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可以用feign方式和RestTemplate+ribbon方式来实现服务间的相互调用。但如果某一个服务出现问题，所有调用该出问题的服务都将出现阻塞，如果有大量的请求，则Servlet容器的线程资源会被消耗完毕，导致服务瘫痪。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造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

因为feign是自带断路器的，所以依赖中就不需要加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，但需要打开

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

出现以下两种场景：

和

如果关掉8792端口的服务，则会返回hi,I am port 8793

如果关掉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。

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