000}]

我們?cè)倏聪?Nacos 的日志，這里看的文件 naming-server.log，日志如下：

2023-06-11 18:58:09,723 INFO Client connection 192.168.31.94:51885#true connect
2023-06-11 18:58:10,105 INFO Client change for service Service{namespace='public', group='DEFAULT_GROUP', name='springboot-provider', ephemeral=true, revisinotallow=1}, 192.168.31.94:8083#true
2023-06-11 18:58:18,204 INFO Client connection 192.168.31.94:60850#true disconnect, remove instances and subscribers

springboot-provider 啟動(dòng)成功后，從Nacos 管理后臺(tái)可以看到下圖：

2.2 provider 下線

服務(wù)下線后，Nacos 日志如下：

2023-06-11 19:01:03,375 INFO Client connection 192.168.31.94:51885#true disconnect, remove instances and subscribers
2023-06-11 19:01:05,048 INFO [AUTO-DELETE-IP] service: Service{namespace='public', group='DEFAULT_GROUP', name='springboot-provider', ephemeral=true, revisinotallow=2}, ip: {"ip":"192.168.31.94","port":8083,"healthy":false,"cluster":"DEFAULT","extendDatum":{"management.endpoints.web.base-path":"/actuator","management.port":"18082","preserved.register.source":"SPRING_CLOUD","management.address":"127.0.0.1","customInstanceId":"192.168.31.94#8083#DEFAULT#DEFAULT_GROUP@@springboot-provider"},"lastHeartBeatTime":1686481231604,"metadataId":"192.168.31.94:8083:DEFAULT"}
2023-06-11 19:01:05,048 INFO Client remove for service Service{namespace='public', group='DEFAULT_GROUP', name='springboot-provider', ephemeral=true, revisinotallow=2}, 192.168.31.94:8083#true
2023-06-11 19:01:08,379 INFO Client connection 192.168.31.94:8083#true disconnect, remove instances and subscribers

2.3 服務(wù)調(diào)用

在 springboot-consumer 上跑一個(gè)單元測(cè)試的用例，用 FeignClient 調(diào)用下面的方法：

@FeignClient(value = "springboot-provider", configuration = FeignMultipartSupportConfig.class)
public interface FeignAsEurekaClient {

    @PostMapping("/employee/save")
    String saveEmployeebyName(@RequestBody Employee employee);

}

日志如下：

2023-06-11 19:15:47,694 [main] [INFO] org.springframework.test.context.transaction.TransactionContext - Began transaction (1) for test context [DefaultTestContext@5bf0d49 testClass = TestFeignAsEurekaClient, testInstance = boot.service.TestFeignAsEurekaClient@10683d9d, testMethod = testPostEmployByFeign@TestFeignAsEurekaClient, testException = [null], mergedContextConfiguration = [WebMergedContextConfiguration@5b7a5baa testClass = TestFeignAsEurekaClient, locations = '{}', classes = '{class boot.Application, class boot.Application}', contextInitializerClasses = '[]', activeProfiles = '{}', propertySourceLocations = '{}', propertySourceProperties = '{org.springframework.boot.test.context.SpringBootTestCnotallow=true, server.port=0}', contextCustomizers = set[org.springframework.boot.test.context.filter.ExcludeFilterContextCustomizer@166fa74d, org.springframework.boot.test.json.DuplicateJsonObjectContextCustomizerFactory$DuplicateJsonObjectContextCustomizer@588df31b, org.springframework.boot.test.mock.mockito.MockitoContextCustomizer@0, org.springframework.boot.test.web.client.TestRestTemplateContextCustomizer@7fad8c79, org.springframework.boot.test.autoconfigure.properties.PropertyMappingContextCustomizer@0, org.springframework.boot.test.autoconfigure.web.servlet.WebDriverContextCustomizerFactory$Customizer@10b48321], resourceBasePath = 'src/main/webapp', contextLoader = 'org.springframework.boot.test.context.SpringBootContextLoader', parent = [null]], attributes = map['org.springframework.test.context.web.ServletTestExecutionListener.activateListener' -> false]]; transaction manager [org.springframework.jdbc.datasource.DataSourceTransactionManager@693676d]; rollback [true]
2023-06-11 19:15:47,941 [main] [INFO] com.netflix.config.ChainedDynamicProperty - Flipping property: springboot-provider.ribbon.ActiveConnectionsLimit to use NEXT property: niws.loadbalancer.availabilityFilteringRule.activeConnectionsLimit = 2147483647
2023-06-11 19:15:47,962 [main] [INFO] com.netflix.loadbalancer.BaseLoadBalancer - Client: springboot-provider instantiated a LoadBalancer: DynamicServerListLoadBalancer:{NFLoadBalancer:name=springboot-provider,current list of Servers=[],Load balancer stats=Zone stats: {},Server stats: []}ServerList:null
2023-06-11 19:15:47,969 [main] [INFO] com.netflix.loadbalancer.DynamicServerListLoadBalancer - Using serverListUpdater PollingServerListUpdater
2023-06-11 19:15:48,064 [main] [INFO] com.netflix.config.ChainedDynamicProperty - Flipping property: springboot-provider.ribbon.ActiveConnectionsLimit to use NEXT property: niws.loadbalancer.availabilityFilteringRule.activeConnectionsLimit = 2147483647
2023-06-11 19:15:48,064 [main] [INFO] com.netflix.loadbalancer.DynamicServerListLoadBalancer - DynamicServerListLoadBalancer for client springboot-provider initialized: DynamicServerListLoadBalancer:{NFLoadBalancer:name=springboot-provider,current list of Servers=[192.168.31.94:8083],Load balancer stats=Zone stats: {unknown=[Zone:unknown; Instance count:1; Active connections count: 0; Circuit breaker tripped count: 0; Active connections per server: 0.0;]
},Server stats: [[Server:192.168.31.94:8083; Zone:UNKNOWN; Total Requests:0; Successive connection failure:0; Total blackout seconds:0; Last connection made:Thu Jan 01 08:00:00 CST 1970; First connection made: Thu Jan 01 08:00:00 CST 1970; Active Connections:0; total failure count in last (1000) msecs:0; average resp time:0.0; 90 percentile resp time:0.0; 95 percentile resp time:0.0; min resp time:0.0; max resp time:0.0; stddev resp time:0.0]
]}ServerList:com.alibaba.cloud.nacos.ribbon.NacosServerList@24d998ba

