SpringCloud系列教程05-断路器之Hystrix

Bertha 。 2024-04-17 21:44 72阅读 0赞

### 文章目录 ###

*   *  service-producer
     *  基于Feign使用Hystrix
     *  基于Ribbon使用Hystrix
     *  项目源码
     *  参考

--------------------

在没有良好异常处理机制的微服务架构中，可以预见的是，一旦某个服务发生故障，依赖于此服务的服务就会产生连环性的破坏，导致“雪崩效应”。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzI4Mzc5ODA5_size_16_color_FFFFFF_t_70]

为了解决这一问题，提出了`断路器`的概念。

官网：

> Netflix has created a library called [Hystrix][] that implements the [circuit breaker pattern][]. In a microservice architecture, it is common to have multiple layers of service calls, as shown in the following example:

Netflix提供了Hystrix库，用于实现断路器模型。在微服务架构中，通常有多层服务调用。

下面的示例演示了`Hystrix`分别在ribbon和feign这两种服务调用方式中的配合使用。

本示例采用`SpringBoot 2.1.7.RELEASE`和`SpringCloud Greenwich.SR2`。在使用SpringBoot2.0.x和SpringCloud Finchley.RELEASE版本时，发现Feign的Hystrix开启配置是没有提示的（也会生效，但是没有代码提示，很奇怪。所以把版本换成SpringBoot 2.0.x和SpringCloud Finchley.RELEASE也可以正常运行的）

本节依然使用consul做服务中心。

--------------------

## service-producer ##

首先创建一个服务提供者`service-producer`，引入`consul-discovery`依赖，并添加一个测试接口即可。（与之前的教程基本一致）

这里不具体描述了，可以直接看源码：https://github.com/laolunsi/spring-cloud-examples/tree/master/05-ServiceHystrix/service-producer

或者参考之前的教程

下面我们就在使用feign和ribbon这两种服务调用方式中，分别如何去使用断路器Hystrix。

--------------------

## 基于Feign使用Hystrix ##

引入`consul`、`feign`和`hystrix`的依赖：

<properties>
            <java.version>1.8</java.version>
            
            <spring-cloud.version>Greenwich.SR2</spring-cloud.version>
        </properties>
    
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-web</artifactId>
            </dependency>
    
            
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-starter-consul-discovery</artifactId>
            </dependency>
    
            
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-starter-openfeign</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-netflix-hystrix</artifactId>
            </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>

注意这里使用的SpringCloud版本是`Greenwich.SR2`，与之对应的SpringBoot版本是2.1.x.RELEASE

配置：

server:
      port: 8510
    spring:
      application:
        name: service-consumer-feign
      cloud:
        consul:
          host: localhost
          port: 8500
          discovery:
            register: true
            instance-id: ${ spring.application.name}:${ server.port}
            service-name: ${ spring.application.name}
            port: ${ server.port}
    # 加入这个配置，用于启动feign自带的断路器
    feign:
      hystrix:
        enabled: true

修改启动类：

package com.example.serviceconsumerfeign;
    
    import org.springframework.boot.SpringApplication;
    import org.springframework.boot.autoconfigure.SpringBootApplication;
    import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
    import org.springframework.cloud.netflix.hystrix.EnableHystrix;
    import org.springframework.cloud.openfeign.EnableFeignClients;
    
    @SpringBootApplication
    @EnableDiscoveryClient
    @EnableFeignClients
    /*@EnableHystrix*/
    public class ServiceConsumerFeignApplication { 
    
        public static void main(String[] args) { 
            SpringApplication.run(ServiceConsumerFeignApplication.class, args);
        }
    
    }

注：在配置文件中我们启用了Feign自带的Hystrix，所以即使启动类不写@EnableHystrix，断路器依然会起作用。

下面编写测试Feign的测试接口和API（与之前的教程相同）：

package com.example.serviceconsumerfeign;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.web.bind.annotation.GetMapping;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.bind.annotation.RestController;
    
    @RestController
    @RequestMapping(value = "consumer/feign")
    public class ConsumerAction { 
    
        @Autowired
        private ProducerApi producerApi;
    
        @GetMapping(value = "test")
        public String test(String name) { 
            String producerRes = producerApi.hello(name);
            String res = "测试consumer/test接口，基于feign调取服务server-producer的hello接口，返回：" + producerRes;
            System.out.println(res);
            return res;
        }
    }

Api类：

package com.example.serviceconsumerfeign;
    
    import org.springframework.cloud.openfeign.FeignClient;
    import org.springframework.web.bind.annotation.GetMapping;
    import org.springframework.web.bind.annotation.PathVariable;
    
    /** * 调用service-producer服务接口 */
    @FeignClient(name = "service-producer", fallback = ProducerApiHystrix.class)
    public interface ProducerApi { 
    
        @GetMapping(value = "producer/hello/{name}")
        public String hello(@PathVariable("name") String name);
    }

看到了没有，上面的`@FeignClient`注解中，我添加了一个fallback属性，它的值对应一个自定义的class——`ProducerApiHystrix`。

下面我们来实现这个class：

package com.example.serviceconsumerfeign;
    
    import org.springframework.stereotype.Component;
    
    /** * ProducerApi对应的断路器 */
    @Component
    public class ProducerApiHystrix implements ProducerApi { 
    
        @Override
        public String hello(String name) { 
            return "sorry, " + name + ", this service is unavailable temporarily. We are returning the defaultValue by hystrix.";
        }
    }

