熔断器 Hystrix

熔断器Hystrix

版本 2.2.1.RELEASE

1. 介绍

 Hystrix是一个延迟和容错工具，旨在隔离远程系统，服务以及第三方库，阻止级联故障，在复杂的分布式系统中实现恢复能力。


 Hysrix的设计目标:

1. 对延迟和故障进行隔离保护
2. 在一个复杂的分布式系统中防止级联故障
3. 快速失败(防止阻塞)和快速恢复
4. 回退和优雅的降级
5. 开启近实时监控，报警和操作控制

2. 流程图 hystrix-command-flow-chart.png

1. 创建一个HystrixCommand或者HystrixObservableCommand对象
2. 执行command命令
3. 判断缓存是否可用
4. 判断短路器是否处于打开状态
5. 判断线程池/队列/信号量是否已经达到最大值
6. 执行HystrixCommand中的目标方法
7. 根据目标方法的返回情况决定短路器是否打开
8. 获取fallback返回对象
9. 获取正常的返回对象

3. 简单上手

spring-hystrix

 引入相关依赖

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

 在启动类上添加注解@EnableHystrix

@EnableHystrix
@EnableDiscoveryClient
@SpringBootApplication
public class CloudHystrixApplication {
    public static void main(String[] args) {
        SpringApplication.run(CloudHystrixApplication.class, args);
    }
}

在需要进行熔断保护的方法上添加@HystrixCommand注解

    @ResponseBody
    @RequestMapping(value = "/getUser", method = RequestMethod.GET)
    @HystrixCommand(fallbackMethod = "defaultUser")
    public String getUser(String userName) throws Exception{
        if("wang".equals(userName)){
            return "this is real user";
        } else {
            throw new Exception("123");
        }
    }

    /**
     * hystrix的fallback方法
     * @param userName
     * @return
     */
    public String defaultUser(String userName){
        return "The user does not exist";
    }

 启动工程，当输入错误的参数时，就会返回fallback方法的对象

hystrix配合feign使用

 feign内嵌了Hystrix和Eureka，所以就使用feign的依赖即可

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

 在启动类上增加@EnableFeignClients注解

@EnableDiscoveryClient
@SpringBootApplication
@EnableFeignClients
public class CloudEurekaClientApplication {
    public static void main(String[] args) {
        SpringApplication.run(CloudEurekaClientApplication.class, args);
    }
}

 新增feign接口，调用目标服务的url，接口上添加@FeignClient注解

@FeignClient(name = "Hystrix", fallback = HystrixFallback.class)
public interface Hystrix {
    @RequestMapping(value = "/getUser", method = RequestMethod.GET)
    String getUser(@RequestParam("userName") String userName);
}

 同时，创建实现类实现该接口，在实现类中实现fallback返回对象，实现类要用@Component注解修饰

@Component
public class HystrixFallback implements Hystrix {
    @Override
    public String getUser(String userName) {
        return "the user does not exist in this system";
    }
}

 在需要调用该接口的类中自动注入该接口

@Controller
public class UserController {

    @Autowired
    private Hystrix hystrixClient;

    @ResponseBody
    @RequestMapping(value = "/getUser", method = RequestMethod.GET)
    public String getUser(String userName){
        String user = hystrixClient.getUser(userName);
        return user;
    }
}

 在该工程的properties文件新增下列语句，开启feign的Hystrix

feign.hystrix.enabled=true

 启动工程，调用对应的url，如果参数输入错误，如果被调用方出现异常，则返回HystrixFallback实现的fallback对象

Hystrix-Dashboard

 新建一个工程，引入dashboard相关依赖

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

 在启动类上添加@EnableHystrixDashboard注解

@EnableHystrixDashboard
@SpringBootApplication
@EnableDiscoveryClient
public class CloudHystrixDashboardApplication {
    public static void main(String[] args) {
        SpringApplication.run(CloudHystrixDashboardApplication.class, args);
    }
}

 浏览器输入对应的网址ip:port/hystrix即可访问dashboard页面 image.png

Hystrix或者Feign如何整合dashboard

 在hystrix工程的依赖中添加spring-actuator依赖

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

 在该工程的properties文件中新增如下语句

management.endpoints.web.exposure.include=hystrix.stream

 将http://localhost:8081/actuator/hystrix.stream输入到dashboard页面中的地址栏中，点击monitor stream按钮即可进入监控页面

image.png

feign整合dashboard

 和上面hystrix整合dashboard原理差不多，只是在启动类上除了有@FeignClients还需要添加@EnableHystrix注解

@EnableDiscoveryClient
@SpringBootApplication
@EnableFeignClients
@EnableHystrix
public class CloudEurekaClientApplication {
    public static void main(String[] args) {
        SpringApplication.run(CloudEurekaClientApplication.class, args);
    }
}