一、问题分析和代码跟踪
原来跑的好好的代码，晚上运行的时候提示连接不上 zookeeper。提示信息如下：
java.lang.IllegalStateException: zookeeper not connectedat org.apache.dubbo.remoting.zookeeper.curator.CuratorZookeeperClient.<init>(CuratorZookeeperClient.java:83) ~[dubbo-2.7.7.jar:2.7.7]at org.apache.dubbo.remoting.zookeeper.curator.CuratorZookeeperTransporter.createZookeeperClient(CuratorZookeeperTransporter.java:26) ~[dubbo-2.7.7.jar:2.7.7]at org.apache.dubbo.remoting.zookeeper.support.AbstractZookeeperTransporter.connect(AbstractZookeeperTransporter.java:70) ~[dubbo-2.7.7.jar:2.7.7]at org.apache.dubbo.remoting.zookeeper.ZookeeperTransporter$Adaptive.connect(ZookeeperTransporter$Adaptive.java) ~[dubbo-2.7.7.jar:2.7.7]at org.apache.dubbo.metadata.store.zookeeper.ZookeeperMetadataReport.<init>(ZookeeperMetadataReport.java:61) ~[dubbo-2.7.7.jar:2.7.7]at org.apache.dubbo.metadata.store.zookeeper.ZookeeperMetadataReportFactory.createMetadataReport(ZookeeperMetadataReportFactory.java:37) ~[dubbo-2.7.7.jar:2.7.7]at org.apache.dubbo.metadata.report.support.AbstractMetadataReportFactory.getMetadataReport(AbstractMetadataReportFactory.java:49) ~[dubbo-2.7.7.jar:2.7.7]at org.apache.dubbo.metadata.report.MetadataReportFactory$Adaptive.getMetadataReport(MetadataReportFactory$Adaptive.java) ~[dubbo-2.7.7.jar:2.7.7]at org.apache.dubbo.metadata.report.MetadataReportInstance.init(MetadataReportInstance.java:49) ~[dubbo-2.7.7.jar:2.7.7]at org.apache.dubbo.config.bootstrap.DubboBootstrap.startMetadataReport(DubboBootstrap.java:630) ~[dubbo-2.7.7.jar:2.7.7]at org.apache.dubbo.config.bootstrap.DubboBootstrap.initMetadataService(DubboBootstrap.java:716) ~[dubbo-2.7.7.jar:2.7.7]at org.apache.dubbo.config.bootstrap.DubboBootstrap.initialize(DubboBootstrap.java:517) ~[dubbo-2.7.7.jar:2.7.7]at org.apache.dubbo.config.bootstrap.DubboBootstrap.start(DubboBootstrap.java:744) ~[dubbo-2.7.7.jar:2.7.7]at org.apache.dubbo.config.spring.context.DubboBootstrapApplicationListener.onContextRefreshedEvent(DubboBootstrapApplicationListener.java:59) ~[dubbo-2.7.7.jar:2.7.7]at org.apache.dubbo.config.spring.context.DubboBootstrapApplicationListener.onApplicationContextEvent(DubboBootstrapApplicationListener.java:52) ~[dubbo-2.7.7.jar:2.7.7]at org.apache.dubbo.config.spring.context.OneTimeExecutionApplicationContextEventListener.onApplicationEvent(OneTimeExecutionApplicationContextEventListener.java:40) ~[dubbo-2.7.7.jar:2.7.7]at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172) ~[spring-context-5.2.7.RELEASE.jar:5.2.7.RELEASE]at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165) ~[spring-context-5.2.7.RELEASE.jar:5.2.7.RELEASE]at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139) ~[spring-context-5.2.7.RELEASE.jar:5.2.7.RELEASE]at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:404) ~[spring-context-5.2.7.RELEASE.jar:5.2.7.RELEASE]at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:361) ~[spring-context-5.2.7.RELEASE.jar:5.2.7.RELEASE]at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:898) ~[spring-context-5.2.7.RELEASE.jar:5.2.7.RELEASE]at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:554) ~[spring-context-5.2.7.RELEASE.jar:5.2.7.RELEASE]at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:143) ~[spring-boot-2.3.1.RELEASE.jar:2.3.1.RELEASE]at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:758) [spring-boot-2.3.1.RELEASE.jar:2.3.1.RELEASE]at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:750) [spring-boot-2.3.1.RELEASE.jar:2.3.1.RELEASE]at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) [spring-boot-2.3.1.RELEASE.jar:2.3.1.RELEASE]at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) [spring-boot-2.3.1.RELEASE.jar:2.3.1.RELEASE]at org.springframework.boot.SpringApplication.run(SpringApplication.java:1237) [spring-boot-2.3.1.RELEASE.jar:2.3.1.RELEASE]at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) [spring-boot-2.3.1.RELEASE.jar:2.3.1.RELEASE]at com.tom.bootdubboorderprovider.BootDubboOrderProviderApplication.main(BootDubboOrderProviderApplication.java:12) [classes/:na]
Caused by: java.lang.IllegalStateException: zookeeper not connectedat org.apache.dubbo.remoting.zookeeper.curator.CuratorZookeeperClient.<init>(CuratorZookeeperClient.java:80) ~[dubbo-2.7.7.jar:2.7.7]... 30 common frames omitted2020-06-29 23:20:58.928 INFO 5200 --- [ main] .b.c.e.AwaitingNonWebApplicationListener : [Dubbo] Current Spring Boot Application is about to shutdown...
2020-06-29 23:20:58.935 INFO 5200 --- [ main] o.s.s.concurrent.ThreadPoolTaskExecutor : Shutting down ExecutorService 'applicationTaskExecutor'
2020-06-29 23:20:58.935 INFO 5200 --- [ main] f.a.ReferenceAnnotationBeanPostProcessor : class org.apache.dubbo.config.spring.beans.factory.annotation.ReferenceAnnotationBeanPostProcessor was destroying!Process finished with exit code 1
点开报错信息，跟踪进源码，发现异常的抛出是由于在等待连接返回时的返回值false
跟进方法，可以看到他在不断循环等待连接成功，若在最大等待时间内连接上，则返回true，否则false
综合所述，猜测是由于网络原因，超时所致（毕竟穷逼买的是100多块钱一年的服务器~~~）
二、继续深入
猜出了大概原因，如果是超时所致，且使用 dubbo-admin 发现 Zookeeper 运行状态正常，那么只要提高最大等待时间就可以了
根据关键字发现，可能跟 metadata-report 的设置有关，且 timeout 有个默认值 5 秒
继续跟踪，查找 CuratorZookeeperClient 方法的调用
结果很明显，这个 timeout 是从配置文件中读取出来的，若没有，则是 5000 ms
三、修改配置文件
# 设置最大等待时间为10秒
dubbo.metadata-report.timeout=10000
四、重试 => 翻车
重试依旧报错，查看
再去找配置文件
# 配置中心连接时间改为10秒
dubbo.config-center.timeout=10000
