Spring Cloud学习笔记【四】断路器Hystrix

雪崩效应

在微服务架构中通常会有多个服务层调用，基础服务的故障可能会导致级联故障，进而造成整个系统不可用的情况，这种现象被称为服务雪崩效应。服务雪崩效应是一种因 “服务提供者” 的不可用导致 “服务消费者” 的不可用, 并将不可用逐渐放大的过程。
如果下图所示：A 作为服务提供者，B 为 A 的服务消费者，C 和 D 是 B 的服务消费者。A 不可用引起了 B 的不可用，并将不可用像滚雪球一样放大到 C 和 D 时，雪崩效应就形成了。

断路器

Netflix 创建了一个名为 Hystrix 的库, 实现了断路器的模式。“断路器” 本身是一种开关装置，当某个服务单元发生故障之后，通过断路器的故障监控（类似熔断保险丝），向调用方返回一个符合预期的、可处理的备选响应（FallBack），而不是长时间的等待或者抛出调用方无法处理的异常，这样就保证了服务调用方的线程不会被长时间、不必要地占用，从而避免了故障在分布式系统中的蔓延，乃至雪崩。

当然，在请求失败频率较低的情况下，Hystrix 还是会直接把故障返回给客户端。只有当失败次数达到阈值时，断路器打开并且不进行后续通信，而是直接返回备选响应。当然，Hystrix 的备选响应也是可以由开发者定制的。

Ribbon 整合 Hystrix

新建spring start project，导入依赖

 <dependencies>

    <dependency>

        <groupId>org.springframework.boot</groupId>

        <artifactId>spring-boot-starter-web</artifactId>

    </dependency>

    <dependency>

        <groupId>org.springframework.cloud</groupId>

        <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>

    </dependency>

    <dependency>

        <groupId>org.springframework.cloud</groupId>

        <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>

    </dependency>

    <dependency>

        <groupId>org.springframework.cloud</groupId>

        <artifactId>spring-cloud-starter-netflix-ribbon</artifactId>

    </dependency>

</dependencies>

属性配置（application.yml）

server:

  port: 9001

spring:

  application:

    name: service-hystrix-ribbon

eureka:

  client:

    serviceUrl:

      defaultZone: http://admin:123456@localhost:8761/eureka/

开启hystrix功能，在启动类上加上@EnableHystrix注解

 package com.carry.springcloud;

 import org.springframework.boot.SpringApplication;

 import org.springframework.boot.autoconfigure.SpringBootApplication;

 import org.springframework.cloud.client.loadbalancer.LoadBalanced;

 import org.springframework.cloud.netflix.eureka.EnableEurekaClient;

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

 import org.springframework.context.annotation.Bean;

 import org.springframework.web.client.RestTemplate;

 @EnableHystrix

 @EnableEurekaClient

 @SpringBootApplication

 public class ServiceHystrixRibbonApplication {

     public static void main(String[] args) {

         SpringApplication.run(ServiceHystrixRibbonApplication.class, args);

     }

     @Bean

     @LoadBalanced

     RestTemplate restTemplate() {

         return new RestTemplate();

     }

 }

添加fallback方法

package com.carry.springcloud.controller;

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

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

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

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

import org.springframework.web.client.RestTemplate;

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

@RestController

public class RibbonController {

    @Autowired

    RestTemplate restTemplate;

    @Value("${server.port}")

    String port;

    @GetMapping("/getPoducerInfo")

    @HystrixCommand(fallbackMethod = "getPoducerInfoFallback")

    public String getPoducerInfo() {

        String result = this.restTemplate.getForObject("http://service-producer/getPortInfo", String.class);

        return result;

    }

    public String getPoducerInfoFallback(){

        return "getPoducerInfo异常，端口：" + port;

    }

}

测试

依次启动eureka-server、service-producer、service-hystrix-ribbon，如下图成功注册到eureka

访问localhost:9001/getPoducerInfo，结果轮询显示8080与8081，停掉8081

接着访问localhost:9001/getPoducerInfo，当访问到8081时出现以下结果，说明服务降级调用了fallback方法

Feign 整合 Hystrix

新建项目并导入依赖

 <dependencies>

    <dependency>

        <groupId>org.springframework.boot</groupId>

        <artifactId>spring-boot-starter-web</artifactId>

    </dependency>

    <dependency>

        <groupId>org.springframework.cloud</groupId>

        <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>

    </dependency>

    <dependency>

        <groupId>org.springframework.cloud</groupId>

        <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>

    </dependency>

    <dependency>

        <groupId>org.springframework.cloud</groupId>

        <artifactId>spring-cloud-starter-openfeign</artifactId>

    </dependency>

</dependencies>

配置属性

server:

  port: 9002

spring:

  application:

    name: service-hystrix-feign

eureka:

  client:

    serviceUrl:

      defaultZone: http://admin:123456@localhost:8761/eureka/

feign:

  hystrix:

    enabled: true

启动类开启Feign支持

 package com.carry.springcloud;

 import org.springframework.boot.SpringApplication;

 import org.springframework.boot.autoconfigure.SpringBootApplication;

 import org.springframework.cloud.openfeign.EnableFeignClients;

 @EnableFeignClients

 @SpringBootApplication

 public class ServiceHystrixFeignApplication {

     public static void main(String[] args) {

         SpringApplication.run(ServiceHystrixFeignApplication.class, args);

     }

 }

添加Feign接口

 package com.carry.springcloud.api;

 import org.springframework.cloud.openfeign.FeignClient;

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

 import com.carry.springcloud.fallback.ConsumerFeignFallback;

 @FeignClient(name = "service-producer", fallback = ConsumerFeignFallback.class)

 public interface ConsumerFeignClient {

     @GetMapping("/getPortInfo")

     public String produce();

 }

添加fallback类

 package com.carry.springcloud.fallback;

 import org.springframework.stereotype.Component;

 import com.carry.springcloud.api.ConsumerFeignClient;

 @Component

 public class ConsumerFeignFallback implements ConsumerFeignClient {

     @Override

     public String produce() {

         return "服务调用失败！";

     }

 }

控制层注入Feign接口

 package com.carry.springcloud.controller;

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

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

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

 import com.carry.springcloud.api.ConsumerFeignClient;

 @RestController

 public class ConsumerController {

     @Autowired

     private ConsumerFeignClient feignClient;

     @GetMapping("/getPoducerInfoByFeign")

     public String getPoducerInfoByFeign() {

         return feignClient.produce();

     }

 }

测试

测试方法同上不再赘述