學習微服務的斷路器——hystrix

微服務架構中，微服務之間相互調用，springcloud能夠用feign方式和RestTemplate+ribbon方式來實現服務間的相互調用。但若是某一個服務出現問題，全部調用該出問題的服務都將出現阻塞，若是有大量的請求，則Servlet容器的線程資源會被消耗完畢，致使服務癱瘓。服務與服務之間的依賴性，故障會傳播，會對整個微服務系統形成災難性的嚴重後果，這就是服務故障的「雪崩」效應。

爲了解決這個問題，業界提出了斷路器模型。

1.ribbon中使用斷路器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();
    }


}

只是單獨啓動該服務，不啓動eureka-client-say-hi服務，訪問http://localhost:8797/hi

返回要返回的信息，此時斷路器已經生效了：

2.feign中使用斷路器hystrix

由於feign是自帶斷路器的，因此依賴中就不須要加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自帶斷路器，但須要打開

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();
    }
}

此時啓動eureka-server，以及eureka-client-say-hi項目的兩個實例，以及剛纔新建的項目service-feign-hystrix.

訪問http://localhost:8796/hi

出現如下兩種場景：

和

若是關掉8792端口的服務，則會返回hi,I am port 8793

若是關掉eureka-client-say-hi服務的8792和8793兩個端口實例，則會返回

此時標明，feign的斷路器已經生效了。