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