前言
apollo是一个非常流行的开源的配置中心项目，这里就不多介绍了。接触过apollo和运行过apollo的人肯定都遇到过启动configService时抛异常了，而且100%会抛一个异常。原因是，在apollo的架构中configService既作为config服务，同时也承载了metaService的功能，所以这个模块，既作为eureka的服务端也是eureka的客户端，这就造成了应用启动时，eurekaServer未完全启动，eurekaClient拉取注册表信息时就抛异常了。不过这个拉取动作是在独立的线程中运行的，独立于启动应用的主线程，所以异常并不影响应用的启动，这个问题也就一直从开源到留到了现在。目前，这个问题已被博主解决，正在合并pr中。
本文pr地址：https://github.com/ctripcorp/apollo/pull/3450
触发原因分析
首先看下异常的信息，异常的信息比较多，如下：
2020-12-23 09:55:19.882 ERROR 7022 --- [ main] c.n.d.s.t.d.RedirectingEurekaHttpClient : Request execution error
com.sun.jersey.api.client.ClientHandlerException: java.net.ConnectException: Connection refused (Connection refused)
at com.sun.jersey.client.apache4.ApacheHttpClient4Handler.handle(ApacheHttpClient4Handler.java:187)
at com.sun.jersey.api.client.filter.GZIPContentEncodingFilter.handle(GZIPContentEncodingFilter.java:123)
at com.netflix.discovery.EurekaIdentityHeaderFilter.handle(EurekaIdentityHeaderFilter.java:27)
at com.sun.jersey.api.client.Client.handle(Client.java:652)
at com.sun.jersey.api.client.WebResource.handle(WebResource.java:682)
at com.sun.jersey.api.client.WebResource.access$200(WebResource.java:74)
at com.sun.jersey.api.client.WebResource$Builder.get(WebResource.java:509)
at com.netflix.discovery.shared.transport.jersey.AbstractJerseyEurekaHttpClient.getApplicationsInternal(AbstractJerseyEurekaHttpClient.java:194)
at com.netflix.discovery.shared.transport.jersey.AbstractJerseyEurekaHttpClient.getApplications(AbstractJerseyEurekaHttpClient.java:165)
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$6.execute(EurekaHttpClientDecorator.java:137)
at com.netflix.discovery.shared.transport.decorator.MetricsCollectingEurekaHttpClient.execute(MetricsCollectingEurekaHttpClient.java:73)
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.getApplications(EurekaHttpClientDecorator.java:134)
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$6.execute(EurekaHttpClientDecorator.java:137)
at com.netflix.discovery.shared.transport.decorator.RedirectingEurekaHttpClient.executeOnNewServer(RedirectingEurekaHttpClient.java:118)
at com.netflix.discovery.shared.transport.decorator.RedirectingEurekaHttpClient.execute(RedirectingEurekaHttpClient.java:79)
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.getApplications(EurekaHttpClientDecorator.java:134)
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$6.execute(EurekaHttpClientDecorator.java:137)
at com.netflix.discovery.shared.transport.decorator.RetryableEurekaHttpClient.execute(RetryableEurekaHttpClient.java:120)
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.getApplications(EurekaHttpClientDecorator.java:134)
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$6.execute(EurekaHttpClientDecorator.java:137)
at com.netflix.discovery.shared.transport.decorator.SessionedEurekaHttpClient.execute(SessionedEurekaHttpClient.java:77)
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.getApplications(EurekaHttpClientDecorator.java:134)
at com.netflix.discovery.DiscoveryClient.getAndStoreFullRegistry(DiscoveryClient.java:1051)
at com.netflix.discovery.DiscoveryClient.fetchRegistry(DiscoveryClient.java:965)
at com.netflix.discovery.DiscoveryClient.<init>(DiscoveryClient.java:414)
at com.netflix.discovery.DiscoveryClient.<init>(DiscoveryClient.java:269)
at org.springframework.cloud.netflix.eureka.CloudEurekaClient.<init>(CloudEurekaClient.java:63)
at org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration$RefreshableEurekaClientConfiguration.eurekaClient(EurekaClientAutoConfiguration.java:290)
at org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration$RefreshableEurekaClientConfiguration$$EnhancerBySpringCGLIB$$5cf7ced9.CGLIB$eurekaClient$2(<generated>)
at org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration$RefreshableEurekaClientConfiguration$$EnhancerBySpringCGLIB$$5cf7ced9$$FastClassBySpringCGLIB$$328872d8.invoke(<generated>)
at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228)
at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:365)
at org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration$RefreshableEurekaClientConfiguration$$EnhancerBySpringCGLIB$$5cf7ced9.eurekaClient(<generated>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154)
at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:582)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1247)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1096)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:535)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$1(AbstractBeanFactory.java:353)
