SpringCloud之熔断器-Hystrix

墨蓝 2023-07-05 10:03 27阅读 0赞

Hystrix是一个延迟和容错库，旨在隔离对远程系统，服务和第三方库的访问点，停止级联故障，并在复杂的分布式系统中实现弹性，在这些系统中，故障是不可避免的。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg_size_16_color_FFFFFF_t_70]

## 依赖 ##

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

SpringBootApplication入口中需要添加`@EnableCircuitBreaker`注解，此时Spring工厂会启动AOP方式对所有的方法上有`@HystrixCommand`的业务方法添加熔断策略。

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

在业务方法上添加`@HystrixCommand`注解实现熔断。

@HystrixCommand
    @Override
    public User queryUserById(Integer id) { 
        System.out.println(Thread.currentThread().getId());
        return new User("未熔断", new Date(), true, 11.11);
    }

## 线程隔离 ##

默认该方法的执行会启动新的线程执行和主程序不在一个线程中，因此如果上下文中存在ThreadLocal变量，在该方法中就失效了。因此一般可以通过设置commandProperties注解属性，设置线程就可以了。

*  默认情况Service和Controller线程ID  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg_size_16_color_FFFFFF_t_70 1]

@HystrixCommand(commandProperties = { 
                @HystrixProperty(name = "execution.isolation.strategy",value = "SEMAPHORE")
        })
    @Override
    public User queryUserById(Integer id) { 
    	System.out.println("Service线程ID:" + Thread.currentThread().getId());
        return new User("未熔断", new Date(), true, 11.11);
    }

*  设置后Service和Controller线程ID  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg_size_16_color_FFFFFF_t_70 2]

> `execution.isolation.strategy`该属性的可选值有两个`THREAD`和`SEMAPHORE`默认值是`THREAD`。①一般如果一个实例一秒钟有100个并发，此时因为频繁启动线程的开销过大此时一般考虑使用SEMAPHORE，②非网络调用。

## Fallback ##

过在`@HystrixCommand中声明fallbackMethod`的名称可以实现优雅降级，如下所示：

@HystrixCommand(fallbackMethod = "fallbackMethodQueryUserById")
    @Override
    public User queryUserById(Integer id) { 
        System.out.println(Thread.currentThread().getId());
        int i=10/0;
        return new User("未熔断", new Date(), true, 11.11);
    }
    public User fallbackMethodQueryUserById(Integer id, Throwable e) { 
        System.out.println(e.getMessage());
        return new User("熔断降级后", new Date(), true, 11.11);
    }

调用结果：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg_size_16_color_FFFFFF_t_70 3]

> 注意要求fallbackMethod方法和目标方法必须在同一个类中，具有相同的参数（异常参数可选）

## Error Propagation ##

根据此描述，`@ HystrixCommand`能够指定应忽略的异常类型。如下所述`ArithmeticException: / by zero`将不会触发fallbackMethod方法。

// @HystrixCommand(fallbackMethod = "fallbackMethodQueryUserById")
    // @HystrixCommand(commandProperties = { 
    // @HystrixProperty(name = "execution.isolation.strategy", value = "SEMAPHORE")
    // })
    	@HystrixCommand(fallbackMethod = "fallbackMethodQueryUserById",ignoreExceptions = { ArithmeticException.class})
    	@Override
    	public User getUser(Integer id) { 
    		System.out.println("Service线程ID:" + Thread.currentThread().getId());
    		int i = 10 / 0;
    		return new User("未熔断", new Date(), true, 11.11);
    	}
    
    	public User fallbackMethodQueryUserById(Integer id, Throwable e) { 
    		System.out.println(e.getMessage());
    		return new User("熔断降级后", new Date(), true, 11.11);
    	}

## 请求超时熔断 ##

用户可以通过设置`execution.isolation.thread.timeoutInMilliseconds`属性设置一个方法最大请求延迟，系统会抛出`HystrixTimeoutException`

@HystrixCommand(fallbackMethod = "fallbackMethodQueryUserById",commandProperties = { 
    			@HystrixProperty(name="execution.isolation.thread.timeoutInMilliseconds",value="100")
    	})
    	@Override
    	public User getUser(Integer id) { 
    		System.out.println("Service线程ID:" + Thread.currentThread().getId());
    		try { 
    			Thread.sleep(500);
    		} catch (InterruptedException e) { 
    			e.printStackTrace();
    		}
    // int i = 10 / 0;
    		return new User("未熔断", new Date(), true, 11.11);
    	}
    
    	public User fallbackMethodQueryUserById(Integer id, Throwable e) { 
    		System.out.println(e.getMessage());
    		return new User("超时熔断", new Date(), true, 11.11);
    	}

执行结果：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg_size_16_color_FFFFFF_t_70 4]

> [https://github.com/Netflix/Hystrix/tree/master/hystrix-contrib/hystrix-javanica][https_github.com_Netflix_Hystrix_tree_master_hystrix-contrib_hystrix-javanica]  
> [https://github.com/Netflix/Hystrix/wiki/Configuration][https_github.com_Netflix_Hystrix_wiki_Configuration]

## Hystrix Dashboard ##

### 依赖 ###

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

> SpringBoot入口类添加`@EnableHystrixDashboard`注解  
> 访问页面http://localhost:端口/hystrix

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg_size_16_color_FFFFFF_t_70 5]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200213161905569.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg=,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/20200213165302950.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg=,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg_size_16_color_FFFFFF_t_70 2]: https://img-blog.csdnimg.cn/20200213165644697.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg=,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg_size_16_color_FFFFFF_t_70 3]: https://img-blog.csdnimg.cn/20200213170232834.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg=,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg_size_16_color_FFFFFF_t_70 4]: https://img-blog.csdnimg.cn/20200213171122722.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg=,size_16,color_FFFFFF,t_70
[https_github.com_Netflix_Hystrix_tree_master_hystrix-contrib_hystrix-javanica]: https://github.com/Netflix/Hystrix/tree/master/hystrix-contrib/hystrix-javanica
[https_github.com_Netflix_Hystrix_wiki_Configuration]: https://github.com/Netflix/Hystrix/wiki/Configuration
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg_size_16_color_FFFFFF_t_70 5]: https://img-blog.csdnimg.cn/20200213172042298.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L00yODM1OTIzMzg=,size_16,color_FFFFFF,t_70