1、先来一段异常看看：No provider available for the service

16:05:25.755 [localhost-startStop-1] WARN  o.s.w.c.s.XmlWebApplicationContext - Exception encountered during context initialization - cancelling refresh attempt
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'quartz': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.test.rpc.OrgRPC com.xinping.crm.until.taglib.Quartz.orgRPC; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'orgRPC': FactoryBean threw exception on object creation; nested exception is java.lang.IllegalStateException: Failed to check the status of the service com.test.rpc.OrgRPC. No provider available for the service com.test.rpc.OrgRPC from the url zookeeper://zookeeper-ip:2181/com.alibaba.dubbo.registry.RegistryService?anyhost=true&application=TEST_CRMWH_HELPER&check=false&dubbo=2.5.3&generic=false&interface=com.test.rpc.OrgRPC&methods=getOrgListByIdOrParentIdOrUpdateTime,getOrgById&pid=7916&revision=1.0.1-api&side=consumer&timeout=60000&timestamp=1471853122008 to the consumer consumer-ip use dubbo version 2.5.3
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:334) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1202) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:537) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:302) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:298) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:762) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757) ~[spring-context-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480) ~[spring-context-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:403) [spring-web-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:306) [spring-web-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:106) [spring-web-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:5016) [catalina.jar:7.0.61]
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5528) [catalina.jar:7.0.61]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) [catalina.jar:7.0.61]
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1575) [catalina.jar:7.0.61]
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1565) [catalina.jar:7.0.61]
    at java.util.concurrent.FutureTask.run(FutureTask.java:262) [na:1.7.0_79]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [na:1.7.0_79]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [na:1.7.0_79]
    at java.lang.Thread.run(Thread.java:745) [na:1.7.0_79]
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.test.rpc.OrgRPC com.xinping.crm.until.taglib.Quartz.orgRPC; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'orgRPC': FactoryBean threw exception on object creation; nested exception is java.lang.IllegalStateException: Failed to check the status of the service com.test.rpc.OrgRPC. No provider available for the service com.test.rpc.OrgRPC from the url zookeeper://zookeeper-ip:2181/com.alibaba.dubbo.registry.RegistryService?anyhost=true&application=TEST_CRMWH_HELPER&check=false&dubbo=2.5.3&generic=false&interface=com.test.rpc.OrgRPC&methods=getOrgListByIdOrParentIdOrUpdateTime,getOrgById&pid=7916&revision=1.0.1-api&side=consumer&timeout=60000&timestamp=1471853122008 to the consumer consumer-ip use dubbo version 2.5.3
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:558) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:87) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:331) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    ... 22 common frames omitted
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'orgRPC': FactoryBean threw exception on object creation; nested exception is java.lang.IllegalStateException: Failed to check the status of the service com.test.rpc.OrgRPC. No provider available for the service com.test.rpc.OrgRPC from the url zookeeper://zookeeper-ip:2181/com.alibaba.dubbo.registry.RegistryService?anyhost=true&application=TEST_CRMWH_HELPER&check=false&dubbo=2.5.3&generic=false&interface=com.test.rpc.OrgRPC&methods=getOrgListByIdOrParentIdOrUpdateTime,getOrgById&pid=7916&revision=1.0.1-api&side=consumer&timeout=60000&timestamp=1471853122008 to the consumer consumer-ip use dubbo version 2.5.3
    at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:175) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.getObjectFromFactoryBean(FactoryBeanRegistrySupport.java:103) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getObjectForBeanInstance(AbstractBeanFactory.java:1506) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:250) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1127) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1051) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:949) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:530) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    ... 24 common frames omitted
Caused by: java.lang.IllegalStateException: Failed to check the status of the service com.test.rpc.OrgRPC. No provider available for the service com.test.rpc.OrgRPC from the url zookeeper://zookeeper-ip:2181/com.alibaba.dubbo.registry.RegistryService?anyhost=true&application=TEST_CRMWH_HELPER&check=false&dubbo=2.5.3&generic=false&interface=com.test.rpc.OrgRPC&methods=getOrgListByIdOrParentIdOrUpdateTime,getOrgById&pid=7916&revision=1.0.1-api&side=consumer&timeout=60000&timestamp=1471853122008 to the consumer consumer-ip use dubbo version 2.5.3
    at com.alibaba.dubbo.config.ReferenceConfig.createProxy(ReferenceConfig.java:420) ~[dubbo-2.5.3.jar:2.5.3]
    at com.alibaba.dubbo.config.ReferenceConfig.init(ReferenceConfig.java:300) ~[dubbo-2.5.3.jar:2.5.3]
    at com.alibaba.dubbo.config.ReferenceConfig.get(ReferenceConfig.java:138) ~[dubbo-2.5.3.jar:2.5.3]
    at com.alibaba.dubbo.config.spring.ReferenceBean.getObject(ReferenceBean.java:65) ~[dubbo-2.5.3.jar:2.5.3]
    at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:168) ~[spring-beans-4.1.3.RELEASE.jar:4.1.3.RELEASE]
    ... 32 common frames omitted
16:05:25.755 [localhost-startStop-1] ERROR o.s.web.context.ContextLoader - Context initialization failed
八月 22, 2016 4:05:25 下午 org.apache.catalina.core.StandardContext startInternal
严重: Error listenerStart
八月 22, 2016 4:05:25 下午 org.apache.catalina.core.StandardContext startInternal
严重: Context [/crm] startup failed due to previous errors
八月 22, 2016 4:05:25 下午 org.apache.catalina.core.ApplicationContext log
信息: Closing Spring root WebApplicationContext