注意，這里使用了 OpenFeign，其中用到了 Ribbon 做負(fù)載均衡，那就需要考慮到 Ribbon 的刷新本地服務(wù)列表的時(shí)間，從源代碼中看，刷新周期是 30s。如下圖：

Ribbon 刷新緩存的邏輯參考下面代碼：

public synchronized void start(final UpdateAction updateAction) {
 if (isActive.compareAndSet(false, true)) {
  final Runnable wrapperRunnable = new Runnable() {
   @Override
   public void run() {
    //...
   }
  };

  scheduledFuture = getRefreshExecutor().scheduleWithFixedDelay(
    wrapperRunnable,
    initialDelayMs,
    refreshIntervalMs,//這里定義的是30s
    TimeUnit.MILLISECONDS
  );
 }//...
}

3.優(yōu)雅發(fā)布

前面第一節(jié)提到過(guò)，優(yōu)雅發(fā)布有兩個(gè)要求：優(yōu)雅上線和優(yōu)雅下線。

Nacos 客戶(hù)端和服務(wù)端的交互采用長(zhǎng)輪詢(xún)的方式，服務(wù)端收到客戶(hù)端的請(qǐng)求后，首先會(huì)判斷服務(wù)端本地的服務(wù)列表是否跟客戶(hù)端的相比是否發(fā)生變化（比較 MD5），如果發(fā)生變化則立即通知客戶(hù)端，否則放入長(zhǎng)輪詢(xún)隊(duì)列掛起，如果這段時(shí)間內(nèi)服務(wù)列表發(fā)生變化，則立刻通知客戶(hù)端，否則等到超時(shí)后再通知客戶(hù)端。代碼如下：

//LongPollingService.java
public void addLongPollingClient(HttpServletRequest req, HttpServletResponse rsp, Map<String, String> clientMd5Map,
  int probeRequestSize) {
 
 String str = req.getHeader(LongPollingService.LONG_POLLING_HEADER);
 int delayTime = SwitchService.getSwitchInteger(SwitchService.FIXED_DELAY_TIME, 500);
 
 // Add delay time for LoadBalance, and one response is returned 500 ms in advance to avoid client timeout.
 long timeout = -1L;
 if (isFixedPolling()) {
  //...
 } else {
  timeout = Math.max(10000, Long.parseLong(str) - delayTime);//29.5s
  long start = System.currentTimeMillis();
  List<String> changedGroups = MD5Util.compareMd5(req, rsp, clientMd5Map);
  if (changedGroups.size() > 0) {
      //服務(wù)列表發(fā)生變化，直接返回給客戶(hù)端
   generateResponse(req, rsp, changedGroups);
   return;
  } //...
 }
 String ip = RequestUtil.getRemoteIp(req);
 //..
 
