記一次dubbo鏈接zookeeper註冊中心發生異常的排查經歷

    spring boot集成dubbo項目啓動過程當中報錯，錯誤信息以下：

2020-01-19 17:42:30.466 ERROR - [main] org.springframework.boot.SpringApplication.reportFailure(822) | Application run failed  
java.lang.IllegalStateException: zookeeper not connected  
 at org.apache.dubbo.remoting.zookeeper.curator.CuratorZookeeperClient.<init>(CuratorZookeeperClient.java:83) at org.apache.dubbo.remoting.zookeeper.curator.CuratorZookeeperTransporter.createZookeeperClient(CuratorZookeeperTransporter.java:26) at org.apache.dubbo.remoting.zookeeper.support.AbstractZookeeperTransporter.connect(AbstractZookeeperTransporter.java:68) at org.apache.dubbo.remoting.zookeeper.ZookeeperTransporter$Adaptive.connect(ZookeeperTransporter$Adaptive.java) at org.apache.dubbo.configcenter.support.zookeeper.ZookeeperDynamicConfiguration.<init>(ZookeeperDynamicConfiguration.java:70) at org.apache.dubbo.configcenter.support.zookeeper.ZookeeperDynamicConfigurationFactory.createDynamicConfiguration(ZookeeperDynamicConfigurationFactory.java:37) at org.apache.dubbo.common.config.configcenter.AbstractDynamicConfigurationFactory.lambda$getDynamicConfiguration$0(AbstractDynamicConfigurationFactory.java:39) at java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1660) at org.apache.dubbo.common.config.configcenter.AbstractDynamicConfigurationFactory.getDynamicConfiguration(AbstractDynamicConfigurationFactory.java:39) at org.apache.dubbo.common.config.configcenter.DynamicConfiguration.getDynamicConfiguration(DynamicConfiguration.java:223) at org.apache.dubbo.config.bootstrap.DubboBootstrap.prepareEnvironment(DubboBootstrap.java:815) at org.apache.dubbo.config.bootstrap.DubboBootstrap.startConfigCenter(DubboBootstrap.java:560) at org.apache.dubbo.config.bootstrap.DubboBootstrap.useRegistryAsConfigCenterIfNecessary(DubboBootstrap.java:624) at org.apache.dubbo.config.bootstrap.DubboBootstrap.initialize(DubboBootstrap.java:508) at org.apache.dubbo.config.bootstrap.DubboBootstrap.start(DubboBootstrap.java:698) at org.apache.dubbo.config.spring.context.DubboBootstrapApplicationListener.onContextRefreshedEvent(DubboBootstrapApplicationListener.java:52) at org.apache.dubbo.config.spring.context.DubboBootstrapApplicationListener.onApplicationContextEvent(DubboBootstrapApplicationListener.java:45) at org.apache.dubbo.config.spring.context.OneTimeExecutionApplicationContextEventListener.onApplicationEvent(OneTimeExecutionApplicationContextEventListener.java:40) at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172) at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165) at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139) at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:402) at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:359) at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:896) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:552) at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:743) at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:390) at org.springframework.boot.SpringApplication.run(SpringApplication.java:312) at org.springframework.boot.SpringApplication.run(SpringApplication.java:1214) at org.springframework.boot.SpringApplication.run(SpringApplication.java:1203) at cn.mogutrip.base.foundation.shell.Application.main(Application.java:28)Caused by: java.lang.IllegalStateException: zookeeper not connected  
 at org.apache.dubbo.remoting.zookeeper.curator.CuratorZookeeperClient.<init>(CuratorZookeeperClient.java:80) ... 30 common frames omitted

項目中引用的是dubbo-spring-boot-starter，版本配置以下：

<dependency>  
 <groupId>org.apache.dubbo</groupId> <artifactId>dubbo-spring-boot-starter</artifactId> <version>2.7.5</version></dependency>

    從啓動結果能夠看出，dubbo的註冊中心zookeeper鏈接不上了，起初我覺得apollo中配置的zookeeper地址錯了，覈對了一遍沒毛病。而後看了下項目中的application.properties配置文件，又看了下啓動日誌，排除了apollo沒生效的可能性。並且項目中使用的Elastic-Job的配置中心zookeeper和dubbo的同樣，可是Elastic-Job卻啓動成功了。伴隨了一頭霧水，習慣性的百度了下spring boot集成dubbo所遇到的坑，大多數的狀況是啓動類上沒有添加 @EnableDubboConfig 註解，但是個人項目添加了的。嘗試了網上的各類坑以後，仍是沒有解決。而後我讓組員在他電腦上啓動項目看一下，竟然一點問題都沒有。那就是服務器zookeeper不穩定嘍！

    但是怎麼解決這個不穩定呢？從出錯的問題更了下源碼：

能夠發現配置的信息都讀取到了的，走到下面這一步：

boolean connected = client.blockUntilConnected(timeout, TimeUnit.MILLISECONDS);

返回的值是false。若是timeout的值變大，是否是就可能爲true了呢？上面一步看出timeout=3000。那麼timeout哪裏來的，我沒發現個人配置裏有3000。

不斷跟進、跟進、跟進：

到了DubboBootstrap類的startConfigCenter方法，已經沒有入參了，這裏拿到的timeout也是3000，那就只有下面這行代碼能夠取到：

Collection<ConfigCenterConfig> configCenters = configManager.getConfigCenters();

繼續追蹤：

終於看到ConfigCenterConfig類中初始化了timeout = 3000L。原來dubbo的config-center配置中心，默認的獲取配置的超時時間是3秒鐘。

在項目的配置文件中修改一下這個時間爲10秒：

dubbo.config-center.timeout=10000

再次啓動項目，完美解決！

總結：遇到問題，仍是要從錯誤的本質出發，多跟進底層源碼，加深理解的同時，也學到了其架構思想和perfect的設計。
更多config-center的配置能夠參考連接：http://dubbo.apache.org/zh-cn...