Spring-Cloud-Finchley | 熔断 Hystrix

简介

熔断机制产生的背景是“雪崩效应”，在分布式系统中，一个服务提供者的不可用会导致服务消费者的不可用，一个服务的异常，最终会影响其他服务，造成线程阻塞，资源耗尽，如果有大量的请求，会导致服务瘫痪，引蝴蝶效应造成系统宕机。

如果一个服务的错误过多，短时间内得不到修复，就可以开启熔断机制，防止多次没有意义的调用。服务调用方会定时重试，如果可用，就继续使用。

熔断有以下几种状态：

• 闭合状态
  添加一个计数器，如果失败的次数在指定时间内超过一定阈值，则开启熔断，此时处于断开状态，此时开启一个计时器，如果过了指定时间，则切换到半断开，服务可被尝试调用。

• 断开状态
  服务如果被调用会立即返回错误信息，减少资源损耗。

• 半开状态
  允许一定数量的请求调用服务，如果请求调用成功，则关闭熔断，认为服务的错误已经修正。如果还是发生错误，则切换到断开状态。

实例

1、搭建 maven 环境

Hystrix 是知名视频网站 Netflix 开源的框架，完美解决了分布式系统中所面临的这个技术问题，解决了雪崩效应。

首先搭建 maven 环境，父 pom 如下

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
    <spring-cloud.version>Finchley.RELEASE</spring-cloud.version>
  </properties>

  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.0.5.RELEASE</version>
    <relativePath/>
  </parent>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </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>

2、搭建服务注册中心 eureka-server

maven 依赖

	<parent>
		<groupId>com.hly</groupId>
		<artifactId>04-spring-cloud-hystrix</artifactId>
		<version>1.0-SNAPSHOT</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>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
	</dependencies>

application.yml 配置文件

server:
  port: 8761

eureka:
  instance:
    hostname: localhost
  client:
    registerWithEureka: false
    fetchRegistry: false
    serviceUrl:
      defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/

spring:
  application:
    name: service-server

SpringBoot 启动类

@SpringBootApplication
@EnableEurekaServer
public class ServiceServerApplication {

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

3、搭建服务提供者 client

maven 依赖

	<parent>
		<groupId>com.hly</groupId>
		<artifactId>04-spring-cloud-hystrix</artifactId>
		<version>1.0-SNAPSHOT</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>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
	</dependencies>

application.yml

server:
  port: 8762

spring:
  application:
    name: service-client

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/

SpringBoot 启动类

@SpringBootApplication
@RestController
@EnableEurekaClient
public class ServiceClientApplication {

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

	@Value("${server.port}")
	String port;
	@RequestMapping("/hello")
	public String home(@RequestParam(value = "name", defaultValue = "hly") String name) {
		return "hi " + name + " ,i am from port:" + port;
	}
}

4、搭建服务消费者 feign 客户端

maven 依赖

	<parent>
		<groupId>com.hly</groupId>
		<artifactId>04-spring-cloud-hystrix</artifactId>
		<version>1.0-SNAPSHOT</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>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-openfeign</artifactId>
		</dependency>
	</dependencies>

application.yml

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
server:
  port: 8765
spring:
  application:
    name: service-feign

# 开启熔断
feign:
  hystrix:
    enabled : true

服务层接口

//服务名指定调用哪个服务
@FeignClient(value = "service-client",fallback =HiHystrixServiceImpl.class)
public interface HiHystrixService {
    //这里的映射名和需要调用的服务的映射名一样
    @RequestMapping(value = "/hello",method = RequestMethod.GET)
    String sayHiFromClientOne(@RequestParam(value = "name") String name);
}

指定实行快速失败的方法

@Component
public class HiHystrixServiceImpl implements HiHystrixService {
    @Override
    public String sayHiFromClientOne(String name) {
        return "sorry"+name;
    }
}

Controller 层

@RestController
public class HiController {

   @Autowired
   HiHystrixService hiHystrixService;

    /**
     * 消费服务
     * @param name
     * @return
     */
    @GetMapping(value = "/hi")
    public String sayHi(@RequestParam String name) {
        return hiHystrixService.sayHiFromClientOne( name );
    }
}

SpringBoot 启动类

@SpringBootApplication
@EnableEurekaClient
@EnableDiscoveryClient
@EnableFeignClients
public class ServiceFeignHystrixApplication {

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

演示

1、依次启动 注册中心 server ，启动两个 client(启动一个后，修改application.yml 配置文件的端口，再次启动一次)，接着启动 Feign 客户端，访问：
http://localhost:8765/hi?name=hly
当关掉客户端后，将会执行快速失败策略。

代码下载

04-spring-cloud-hystrix：https://github.com/huangliangyun/Spring-Cloud-Finchley

关于

我的 Github：Github
CSDN: CSDN
个人网站: sirius 的博客
E-mail: [email protected]

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