 // Must be called by http thread, or send response.
 final AsyncContext asyncContext = req.startAsync();
 // AsyncContext.setTimeout() is incorrect, Control by oneself
 asyncContext.setTimeout(0L);
 
 String appName = req.getHeader(RequestUtil.CLIENT_APPNAME_HEADER);
 String tag = req.getHeader("Vipserver-Tag");
 //服務(wù)列表沒(méi)有發(fā)生變化，放入長(zhǎng)輪詢(xún)隊(duì)列等待調(diào)度
 ConfigExecutor.executeLongPolling(
   new ClientLongPolling(asyncContext, clientMd5Map, ip, probeRequestSize, timeout, appName, tag));
}

從上面服務(wù)端源代碼可以看到，這里超時(shí)時(shí)間是 30s，其中 29.5s 用于掛起等待，0.5s 檢查服務(wù)列表是否發(fā)生變化。這里使用了長(zhǎng)輪詢(xún)，如果服務(wù)端列表發(fā)生變化，會(huì)立刻通知客戶(hù)端，所以對(duì)優(yōu)雅發(fā)布影響非常小。

服務(wù)列表發(fā)生變化后，客戶(hù)端用單獨(dú)的線程通知監(jiān)聽(tīng)的 listener，代碼如下：

public void startInternal() {
 executor.schedule(() -> {
  while (!executor.isShutdown() && !executor.isTerminated()) {
   try {
    listenExecutebell.poll(5L, TimeUnit.SECONDS);
    //...
    executeConfigListen();
   } catch (Throwable e) {
    //...
   }
  }
 }, 0L, TimeUnit.MILLISECONDS);
 
}

3.1 優(yōu)雅上線

優(yōu)雅上線存在的問(wèn)題主要在于 Service Provider 注冊(cè)到 Nacos 后，服務(wù)還沒(méi)有完成初始化，請(qǐng)求已經(jīng)到來(lái)。這種情況主要原因是 Service Provider 啟動(dòng)后立刻注冊(cè) Naocs，而本身提供的接口可能還沒(méi)有初始化完成。

這種情況的解決方法是關(guān)閉自動(dòng)注冊(cè)：

spring.cloud.nacos.discovery.registerEnabled=false

在服務(wù)初始化后使用代碼手動(dòng)注冊(cè)，代碼如下：

Properties setting8 = new Properties();
String serverIp8 = "127.0.0.1:8848";
setting8.put(PropertyKeyConst.SERVER_ADDR, serverIp8);
setting8.put(PropertyKeyConst.USERNAME, "nacos");
setting8.put(PropertyKeyConst.PASSWORD, "nacos");
NamingService inaming8 = NacosFactory.createNamingService(setting7);
inaming8.registerInstance("springboot-provider", "192.168.31.94", 8083);

3.2 優(yōu)雅下線

服務(wù)下線分兩種情況，一個(gè)是正常停服，一個(gè)是服務(wù)故障。

3.2.1 正常停服

對(duì)于正常停服，Nacos 采用心跳檢測(cè)來(lái)實(shí)現(xiàn)服務(wù)在線。心跳周期是 5s，Nacos Server 如果 15s 沒(méi)收到心跳就會(huì)將實(shí)例設(shè)置為不健康，在 30s 沒(méi)收到心跳才會(huì)講這個(gè)服務(wù)刪除。當(dāng)然這個(gè)時(shí)間可以設(shè)置：

spring.cloud.nacos.discovery.metadata.preserved.heart.beat.interval=1000 #心跳間隔5s->1s
spring.cloud.nacos.discovery.metadata.preserved.heart.beat.timeout=3000 #超時(shí)時(shí)間15s->3s
spring.cloud.nacos.discovery.metadata.preserved.ip.delete.timeout=5000 #刪除時(shí)間30s->5s

但這樣并不能保證服務(wù)停止后能夠立刻從 Nacos Server 下線，很有可能服務(wù)停止后還能再收到請(qǐng)求，最好的方式是手動(dòng)下線，比如增加一個(gè) API 接口，服務(wù)下線之前增加 preStopHook 函數(shù)調(diào)用這個(gè) API 接口來(lái)實(shí)現(xiàn)下線。API 接口示例代碼如下：

@GetMapping(value = "/nacos/deregisterInstance")
public String deregisterInstance() {
 Properties prop = new Properties();
 prop.setProperty("serverAddr", "localhost");
 prop.put(PropertyKeyConst.NAMESPACE, "test");
 NacosNamingService client = new NacosNamingService(prop);
 client.deregisterInstance("springboot-provider", "192.168.31.94", 8083);
 return "success";
}

在使用 Ribbon 的場(chǎng)景，也需要考慮 Ribbon 更新本地緩存服務(wù)列表的機(jī)制，手動(dòng)下線后，可以再等待 30s 再關(guān)閉服務(wù)。

3.2.1 服務(wù)故障

第二種情況是服務(wù)故障，但是并沒(méi)有停服，這種情況是很難避免外部請(qǐng)求再發(fā)送過(guò)來(lái)的。處理方式是對(duì)這個(gè)服務(wù)本身的健康檢查結(jié)果進(jìn)行處理，比如連續(xù)三次健康檢查失敗，可以調(diào)用上面的 API 接口讓服務(wù)下線。