at org.springframework.cloud.context.scope.GenericScope$BeanLifecycleWrapper.getBean(GenericScope.java:390)
at org.springframework.cloud.context.scope.GenericScope.get(GenericScope.java:184)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:350)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
at org.springframework.aop.target.SimpleBeanTargetSource.getTarget(SimpleBeanTargetSource.java:35)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:193)
at com.sun.proxy.$Proxy145.getApplications(Unknown Source)
at org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration.peerAwareInstanceRegistry(EurekaServerAutoConfiguration.java:164)
at org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration$$EnhancerBySpringCGLIB$$ef07d99b.CGLIB$peerAwareInstanceRegistry$5(<generated>)
at org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration$$EnhancerBySpringCGLIB$$ef07d99b$$FastClassBySpringCGLIB$$458f0ac6.invoke(<generated>)
at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228)
at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:365)
at org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration$$EnhancerBySpringCGLIB$$ef07d99b.peerAwareInstanceRegistry(<generated>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154)
at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:582)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1247)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1096)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:535)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:251)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1135)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1062)
at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:818)
at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:724)
at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:474)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1247)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1096)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:535)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:251)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1135)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1062)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:583)
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:90)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:372)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1341)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:572)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:759)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:869)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:780)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:412)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:333)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1277)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1265)
at com.ctrip.framework.apollo.configservice.ConfigServiceApplication.main(ConfigServiceApplication.java:33)
Caused by: java.net.ConnectException: Connection refused (Connection refused)
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:476)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:218)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:200)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:394)
at java.net.Socket.connect(Socket.java:606)
at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:121)
at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:180)
at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:144)
at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:134)
at org.apache.http.impl.client.DefaultRequestDirector.tryConnect(DefaultRequestDirector.java:610)
at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:445)
at org.apache.http.impl.client.AbstractHttpClient.doExecute(AbstractHttpClient.java:835)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:118)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:56)
at com.sun.jersey.client.apache4.ApacheHttpClient4Handler.handle(ApacheHttpClient4Handler.java:173)
... 107 common frames omitted
2020-12-23 09:55:19.883 WARN 7022 --- [ main] c.n.d.s.t.d.RetryableEurekaHttpClient : Request execution failed with message: java.net.ConnectException: Connection refused (Connection refused)
