Spring Cloud构建微服务架构（三）断路器

迈不过友情╰ 2022-07-15 11:55 175阅读 0赞

# 在微服务架构中，我们将系统拆分成了一个个的服务单元，各单元间通过服务注册与订阅的方式互相依赖。由于每个单元都在不同的进程中运行，依赖通过远程调用的方式执行，这样就有可能因为网络原因或是依赖服务自身问题出现调用故障或延迟，而这些问题会直接导致调用方的对外服务也出现延迟，若此时调用方的请求不断增加，最后就会出现因等待出现故障的依赖方响应而形成任务积压，最终导致自身服务的瘫痪。 #

举个例子，在一个电商网站中，我们可能会将系统拆分成，用户、订单、库存、积分、评论等一系列的服务单元。用户创建一个订单的时候，在调用订单服务创建订单的时候，会向库存服务来请求出货（判断是否有足够库存来出货）。此时若库存服务因网络原因无法被访问到，导致创建订单服务的线程进入等待库存申请服务的响应，在漫长的等待之后用户会因为请求库存失败而得到创建订单失败的结果。如果在高并发情况之下，因这些等待线程在等待库存服务的响应而未能释放，使得后续到来的创建订单请求被阻塞，最终导致订单服务也不可用。

在微服务架构中，存在着那么多的服务单元，若一个单元出现故障，就会因依赖关系形成故障蔓延，最终导致整个系统的瘫痪，这样的架构相较传统架构就更加的不稳定。为了解决这样的问题，因此产生了断路器模式。

## 什么是断路器 ##

断路器模式源于Martin Fowler的[Circuit Breaker][]一文。“断路器”本身是一种开关装置，用于在电路上保护线路过载，当线路中有电器发生短路时，“断路器”能够及时的切断故障电路，防止发生过载、发热、甚至起火等严重后果。

在分布式架构中，断路器模式的作用也是类似的，当某个服务单元发生故障（类似用电器发生短路）之后，通过断路器的故障监控（类似熔断保险丝），向调用方返回一个错误响应，而不是长时间的等待。这样就不会使得线程因调用故障服务被长时间占用不释放，避免了故障在分布式系统中的蔓延。

## Netflix Hystrix ##

在Spring Cloud中使用了[Hystrix][] 来实现断路器的功能。Hystrix是Netflix开源的微服务框架套件之一，该框架目标在于通过控制那些访问远程系统、服务和第三方库的节点，从而对延迟和故障提供更强大的容错能力。Hystrix具备拥有回退机制和断路器功能的线程和信号隔离，请求缓存和请求打包，以及监控和配置等功能。

下面我们来看看如何使用Hystrix。

#### 准备工作 ####

在开始加入断路器之前，我们先拿之前构建两个微服务为基础进行下面的操作，主要使用下面几个工程：

*  [chapter9-1-1][]
    
     *  eureka-server工程：服务注册中心，端口1111
     *  compute-service工程：服务单元，端口2222
 *  [chapter9-1-2][]
    
     *  eureka-ribbon：通过ribbon实现的服务单元，依赖compute-service的服务，端口3333
     *  eureka-feign：通过feign实现的服务单元，依赖compute-service的服务，端口3333

若您还没有使用Spring Cloud的经验，可以先阅读[《服务注册与发现》][Link 1]与[《服务消费者》][Link 2]，对Spring Cloud构建的微服务有一个初步的认识。

#### Ribbon中引入Hystrix ####

*  依次启动eureka-server、compute-service、eureka-ribbon工程
 *  访问[http://localhost:1111/][http_localhost_1111]可以看到注册中心的状态
 *  访问[http://localhost:3333/add][http_localhost_3333_add]，调用eureka-ribbon的服务，该服务会去调用compute-service的服务，计算出10+20的值，页面显示30
 *  关闭compute-service服务，访问[http://localhost:3333/add][http_localhost_3333_add]，我们获得了下面的报错信息

*  `pom.xml`中引入依赖hystrix依赖

*  在eureka-ribbon的主类`RibbonApplication`中使用`@EnableCircuitBreaker`注解开启断路器功能：

<table style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; font-size:16px; vertical-align:middle; border-collapse:collapse; border-spacing:0px; line-height:1.6em; width:auto"> 
 <tbody style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"> 
  <tr style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"> 
   <td style="margin:0px; padding:10px 0px; border:none; outline:0px; font-style:inherit; font-family:inherit; font-size:16px; vertical-align:middle"> <pre style="margin-top:0px; margin-bottom:0px; padding:0px 20px 0px 0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(102,102,102); text-align:right">
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       1
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       2
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       3
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       4
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       5
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       6
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       7
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       8
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       9
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       10
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       11
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       12
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       13
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       14
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       15
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       16
      
