为了解决这个问题，业界提出了熔断器模型。

Netflix 开源了 Hystrix 组件，实现了熔断器模式，Spring Cloud 对这一组件进行了整合。在微服务架构中，一个请求需要调用多个服务是非常常见的，如下图：

较底层的服务如果出现故障，会导致连锁故障。当对特定的服务的调用的不可用达到一个阀值（Hystrix 是 5 秒 20 次） 熔断器将会被打开。

熔断器打开后，为了避免连锁故障，通过 fallback 方法可以直接返回一个固定值。

Dubbo Provider 中使用熔断器

在 pom.xml 中增加依赖

    org.springframework.cloud

    spring-cloud-starter-netflix-hystrix

    2.0.1.RELEASE

/pre>
h4>在 Application 中增加 @EnableHystrix 注解
/h4>
pre class='language-javascript'>
package com.funtl.hello.dubbo.service.user.provider;



import com.alibaba.dubbo.container.Main;

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

import org.springframework.cloud.netflix.hystrix.EnableHystrix;



@EnableHystrix

@SpringBootApplication

public class HelloDubboServiceUserProviderApplication {

    public static void main(String[] args) {

        SpringApplication.run(HelloDubboServiceUserProviderApplication.class, args);

        Main.main(args);

    }

}
/pre>
h4>在 Service 中增加 @HystrixCommand 注解
/h4>
p>在调用方法上增加 @HystrixCommand 配置，此时调用会经过 Hystrix 代理
/p>
pre class='language-javascript'>
package com.funtl.hello.dubbo.service.user.provider.api.impl;



import com.alibaba.dubbo.config.annotation.Service;

import com.funtl.hello.dubbo.service.user.api.UserService;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixProperty;

import org.springframework.beans.factory.annotation.Value;



@Service(version = "${user.service.version}")

public class UserServiceImpl implements UserService {



    @Value("${dubbo.protocol.port}")

    private String port;



    @HystrixCommand(commandProperties = {

            @HystrixProperty(name = "circuitBreaker.requestVolumeThreshold", value = "10"),

            @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "2000")

    })

    @Override

    public String sayHi() {

//        return "Hello Dubbo, i am from port:" + port;

        throw new RuntimeException("Exception to show hystrix enabled.");

    }

}
/pre>
h4>测试熔断器
/h4>
p>此时我们再次请求服务提供者，浏览器会报 500 异常
/p>
pre class='language-javascript'>
Exception to show hystrix enabled.
/pre>
h3>Dubbo Consumer 中使用熔断器
/h3>
h4>在 pom.xml 中增加依赖
/h4>
pre class='language-javascript'>


    org.springframework.cloud

    spring-cloud-starter-netflix-hystrix

    2.0.1.RELEASE

/code>
code class='prism'>package com.funtl.hello.dubbo.service.user.consumer;


import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

import org.springframework.cloud.netflix.hystrix.EnableHystrix;


@EnableHystrix

@SpringBootApplication

public class HelloDubboServiceUserConsumerApplication {

public static void main(String[] args) {

SpringApplication.run(HelloDubboServiceUserConsumerApplication.class, args);

}

}
/code>
code class='prism'>package com.funtl.hello.dubbo.service.user.consumer.controller;


import com.alibaba.dubbo.config.annotation.Reference;

import com.funtl.hello.dubbo.service.user.api.UserService;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RestController;


@RestController

public class UserController {


@Reference(version = "${user.service.version}")

private UserService userService;


@HystrixCommand(fallbackMethod = "hiError")

@RequestMapping(value = "hi")

public String sayHi() {

return userService.sayHi();

}


public String hiError() {

return "Hystrix fallback";

}

}
/code>
code class='prism'>Hystrix fallback
/code>

至此，Dubbo + Hystrix 配置完成

Hystrix配置参数解析