2020-12-23 09:55:19.883 ERROR 7022 --- [ main] com.netflix.discovery.DiscoveryClient : DiscoveryClient_APOLLO-CONFIGSERVICE/172.26.203.178:apollo-configservice:8080 - was unable to refresh its cache! status = Cannot execute request on any known server
com.netflix.discovery.shared.transport.TransportException: Cannot execute request on any known server
at com.netflix.discovery.shared.transport.decorator.RetryableEurekaHttpClient.execute(RetryableEurekaHttpClient.java:112)
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.getApplications(EurekaHttpClientDecorator.java:134)
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$6.execute(EurekaHttpClientDecorator.java:137)
at com.netflix.discovery.shared.transport.decorator.SessionedEurekaHttpClient.execute(SessionedEurekaHttpClient.java:77)
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.getApplications(EurekaHttpClientDecorator.java:134)
at com.netflix.discovery.DiscoveryClient.getAndStoreFullRegistry(DiscoveryClient.java:1051)
at com.netflix.discovery.DiscoveryClient.fetchRegistry(DiscoveryClient.java:965)
at com.netflix.discovery.DiscoveryClient.<init>(DiscoveryClient.java:414)
at com.netflix.discovery.DiscoveryClient.<init>(DiscoveryClient.java:269)
at org.springframework.cloud.netflix.eureka.CloudEurekaClient.<init>(CloudEurekaClient.java:63)
at org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration$RefreshableEurekaClientConfiguration.eurekaClient(EurekaClientAutoConfiguration.java:290)
at org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration$RefreshableEurekaClientConfiguration$$EnhancerBySpringCGLIB$$5cf7ced9.CGLIB$eurekaClient$2(<generated>)
at org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration$RefreshableEurekaClientConfiguration$$EnhancerBySpringCGLIB$$5cf7ced9$$FastClassBySpringCGLIB$$328872d8.invoke(<generated>)
at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228)
at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:365)
at org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration$RefreshableEurekaClientConfiguration$$EnhancerBySpringCGLIB$$5cf7ced9.eurekaClient(<generated>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154)
at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:582)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1247)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1096)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:535)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$1(AbstractBeanFactory.java:353)
at org.springframework.cloud.context.scope.GenericScope$BeanLifecycleWrapper.getBean(GenericScope.java:390)
at org.springframework.cloud.context.scope.GenericScope.get(GenericScope.java:184)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:350)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
at org.springframework.aop.target.SimpleBeanTargetSource.getTarget(SimpleBeanTargetSource.java:35)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:193)
at com.sun.proxy.$Proxy145.getApplications(Unknown Source)
at org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration.peerAwareInstanceRegistry(EurekaServerAutoConfiguration.java:164)
at org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration$$EnhancerBySpringCGLIB$$ef07d99b.CGLIB$peerAwareInstanceRegistry$5(<generated>)
at org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration$$EnhancerBySpringCGLIB$$ef07d99b$$FastClassBySpringCGLIB$$458f0ac6.invoke(<generated>)
at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228)
at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:365)
at org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration$$EnhancerBySpringCGLIB$$ef07d99b.peerAwareInstanceRegistry(<generated>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154)
at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:582)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1247)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1096)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:535)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:251)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1135)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1062)
at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:818)
at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:724)
at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:474)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1247)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1096)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:535)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:251)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1135)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1062)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:583)