       
     </div></pre> </td> 
   <td style="margin:0px; padding:10px 20px 10px 0px; border:none; outline:0px; font-style:inherit; font-family:inherit; font-size:16px; vertical-align:middle"> <pre style="margin-top:0px; margin-bottom:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline">
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(117,113,94)">@SpringBootApplication</span>
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(117,113,94)">@EnableDiscoveryClient</span>
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(117,113,94)">@EnableCircuitBreaker</span>
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">public</span> 
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">class</span> <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(255,255,255)">RibbonApplication</span> </span>{
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em"></div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">	
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(117,113,94)">@Bean</span>
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">	
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(117,113,94)">@LoadBalanced</span>
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">	
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline">RestTemplate <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(166,226,46)">restTemplate</span><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline">()</span> </span>{
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">		
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">return</span> 
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">new</span> RestTemplate();
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       	}
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em"></div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">	
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">public</span> <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">static</span> <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">void</span> <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(166,226,46)">main</span><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline">(String[] args)</span> </span>{
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       		SpringApplication.run(RibbonApplication.class, args);
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       	}
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em"></div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       }
      
       
     </div></pre> </td> 
  </tr> 
 </tbody> 
</table>

*  改造原来的服务消费方式，新增`ComputeService`类，在使用ribbon消费服务的函数上增加`@HystrixCommand`注解来指定回调方法。

<table style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; font-size:16px; vertical-align:middle; border-collapse:collapse; border-spacing:0px; line-height:1.6em; width:auto"> 
 <tbody style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"> 
  <tr style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"> 
   <td style="margin:0px; padding:10px 0px; border:none; outline:0px; font-style:inherit; font-family:inherit; font-size:16px; vertical-align:middle"> <pre style="margin-top:0px; margin-bottom:0px; padding:0px 20px 0px 0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(102,102,102); text-align:right">
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       1
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       2
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       3
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       4
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       5
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       6
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       7
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       8
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       9
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       10
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       11
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       12
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       13
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       14
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       15
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       16
      
       
     </div></pre> </td> 
   <td style="margin:0px; padding:10px 20px 10px 0px; border:none; outline:0px; font-style:inherit; font-family:inherit; font-size:16px; vertical-align:middle"> <pre style="margin-top:0px; margin-bottom:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline">
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(117,113,94)">@Service</span>
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">public</span> 
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">class</span> <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(255,255,255)">ComputeService</span> </span>{
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em"></div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">    
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(117,113,94)">@Autowired</span>
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
           RestTemplate restTemplate;
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em"></div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">    
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(117,113,94)">@HystrixCommand</span>(fallbackMethod = 
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(166,226,46)">"addServiceFallback"</span>)
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">    
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">public</span> String <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(166,226,46)">addService</span><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline">()</span> </span>{
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">        
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">return</span> restTemplate.getForEntity(
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(166,226,46)">"http://COMPUTE-SERVICE/add?a=10&amp;b=20"</span>, String.class).getBody();
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
           }
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em"></div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">    
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">public</span> String <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(166,226,46)">addServiceFallback</span><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline">()</span> </span>{
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">        
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">return</span> 
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(166,226,46)">"error"</span>;
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
           }
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em"></div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       }
      
       
     </div></pre> </td> 
  </tr> 
 </tbody> 
</table>

*  提供rest接口的Controller改为调用ComputeService的addService

<table style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; font-size:16px; vertical-align:middle; border-collapse:collapse; border-spacing:0px; line-height:1.6em; width:auto"> 
 <tbody style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"> 
  <tr style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"> 
   <td style="margin:0px; padding:10px 0px; border:none; outline:0px; font-style:inherit; font-family:inherit; font-size:16px; vertical-align:middle"> <pre style="margin-top:0px; margin-bottom:0px; padding:0px 20px 0px 0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(102,102,102); text-align:right">
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       1
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       2
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       3
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       4
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       5
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       6
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       7
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       8
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       9
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       10
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       11
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       12
      
       
     </div></pre> </td> 
   <td style="margin:0px; padding:10px 20px 10px 0px; border:none; outline:0px; font-style:inherit; font-family:inherit; font-size:16px; vertical-align:middle"> <pre style="margin-top:0px; margin-bottom:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline">
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(117,113,94)">@RestController</span>
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">public</span> 
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">class</span> <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(255,255,255)">ConsumerController</span> </span>{
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em"></div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">    
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(117,113,94)">@Autowired</span>
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">    
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">private</span> ComputeService computeService;
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em"></div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">    
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(117,113,94)">@RequestMapping</span>(value = 
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(166,226,46)">"/add"</span>, method = RequestMethod.GET)
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">    
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">public</span> String <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(166,226,46)">add</span><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline">()</span> </span>{
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">        
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">return</span> computeService.addService();
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
           }
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em"></div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       }
      
