Spring cloud 熔断器 Hystrix 防止服务雪崩

在分布式系统中，一种不可避免的情况就是某些服务会出现故障，导致依赖他们的其他服务出现远程调度的线程问题（雪崩效应）。而Hystrix提供的熔断器，通过隔离服务的访问点，能阻止这种分布式系统中出现的联动故障，并提供故障的解决方案，从而提高了整个分布式系统的弹性。

Ribbon中使用Hystrix(熔断器)

  1.在Ribbon的pom.xml中添加依赖 

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
</dependency>

2.在application中增加注解启动熔断器Hystrix

package com.lxq.hello.spring.cloud.web.admin.ribbon;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.netflix.hystrix.EnableHystrix;

/**
 * @Author Lxq
 * @Date 2020/3/29 13:28
 * @Version 1.0
 */
@EnableHystrix
@SpringBootApplication
@EnableDiscoveryClient
public class WebAdminRibbonApplication {
    public static void main(String[] args) {
        SpringApplication.run(WebAdminRibbonApplication.class, args);
    }
}

3.在 Ribbon 调用方法上增加 @HystrixCommand 注解并指定 fallbackMethod 熔断方法 

package com.lxq.hello.spring.cloud.web.admin.ribbon.service;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

/**
 * @Author Lxq
 * @Date 2020/3/29 13:43
 * @Version 1.0
 */
@Service
public class AdminService {

    @Autowired
    private RestTemplate restTemplate;

    @HystrixCommand(fallbackMethod = "hiError")
    public String sayHi(String message) {
        return restTemplate.getForObject("http://HELLO-SPRING-CLOUD-SERVICE-ADMIN/hi?message=" + message, String.class);
    }

    public String hiError(String message) {
        return "Hi，your message is :\"" + message + "\" but request error.";
    }
}

Feign使用熔断Hystrix

  fegin自带Hystrix但是默认关闭 需要手动开启
在application.yml 中加入
 

feign:
  hystrix:
    enabled: true

Fegin的熔断是通过调用一个自定义熔断类来实现对应的service服务接口类
所以创建一个熔断类 并且实现 相应的需要实现熔断的服务
别忘记要在所被实现的服务接口类的@FeignClient的属性增加fallback=所被实现的服务接口类.class

package com.lxq.hello.spring.cloud.web.admin.feign.service;

import com.lxq.hello.spring.cloud.web.admin.feign.service.hystrix.AdminServiceHystrix;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;

/**
 * @Author Lxq
 * @Date 2020/3/29 13:59
 * @Version 1.0
 * FeignClient:服务提供者的名称
 */
@FeignClient(value = "hello-spring-cloud-service-admin",fallback = AdminServiceHystrix.class)
public interface AdminService {

    @RequestMapping(value = "hi", method = RequestMethod.GET)
    String sayHi(@RequestParam("message") String message);
}

创建熔断类

package com.lxq.hello.spring.cloud.web.admin.feign.service.hystrix;

import com.lxq.hello.spring.cloud.web.admin.feign.service.AdminService;
import org.springframework.stereotype.Component;

/**
 * @Author Lxq
 * @Date 2020/3/29 14:20
 * @Version 1.0
 */
@Component
public class AdminServiceHystrix implements AdminService {


    @Override
    public String sayHi(String message) {
        return "Hi，your message is :\"" + message + "\" but request error.";
    }
}