1.服务雪崩

多个微服务之间调用的时候，假设服务A调用服务B和服务C，服务B和服务C 又调用其他服务，这就是所谓的“扇出”。如果扇出的链路上某个服务调用时间过长或根本不可用，对服务A的调用就会占用越来越多的系统资源，进而引起崩溃，所谓的“雪崩效应”。

对于高流量的应用来说，单一的后端依赖可能会导致所有服务器上的所有资源在几秒钟内饱和。比失败更糟糕的是，这些应用程序还可能导致服务之间的延迟增加，备份队列，线程和洽系统资源紧张，导致整个系统发生更多的级联故障。这些都表示需要对故障和延迟进行隔离和管理，以便单个依赖关系的失败，不能取消整个应用程序或系统。所以，通常当你发现一个模块下的某个实例失败后，这时候这个模块依然还会接受流量，然后这个有问题的模块还调用了其他模块，这样就会发生级联故障，或者叫雪崩。

2.Hystrix是什么

Hystrix是一个用于处理分布式系统的延迟和容错的开源库，在分布式系统里，许多依赖不可避免的会调用失败，比如超时、异常等，Hystrix能够保证在一个依赖出问题的情况下，不会导致整体服务失败，避免级联故障，以提高分布式系统的弹性。“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、不必要的占用，从而避免了故障在分布式系统中的蔓延，乃至雪崩。

3.新建项目cloud-hystrix-consumer-8005

pom

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.3.5.RELEASE</version><relativePath/> <!-- lookup parent from repository --></parent><groupId>com.yinuo</groupId><artifactId>cloud-hystrix-consumer-8005</artifactId><version>0.0.1-SNAPSHOT</version><name>cloud-hystrix-consumer-8005</name><description>Demo project for Spring Boot</description><properties><java.version>1.8</java.version><spring-cloud.version>Hoxton.SR9</spring-cloud.version></properties><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-netflix-hystrix</artifactId></dependency><!--openfeign--><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-openfeign</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-actuator</artifactId></dependency><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-netflix-eureka-client</artifactId></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><optional>true</optional></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency></dependencies><dependencyManagement><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-dependencies</artifactId><version>${spring-cloud.version}</version><type>pom</type><scope>import</scope></dependency></dependencies></dependencyManagement><build><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId></plugin></plugins></build><repositories><repository><id>spring-milestones</id><name>Spring Milestones</name><url>https://repo.spring.io/milestone</url></repository></repositories></project>

yml

server:port: 8006
spring:application:name: hytrix-consumerdevtools:restart:enabled: true #开启热部署
eureka:client:fetchRegistry: true #是否从eurekaServer中抓取已有的注册信息，默认为ture，单节点无所谓，集群必须为ture才能配合ribbon使用负载均衡register-with-eureka: true #注册进eurekaServerservice-url:defaultZone: http://eureka-8091:8091/eureka/,http://eureka-8092:8092/eureka/instance:instance-id: hytrix-consumer-8006prefer-ip-address: true #显示IP地址feign:hystrix:enabled: true #开启feign的hystrix支持,默认是false

启动类

package com.yinuo.consumer8005;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;
import org.springframework.cloud.openfeign.EnableFeignClients;@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
@EnableHystrix
public class CloudHystrixConsumer8005Application {public static void main(String[] args) {SpringApplication.run(CloudHystrixConsumer8005Application.class, args);}}

 

 4.新建HystrixService

package com.yinuo.consumer8005.sevice;import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.RequestMapping;@FeignClient(value = "cloud-payment")//要调取的服务名
@Component
public interface HystrixService {@RequestMapping("/get")//这是8001和8002的TestController里的get接口public String get();@RequestMapping("/timeOut")public String timeOut();
}

5.新建HystrixController

package com.yinuo.consumer8005.controller;import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixProperty;
import com.yinuo.consumer8006.sevice.HystrixService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;@RestController
public class HystrixController {@AutowiredHystrixService service;@RequestMapping("/consumer/get")public String get(){return service.get();}/*** hystrixTimeOutFallback降级的方法名** **/@RequestMapping("/consumer/timeOut")@HystrixCommand(fallbackMethod = "hystrixTimeOutFallback",commandProperties = {@HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds",value = "1500")//表示连接1.5秒没有响应后进行降级处理})public String timeOut(){return service.timeOut();}/*** hystrixTimeOutFallback降级的方法名** **/@RequestMapping("/consumer/getError")@HystrixCommand(fallbackMethod = "hystrixTimeOutFallback",commandProperties = {@HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds",value = "1500")//表示连接1.5秒没有响应后进行降级处理})public String getError(){int i=10/0;//故意报错，测试降级return "666666666666666666";}/*** 降级方法** **/public String hystrixTimeOutFallback(){return "服务进行降级了，O(∩_∩)O哈哈~";}
}

