学习微服务的断路器——hystrix

微服务架构中，微服务之间相互调用，springcloud能够用feign方式和RestTemplate+ribbon方式来实现服务间的相互调用。但若是某一个服务出现问题，全部调用该出问题的服务都将出现阻塞，若是有大量的请求，则Servlet容器的线程资源会被消耗完毕，致使服务瘫痪。服务与服务之间的依赖性，故障会传播，会对整个微服务系统形成灾难性的严重后果，这就是服务故障的“雪崩”效应。

为了解决这个问题，业界提出了断路器模型。

1.ribbon中使用断路器hystrix

build.gradle文件

buildscript {
	ext {
		springBootVersion = '2.0.4.RELEASE'
	}
	repositories {
		mavenCentral()
	}
	dependencies {
		classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
	}
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'

group = 'com.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = 1.8

repositories {
	mavenCentral()
}


ext {
	springCloudVersion = 'Finchley.SR1'
}

dependencies {
	compile('org.springframework.boot:spring-boot-starter-web')
	compile('org.springframework.cloud:spring-cloud-starter-netflix-eureka-client')
	compile('org.springframework.cloud:spring-cloud-starter-netflix-hystrix')
	compile('org.springframework.cloud:spring-cloud-starter-netflix-ribbon')
	testCompile('org.springframework.boot:spring-boot-starter-test')
}

dependencyManagement {
	imports {
		mavenBom "org.springframework.cloud:spring-cloud-dependencies:${springCloudVersion}"
	}
}

application.yml文件

server:
  port: 8797

spring:
  application:
    name: service-ribbon-hystrix

eureka:
  client:
    service-url:
      defaultZone: http://localhost:8791/eureka/

主方法

package com.example.serviceribbonhystrix;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
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 ServiceRibbonHystrixApplication {

	public static void main(String[] args) {
		SpringApplication.run(ServiceRibbonHystrixApplication.class, args);
	}


	@Bean
	RestTemplate restTemplate() {
		return new RestTemplate();
	}
}

HelloService.java文件

package com.example.serviceribbonhystrix;

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;

@Service
public class HelloService {

    @Autowired
    RestTemplate restTemplate;


    @HystrixCommand(fallbackMethod = "errorMsg")
    public String hiService() {
        return restTemplate.getForObject("http://EUREKA-CLIENT-SAY-HI/hi", String.class);
    }


    public String errorMsg(){
        return "I am ribbon with hystrix,Wrong!";
    }
}

HelloController.java文件

package com.example.serviceribbonhystrix;


import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {
    @Autowired
    HelloService helloService;

    @RequestMapping("/hi")
    public String sayHi() {
        return helloService.hiService();
    }


}

只是单独启动该服务，不启动eureka-client-say-hi服务，访问http://localhost:8797/hi

返回要返回的信息，此时断路器已经生效了：

2.feign中使用断路器hystrix

由于feign是自带断路器的，因此依赖中就不须要加hystrix

build.gradle

buildscript {
    ext {
        springBootVersion = '2.0.4.RELEASE'
    }
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
    }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'

group = 'com.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = 1.8

repositories {
    mavenCentral()
}


ext {
    springCloudVersion = 'Finchley.SR1'
}

dependencies {
    compile('org.springframework.boot:spring-boot-starter-web')
    compile('org.springframework.cloud:spring-cloud-starter-netflix-eureka-client')
    compile('org.springframework.cloud:spring-cloud-starter-openfeign')
    testCompile('org.springframework.boot:spring-boot-starter-test')
}

dependencyManagement {
    imports {
        mavenBom "org.springframework.cloud:spring-cloud-dependencies:${springCloudVersion}"
    }
}

application.yml文件

server:
  port: 8796


spring:
  application:
    name: service-feign-hystrix


eureka:
  client:
    service-url:
      defaultZone: http://localhost:8791/eureka/


feign:
  hystrix:
    enabled: true  #feign自带断路器，但须要打开

主方法：

package com.example.servicefeignhystrix;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.openfeign.EnableFeignClients;

@EnableEurekaClient
@EnableFeignClients
@SpringBootApplication
public class ServiceFeignHystrixApplication {

	public static void main(String[] args) {
		SpringApplication.run(ServiceFeignHystrixApplication.class, args);
	}
}

接口SayHiService.java文件

package com.example.servicefeignhystrix;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@FeignClient(value = "eureka-client-say-hi",fallback = SayHiServiceWithHystrix.class)
public interface SayHiService {

    @RequestMapping(value = "/hi", method = RequestMethod.GET)
    String sayHiFromClient();


}

SayHiServiceWithHystrix.java文件

package com.example.servicefeignhystrix;

import org.springframework.stereotype.Component;

@Component
public class SayHiServiceWithHystrix implements SayHiService {
    @Override
    public String sayHiFromClient() {
        return "sorry,I am wrong";
    }
}

HelloController.java文件

package com.example.servicefeignhystrix;


import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {




    @Autowired
    SayHiService sayHiService;

    @RequestMapping("/hi")
    public String sayHi(){
        return sayHiService.sayHiFromClient();
    }
}

此时启动eureka-server，以及eureka-client-say-hi项目的两个实例，以及刚才新建的项目service-feign-hystrix.

访问http://localhost:8796/hi

出现如下两种场景：

和

若是关掉8792端口的服务，则会返回hi,I am port 8793

若是关掉eureka-client-say-hi服务的8792和8793两个端口实例，则会返回

此时标明，feign的断路器已经生效了。