       
     </div></pre> </td> 
  </tr> 
 </tbody> 
</table>

*  验证断路器的回调
    
     *  依次启动eureka-server、compute-service、eureka-ribbon工程
     *  访问[http://localhost:1111/][http_localhost_1111]可以看到注册中心的状态
     *  访问[http://localhost:3333/add][http_localhost_3333_add]，页面显示：30
     *  关闭compute-service服务后再访问[http://localhost:3333/add][http_localhost_3333_add]，页面显示：error

更多关于Hystrix的使用可参考[How To Use][]

#### Feign使用Hystrix ####

注意这里说的是“使用”，没有错，我们不需要在Feigh工程中引入Hystix，Feign中已经依赖了Hystrix，我们可以在未做任何改造前，尝试下面你的操作：

*  依次启动eureka-server、compute-service、eureka-feign工程
 *  访问[http://localhost:1111/][http_localhost_1111]可以看到注册中心的状态
 *  访问[http://localhost:3333/add][http_localhost_3333_add]，调用eureka-feign的服务，该服务会去调用compute-service的服务，计算出10+20的值，页面显示30
 *  关闭compute-service服务，访问[http://localhost:3333/add][http_localhost_3333_add]，我们获得了下面的报错信息

如果您够仔细，会发现与在ribbon中的报错是不同的，看到`add timed-out and no fallback available`这句，或许您已经猜到什么，看看我们的控制台，可以看到报错信息来自`hystrix-core-1.5.2.jar`，所以在这个工程中，我们要学习的就是如何使用Feign中集成的Hystrix。

*  使用`@FeignClient`注解中的fallback属性指定回调类

*  创建回调类`ComputeClientHystrix`，实现`@FeignClient`的接口，此时实现的方法就是对应`@FeignClient`接口中映射的fallback函数。

<table style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; font-size:16px; vertical-align:middle; border-collapse:collapse; border-spacing:0px; line-height:1.6em; width:auto"> 
 <tbody style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"> 
  <tr style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"> 
   <td style="margin:0px; padding:10px 0px; border:none; outline:0px; font-style:inherit; font-family:inherit; font-size:16px; vertical-align:middle"> <pre style="margin-top:0px; margin-bottom:0px; padding:0px 20px 0px 0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(102,102,102); text-align:right">
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       1
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       2
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       3
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       4
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       5
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       6
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       7
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       8
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       9
      
       
     </div></pre> </td> 
   <td style="margin:0px; padding:10px 20px 10px 0px; border:none; outline:0px; font-style:inherit; font-family:inherit; font-size:16px; vertical-align:middle"> <pre style="margin-top:0px; margin-bottom:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline">
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(117,113,94)">@Component</span>
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">public</span> 
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">class</span> <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(255,255,255)">ComputeClientHystrix</span> <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">implements</span> <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(255,255,255)">ComputeClient</span> </span>{
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em"></div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">    
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(117,113,94)">@Override</span>
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">    
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline"><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">public</span> Integer <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(166,226,46)">add</span><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline">(@RequestParam(value = <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(166,226,46)">"a"</span>)</span> Integer a, @<span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(166,226,46)">RequestParam</span><span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline">(value = <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(166,226,46)">"b"</span>)</span> Integer b) </span>{
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">        
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:bold; font-style:inherit; font-family:inherit; vertical-align:baseline; color:rgb(249,38,114)">return</span> -
       
        
      <span style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline">9999</span>;
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
           }
      
       
     </div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em"></div>
      
       
     <div style="margin:0px; padding:0px; border:0px; outline:0px; font-weight:inherit; font-style:inherit; font-family:inherit; vertical-align:baseline; height:1.6em">
      
        
       }
      
       
     </div></pre> </td> 
  </tr> 
 </tbody> 
</table>

*  再用之前的方法验证一下，是否在compute-service服务不可用的情况下，页面返回了-9999。

关于Feign的更多使用方法可参考：[Feign][]

完整示例：[Chapter9-1-3][]

【转载请注明出处】：[http://blog.didispace.com/springcloud3/][http_blog.didispace.com_springcloud3]

[Circuit Breaker]: http://martinfowler.com/bliki/CircuitBreaker.html
[Hystrix]: https://github.com/Netflix/Hystrix
[chapter9-1-1]: http://git.oschina.net/didispace/SpringBoot-Learning/tree/master/Chapter9-1-1
[chapter9-1-2]: http://git.oschina.net/didispace/SpringBoot-Learning/tree/master/Chapter9-1-2
[Link 1]: http://blog.didispace.com/springcloud1/
[Link 2]: http://blog.didispace.com/springcloud2/
[http_localhost_1111]: http://localhost:1111/
[http_localhost_3333_add]: http://localhost:3333/add
[How To Use]: https://github.com/Netflix/Hystrix/wiki/How-To-Use
[Feign]: https://github.com/Netflix/feign
[Chapter9-1-3]: http://git.oschina.net/didispace/SpringBoot-Learning/tree/master/Chapter9-1-3
[http_blog.didispace.com_springcloud3]: http://blog.didispace.com/springcloud3/