一起来学SpringCloud之 - 断路器Hystrix（Ribbon）

微服务架构中，根据业务划分成若干个服务，各单元应用间通过服务注册与订阅的方式互相依赖，依赖通过远程调用的方式执行，该方式难以避免因网络或自身原因而出现故障或者延迟，从而并不能保证服务的100%可用，此时若有大量的网络涌入，会形成任务累计，导致服务瘫痪，甚至导致服务“雪崩”。

- Hystrix

1.Netflix 已经为我们创建了 Hystrix 库来实现服务降级、服务熔断、线程隔离、请求缓存、请求合并以及服务监控（Hystrix Dashboard）等强大功能，在微服务架构中，多层服务调用是非常常见的。

2.较底层的服务中的服务故障可能导致级联故障，当对特定的服务的调用达到一个阀值（Hystric 是5秒20次） 断路器将会被打开，故障百分比大于circuitBreaker.errorThresholdPercentage（默认值：> 50％）时metrics.rollingStats.timeInMilliseconds（默认10秒），断路打开后，开发人员可以回退机制。

官方文档： http://cloud.spring.io/spring-cloud-static/Dalston.SR2/#_circuit_breaker_hystrix_clients

- 准备工作

1.启动Consul

2.创建 battcn-provider 和 battcn-consumer

- battcn-provider

- pom.xml

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.battcn</groupId>
    <artifactId>battcn-provider</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>battcn-provider</name>
    <description>Ribbon与Hystrix</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <spring-cloud.version>Dalston.SR2</spring-cloud.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-consul-discovery</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </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>


</project>

- ProviderApplication.java

package com.battcn;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
@EnableDiscoveryClient
@RestController
public class ProviderApplication {

    @Value("${spring.application.name}")
    String applicationName;


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

    @GetMapping("/hello")
    public String hello() {
        return "My Name's :" + applicationName + " Email:1837307557@qq.com";
    }
}

- bootstrap.yml

server:
  port: 8765

spring:
  application:
    name: battcn-provider
  cloud:
    consul:
      host: localhost
      port: 8500
      enabled: true
      discovery:
        enabled: true
        prefer-ip-address: true

- battcn-consumer

- pom.xml

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.battcn</groupId>
    <artifactId>battcn-consumer</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>battcn-consumer</name>
    <description>Ribbon与Hystrix</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <spring-cloud.version>Dalston.SR2</spring-cloud.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-hystrix</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-consul-discovery</artifactId>
        </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>


</project>

- ConsumerApplication

package com.battcn;

import org.springframework.boot.SpringApplication;
import org.springframework.cloud.client.SpringCloudApplication;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

//@EnableDiscoveryClient
//@SpringBootApplication
//@EnableCircuitBreaker

/**
 * SpringCloudApplication 一个注解顶上面三个,有兴趣的可以点进去看源码
 */
@SpringCloudApplication
public class ConsumerApplication {

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

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

}

- HiController

package com.battcn.controller;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

/**
 * 为了偷懒，就写一个文件了
 */
@RestController
public class HiController {

    static Logger LOGGER = LoggerFactory.getLogger(HiController.class);
    @Autowired
    HiService hiService;

    @GetMapping("/hi")
    public String hi() {
        return hiService.hello();
    }

    @Service
    class HiService {
        @Autowired
        RestTemplate restTemplate;

        @HystrixCommand(fallbackMethod = "ribbonFallback")
        public String hello() {
            return restTemplate.getForObject("http://battcn-provider/hello", String.class);
        }

        public String ribbonFallback() {
            return "My Name's :ribbonFallback Email:1837307557@qq.com";
        }
    }

}

- bootstrap.yml

server:
  port: 8766

spring:
  application:
    name: battcn-consumer
  cloud:
    consul:
      host: localhost
      port: 8500
      enabled: true
      discovery:
        enabled: true
        prefer-ip-address: true

- 测试

启动：battcn-provider

启动：battcn-consumer

访问： http://localhost:8500/ 显示如下代表服务注册成功

访问： http://localhost:8766/hi

My Name's :battcn-provider Email:1837307557@qq.com    #正确情况

My Name's :ribbonFallback Email:1837307557@qq.com    #关闭battcn-provider后结果

- 源码

1.当我们开启 Hystrix 的时候 Hystrix 会为我们注入 HystrixCommandAspect 切面，操作所有带 HystrixCommand 注解，随后就是通过反射与Cglib创建代理然后发送请求，不管服务是否健壮都会先进入AOP切面然后才会执行后续操作（打脸轻点…）

- 监控

1.在 ConsumerApplication 中添加 @EnableHystrixDashboard 的注解

@SpringCloudApplication
@EnableHystrixDashboard    //多了个开启监控注解
public class ConsumerApplication {

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

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

}

2.在 pom.xml 中添加如下配置

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

3.访问： http://localhost:8766/hystrix

4.访问N次： http://localhost:8766/hi

我们可以看到请求成功，失败，等信息

- 说点什么

本章代码（battcn-provider/consumer）： https://git.oschina.net/battcn/battcn-cloud/tree/master/battcn-cloud-hystrix-ribbon

如有问题请及时与我联系

1. 个人QQ：1837307557
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