6.访问http://localhost:8005/consumer/timeOut和http://localhost:8006/consumer/getError

 

7.在实际的工作中，每个方法配置一个服务降级方法，技术上可以，实际上不会出现这种类似于傻x的行为。实际工作中除了个别重要的核心业务，其他的普通的可以通过@DefaultProperties(defaultFallback = "")注解统一跳转到一个统一的处理结果页面。通用的和独享的个子分开，避免了代码的膨胀，合理减少了代码量。

 8.HystrixController增加@DefaultProperties(defaultFallback = "global_fallback")，global_fallback为全局降级方法名

package com.yinuo.consumer8005.controller;import com.netflix.hystrix.contrib.javanica.annotation.DefaultProperties;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixProperty;
import com.yinuo.consumer8006.sevice.HystrixService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;@RestController
@DefaultProperties(defaultFallback = "global_fallback")//global_fallback全局降级方法名
public class HystrixController {@AutowiredHystrixService service;@RequestMapping("/consumer/get")public String get(){return service.get();}/*** hystrixTimeOutFallback降级的方法名** **/@RequestMapping("/consumer/timeOut")@HystrixCommand(fallbackMethod = "hystrixTimeOutFallback",commandProperties = {@HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds",value = "1500")//表示连接1.5秒没有响应后进行降级处理})public String timeOut(){return service.timeOut();}/*** hystrixTimeOutFallback降级的方法名** **/@RequestMapping("/consumer/getError")@HystrixCommand(fallbackMethod = "hystrixTimeOutFallback",commandProperties = {@HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds",value = "1500")//表示连接1.5秒没有响应后进行降级处理})public String getError(){int i=10/0;//故意报错，测试降级return "666666666666666666";}/*** 降级方法** **/public String hystrixTimeOutFallback(){return "服务进行降级了，O(∩_∩)O哈哈~";}@RequestMapping("consumer/global/timeOut")@HystrixCommandpublic String global(){return service.timeOut();}@RequestMapping("/consumer/global/getError")@HystrixCommandpublic String getGlobalError(){int i=10/0;//故意报错，测试降级return "666666666666666666";}/*** 降级方法** **/public String global_fallback(){return "=================统一服务进行降级了，O(∩_∩)O哈哈~";}
}

9.访问http://localhost:8005/consumer/global/timeOut和http://localhost:8006/consumer/global/getError

10.因为项目中引用了Feign，在实际的工作中，为了解耦，通常不会在controller层做一些操作，所以，在HystrixService的@FeignClient注解上增加fallback来处理调取这个微服务的降级处理

11.新增HystrixServiceFallbackService

package com.yinuo.consumer8006.sevice;import org.springframework.stereotype.Component;@Component
public class HystrixServiceFallbackService implements HystrixService{@Overridepublic String get() {return "get fallback 服务降级===========";}@Overridepublic String timeOut() {return "==========timeOut fallback 服务降级===========";}
}

12.HystrixService中的@FeiginClint注解增加fallback

@FeignClient(value = "cloud-payment",fallback = HystrixServiceFallbackService.class)//要调取的服务名

13.新增FeignFallbackController

package com.yinuo.consumer8006.controller;import com.yinuo.consumer8006.sevice.HystrixService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;@RestController
public class FeignFallbackController {@Autowiredprivate HystrixService service;@RequestMapping("consumer/feignFallback/get")public String get(){return service.get();}@RequestMapping("consumer/feignFallback/timeOut")public String timeOut(){return service.timeOut();}
}

14.停掉cloud-payment的两个服务，访问http://localhost:8005/consumer/feignFallback/timeOut和http://localhost:8005/consumer/feignFallback/get，可以看到controller层未加任何hytirx注解，也会进行降级处理。

 

注：若使用@FeignClient的fallback，yml文件中必须开启feign对hytrix的支持

feign:hystrix:enabled: true #开启feign的hystrix支持,默认是false