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:90)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:372)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1341)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:572)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:759)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:869)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:780)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:412)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:333)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1277)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1265)
at com.ctrip.framework.apollo.configservice.ConfigServiceApplication.main(ConfigServiceApplication.java:33)
最终我们就定位到这一行，定位问题的过程是一个非常复杂的事情。所以这里直接写明，并不是一开始我就知道关键点在这里，这个需要平时多积累知识面，才能快速定位关键点
at com.netflix.discovery.DiscoveryClient.<init>(DiscoveryClient.java:414)。
代码逻辑如下：
if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
fetchRegistryFromBackup();
}
上面的异常就是这个地方触发的，在初始化eurekaClient时，会通过判断fetchRegistry来触发拉取eurekaServer端的注册表信息，但是这个时候eurekaServer还没准备好，所以抛了如上的异常。fetchRegistry对应了Spring 初始化eurekaClient的一个配置，如：
//是否拉取注册表信息，如果配置为false，则代表只注册，通过eurekaClient获取不到任何实例
eureka.client.fetch-registry=trueeurekaClient的构造
了解了异常触发的原因和触发的节点后，在来详细了解下eurekaClient在spring下是如何被加载的。直接定位到EurekaClientAutoConfiguration.java文件，找到如下的代码：
@Bean(destroyMethod = "shutdown")
@ConditionalOnMissingBean(value = EurekaClient.class, search = SearchStrategy.CURRENT)
@org.springframework.cloud.context.config.annotation.RefreshScope
@Lazy
public EurekaClient eurekaClient(ApplicationInfoManager manager, EurekaClientConfig config, EurekaInstanceConfig instance) {
manager.getInfo(); // force initialization
return new CloudEurekaClient(manager, config, this.optionalArgs,
this.context);
}可以看到EurekaClientConfig是从上下文中注入到这个方法的，而且这个方法贴上了@RefreshScope的标记，代表这个实例可以被动态的刷新，有了这两个特性，我们的解决方案就基本出炉了。通过程序动态控制eurekaClient的fetchRegistry加载时机也就变得可行了。
实施解决方案
最终的解决方案分成了两个关键步骤，如下：
- 1、configService启动前，设置fetchRegistry为false。
- 2、监听EurekaClient的注册事件，判断是否注册成功，注册成功则重新设置fetchRegistry为true，刷新eurekaClient上下文
针对步骤一，直接修改configService模块的bootstrap.yml配置文件，新增fetchRegistry为true的配置，如：
eureka:
instance:
hostname: ${hostname:localhost}
preferIpAddress: true
status-page-url-path: /info
health-check-url-path: /health
server:
peerEurekaNodesUpdateIntervalMs: 60000
enableSelfPreservation: false
client:
serviceUrl:
# This setting will be overridden by eureka.service.url setting from ApolloConfigDB.ServerConfig or System Property
# see com.ctrip.framework.apollo.biz.eureka.ApolloEurekaClientConfig defaultZone: http://${eureka.instance.hostname}:8080/eureka/
healthcheck:
enabled: true
eurekaServiceUrlPollIntervalSeconds: 60
fetch-registry: true
management:
health:
status:
order: DOWN, OUT_OF_SERVICE, UNKNOWN, UP针对步骤二，新增了一个eurekaClient的配置类，如：
/**
* @author : kl
* After startup, set FetchRegistry to true, refresh eureka client
**/
@Configuration
@ConditionalOnProperty(value = "eureka.client.enabled", havingValue = "true", matchIfMissing = true)
public class ConfigServerEurekaClientConfigure {
private static final String EUREKACLIENT_BEANNAME = "eurekaClient";
private final ApolloEurekaClientConfig eurekaClientConfig;
private final AtomicBoolean isRefresh = new AtomicBoolean(false);
private final RefreshScope refreshScope;
public ConfigServerEurekaClientConfigure(ApolloEurekaClientConfig eurekaClientConfig, RefreshScope refreshScope) {
this.eurekaClientConfig = eurekaClientConfig;
this.refreshScope = refreshScope;
}
@EventListener
public void listenEurekaInstanceRegisteredEvent(EurekaInstanceRegisteredEvent event) {
InstanceInfo.InstanceStatus status = event.getInstanceInfo().getStatus();
if (InstanceInfo.InstanceStatus.UP.equals(status) && !eurekaClientConfig.isFetchRegistry()) {
this.refreshEurekaClient();
}
}
private void refreshEurekaClient() {
if (isRefresh.compareAndSet(false, true)) {
eurekaClientConfig.setFetchRegistry(true);
refreshScope.refresh(EUREKACLIENT_BEANNAME);
}
}
}结语
经过改造后，存在了这么久的异常终于消失了。整个过程还是有一些曲折的，最初曾尝试过，自定义EurekaClient的初始化，妄想try住整个的实例化过程，接住异常自行处理，但是忽略了fetchRegistry的过程是在一个新的线程里了。其次，最初的时候以为将fetchRegistry设置为false就ok了，然后在metaService服务获取configService时候啥也获取不到，才明白了fetchRegistry的真正意图。还尝试过将刷新EurekaClient的逻辑放在ApplicationRunner的run方法内，这个造成了结果时好时坏。最终随着对Eureka的深入，才采用了现在的方案，目前的方案还算完美。最后，希望得到大家的测验反馈，早点合并到主干道，解决这个烦人的问题。