异常分析：

上面的异常，Caused by的前半部分有的说bean创建失败，有的说属性自动装配失败，但后半部分都比较统一，都是：No provider available for the service ……，服务没有可以使用的提供者，完整意思就是：对于消费者(consumer-ip)而言，在zookeeper注册中心(zookeeper-url)没有可用的提供者(No provider available for the service com.test.rpc.OrgRPC)，消费者访问提供者的时候失败了；

因为消费者没有变，变化的是向注册中心注册的提供者由开发服务器变更为测试服务器，同时由于之前处理过因为【No route to host】引起的异常，所以想到可能是提供者端口不通造成的，然后从消费者服务器telnet 提供者ip 20880端口，果然如此。

解决办法：

将提供者服务器的20880端口开放给消费者服务器ip，重新启动消费者服务器，正常启动。

2、dubbo+zookeeper与提供者provider、消费者consumer之间通信过程

先说一下整个系统框架的基本构造：

• zookeeper作为注册中心，使用单独服务器，占用2181端口

• dubbo-admin作为监控中心，与zookeeper使用相同服务器，tomcat部署占用8080端口

• provider作为提供者，使用单独服务器，tomcat部署占用8080端口，使用dubbo协议开放20880端口

• consumer作为消费者，使用单独服务器，tomcat部署占用8080端口

再看上面的异常，虽然解决了，是不是有人和我一样有一些问题想不通：

• provider服务器端口是8080，为什么telnet测试以及解决方案中开放的端口却是20880？

• 要说dubbo协议开放了20880端口，那8080端口应该也开放啊？

• zookeeper、provider、consumer之间端口开放和屏蔽情况到底是怎么回事？

带着这些问题，进行了相关的验证，最终得出如下结论，先看图，再解释：

1)、用dubbo协议在20880端口暴露服务

在提供者的dubbo配置文件中，一般都配置了<dubbo:protocol name="dubbo" port="20880"/>，表明用dubbo协议在20880端口暴露服务，当然如果你不配置，dubbo默认使用20880端口暴露服务，所有消费者都是通过20880端口进行，对于消费者而言，提供者服务器8080端口是透明的，也就是说提供者服务器端口号可以任意改变，服务也不会有任何影响，消费者无需关心。

所以上面的异常解决办法是开放20880端口给消费者，而不是8080端口给消费者。

从监控中心可以看到如图：

除了在指定端口上暴露服务之外，还可以在指定ip上暴露服务，配置如下：

<dubbo:protocol name="dubbo" host="10.1.22.2" port="20880" />

2)、端口开放情况

zookeeper作为注册中心，provider注册服务、consumer订阅服务、dubbo-admin监控服务，所以zookeeper注册中心的2181端口需要向provider、consumer、dubbo-admin开放；

一般情况下，dubbo-admin监控中心与zookeeper注册中心部署在相同的服务器上，zookeeper可以不考虑端口开放给dubbo-admin的情况；

consumer订阅服务，即拿到了provider在20880端口暴露的服务，当consumer请求服务时，直接从consumer跳到provider，而不是consumer到zookeeper再到provider，所以provider的20880无需开放给zookeeper；

同理，provider响应服务时，也是直接从provider到consumer，而不是provider到zookeeper再到consumer，所以consumer的8080无需开放给zookeeper；

zookeeper注册中心是完全被动的。

总结一下：

- zookeeper的2181开放给provider、consumer、dubbo-admin

- provider的20880开放给所有consumer，但8080服务器端口可以完全屏蔽

- consumer的8080开放给所有provider

- dubbo-admin的8080开放给管理员用户，便于通过浏览器监控注册中心服务的情况

- 总结：注册中心只负责服务注册和目录发布，安全授权，实际的服务访问仍然是两个组件之间的点对点连接完成，这种方式下整个架构下获取更高的性能，同时服务管理平台也不容易成为大并发服务访问下的单点瓶颈