这就是断路器类，它实际上是`ProducerApi`的实现类，实现了后者需要调用的接口。那么，当请求发生异常、超时等情况时，Hysytix就会使得这个类生效，返回一个默认值。

而如果使用断路器，我们来测试看看：

1.  正常情况：

![在这里插入图片描述][20190901184155285.png]

1.  异常情况，比如我们关掉service-producer：  
    ![在这里插入图片描述][20190901184205638.png]

而如果不使用断路器，且被调用的服务断了，那么会报异常：

`com.netflix.client.ClientException: Load balancer does not have available server for client: service-producer`

--------------------

## 基于Ribbon使用Hystrix ##

基于ribbon使用hystrix，相比于feign更加简单：

引入依赖`consul-discovery`、`ribbon`、`hystrix`：

<properties>
            <java.version>1.8</java.version>
            <spring-cloud.version>Greenwich.SR2</spring-cloud.version>
        </properties>
    
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-web</artifactId>
            </dependency>
    
            
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-starter-consul-discovery</artifactId>
            </dependency>
    
            
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-starter-netflix-ribbon</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-netflix-hystrix</artifactId>
            </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>

配置文件不需要修改：

server:
      port: 8511
    spring:
      application:
        name: service-consumer-ribbon
      cloud:
        consul:
          host: localhost
          port: 8500
          discovery:
            instance-id: ${ spring.application.name}:${ server.port}
            port: ${ server.port}
            service-name: ${ spring.application.name}
            register: true

使用@EnableHystrix注解开启断路器：

@SpringBootApplication
    @EnableDiscoveryClient
    @EnableHystrix
    public class ServiceConsumerRibbonApplication { 
    
        public static void main(String[] args) { 
            SpringApplication.run(ServiceConsumerRibbonApplication.class, args);
        }
    
        /** * 注入RestTemplate Bean，并开启负载均衡 * @return */
        @Bean
        @LoadBalanced
        public RestTemplate restTemplate() { 
            return new RestTemplate();
        }
    
    }

编写测试接口和对应的断路器：

package com.example.serviceconsumerribbon;
    
    import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.web.bind.annotation.GetMapping;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.bind.annotation.RestController;
    import org.springframework.web.client.RestTemplate;
    
    @RestController
    @RequestMapping(value = "consumer/ribbon")
    public class ConsumerAction { 
    
        @Autowired
        private RestTemplate restTemplate;
    
        private static final String service_producer_name = "service-producer";
    
        @GetMapping(value = "test")
        @HystrixCommand(fallbackMethod = "testHystrix")
        public String test(String name) { 
            String producerRes = restTemplate.getForObject(
                    "http://" + service_producer_name + "/producer/hello/" + name, String.class);
            String res = "测试consumer/test接口，基于ribbon调取服务server-producer的hello接口，返回：" + producerRes;
            System.out.println(res);
            return res;
        }
    
        /** * test接口的断路器 */
        private String testHystrix(String name) { 
            return "sorry, " + name + ", this service is unavailable temporarily. We are returning the defaultValue by hystrix.";
        }
    }

我们可以看到，ribbon服务调用中，断路器Hystrix是使用`@HystrixCommand`注解在方法上进行的，对应的属性是`fallBackMethod`，然后我们只要实现这个方法即可。

测试：

1.  正常情况：

![在这里插入图片描述][20190901184238867.png]

1.  异常情况，比如关闭service-producer：

![在这里插入图片描述][20190901184250792.png]

如果没有开启断路器，而请求未开启服务的接口，就会报错：

`java.lang.IllegalStateException: Request URI does not contain a valid hostname: http://service_producer/producer/hello/ye`

--------------------

## 项目源码 ##

[https://github.com/laolunsi/spring-cloud-examples/tree/master/05-ServiceHystrix][https_github.com_laolunsi_spring-cloud-examples_tree_master_05-ServiceHystrix]

--------------------

## 参考 ##

> 1.  方志朋-SpringCloud第四篇-断路器(Hystrix)\[Finchley版\]：[https://blog.csdn.net/forezp/article/details/81040990][https_blog.csdn.net_forezp_article_details_81040990]
> 2.  纯洁的微笑-SpringCloud(4)-熔断器(Hystrix)：[http://www.ityouknow.com/springcloud/2017/05/16/springcloud-hystrix.html][http_www.ityouknow.com_springcloud_2017_05_16_springcloud-hystrix.html]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzI4Mzc5ODA5_size_16_color_FFFFFF_t_70]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/97eef4f0f4b142ad801d68738f1fff39.png
[Hystrix]: https://github.com/Netflix/Hystrix
[circuit breaker pattern]: https://martinfowler.com/bliki/CircuitBreaker.html
[20190901184155285.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/717aa5c7568b41e19b21452d219bfa95.png
[20190901184205638.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/64adda6ed4e0467a9aa6ddbfbff3dd5f.png
[20190901184238867.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/159829fab4674fed8c0d395cfb668fb8.png
[20190901184250792.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/372b3a6a1ac047908ad108ea2e8e3e65.png
[https_github.com_laolunsi_spring-cloud-examples_tree_master_05-ServiceHystrix]: https://github.com/laolunsi/spring-cloud-examples/tree/master/05-ServiceHystrix
[https_blog.csdn.net_forezp_article_details_81040990]: https://blog.csdn.net/forezp/article/details/81040990
[http_www.ityouknow.com_springcloud_2017_05_16_springcloud-hystrix.html]: http://www.ityouknow.com/springcloud/2017/05/16/springcloud-hystrix.html