使用Hystrix实现微服务的容错处理

使用Hystrix实现微服务的容错处理

微服务

容错处理

Hystrix

一、实现容错的手段

如果服务提供者响应非常缓慢，那么消费者对提供者的请求就会被强制等待，直到提供者响应或超时。在高负荷的场景下，如果不作任何处理，此类可能导致服务消费者的资源耗尽，甚至整个系统的崩溃。

如图：A作为服务提供者（基础服务），B为A的服务消费者，C和D是B的服务消费者，当A不可用引起不了B的不可用，并将不可用像滚雪球一样放大到C和D时，雪崩效应就形成了：

二、使用Hystrix实现容错

Hystrix是由Netfilx开源的一个延迟和容错库，用于隔离访问远程系统、服务或者第三方放库，防止级联失败，从而提升系统的可用性和容错性。

三、通用方式整合Hystrix

1. 复制项目microservice-consumer-movie-ribbon，将ArtifacId修改为microservice-comsumer-movie-ribbon-hystrix

2. 为项目添加以下依赖

<!--Hystrix依赖-->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-hystrix</artifactId>
</dependency>

3. 在启动类上添加注解@EnableCircuitBreaker或@EnableHystrix

@SpringBootApplication
@EnableEurekaServer
@EnableHystrix
public class ConsumerMovieApplication {
@Bean
@LoadBalanced
public RestTemplate restTemplate(){
return new RestTemplate();
}
public static void main(String[] args) {
SpringApplication.run(ConsumerMovieApplication.class, args);
}
}

4. 修改MovieController

@RestController
public class MovieController {
private static final Logger LOGGER = LoggerFactory.getLogger(MovieController.class);
@Autowired
private RestTemplate restTemplate;
@Autowired
private LoadBalancerClient loadBalancerClient;

@HystrixCommand(fallbackMethod = "findByIdFallback") //为findById方法指定出错回退的方法

@GetMapping("/user/{id}")
public User findById(@PathVariable Long id) {
return this.restTemplate.getForObject("http://microservice-provider-user/" + id, User.class);
}
public User findByIdFallback(Long id){
User user = new User();
user.setId(45L);
user.setName("默认用户");
return user;
}

}

5. 测试

启动项目：microservice-discover-eureka

启动项目：microservice-provider-user

启动项目：microservice-consumer-movie-ribbon-hystrix

访问http://localhost:8010/user/1，获得以下结果

<User>
<id>1</id>
<username/>
<name>hyh</name>
<age>12</age>
<balance/>
</User>

停止 microservice-provider-user

再次访问http://localhost:8010/user/1，获得如下结果

<User>
<id>45</id>
<username/>
<name>默认用户</name>
<age/>
<balance/>
</User>

当用户微服务不可用时，进入倒退方法！

四、Hystrix断路器的状态监控与深入理解

{"description":"Composite Discovery Client","status":"UP"}

<User>
<id>45</id>
<username/>
<name>默认用户</name>
<age/>
<balance/>
</User>

Hystrix线程隔离策略与传播上下文

五、Feign使用Hystrix

———-为Feign添加回退 ———–

1. 复制项目microservice-comsumer-movie-feign，将ArtifactId修改为microservice-consumer-movie-feign-hystrix-fallback

2. 将之前编写的Feign接口修改为如下内容：

/**
* Feign的fallback测试
* 使用@FeignClient的fallback属性指定回退类
*
*/
@FeignClient(name = "microservice-provider-user", fallback = FeignClientFallback.class)
public interface UserFeignClient {
@RequestMapping(value = "/{id}", method = RequestMethod.GET)
public User findById(@PathVariable("id") Long id);
}
@Component
class FeignClientFallback implements UserFeignClient {
@Override
public com.itmuch.cloud.study.user.entity.User findById(Long id) {
com.itmuch.cloud.study.user.entity.User user = new com.itmuch.cloud.study.user.entity.User();
user.setId(-1L);
user.setUsername("默认用户");
return user;
}
}

由代码可以看出，只许使用@FeignClient注解fallback属性，就可以指定名称的Feign客户端添加回退

3. application.yml文件添加

feign:
hystrix:
enabled: true

4. 测试

使用上面的测试流程即可，结果同上，自己分析

———-通过Fallback Factory 检查回退原因———

1. 复制项目microservice-comsumer-movie-feign,将ArtfactId修改为microservice-consumer-movie-feifn-hystrix-fallback-factory

2.将UserFeignClient改为如下内容

@FeignClient(name = "microservice-provider-user",fallbackFactory = FeignClientFallbackFactory.class)
public interface UserFeignClient {
@RequestMapping(value = "/{id}", method = RequestMethod.GET)
public User findById(@PathVariable("id") Long id);
}

@Component
class FeignClientFallbackFactory implements FallbackFactory<UserFeignClient> {
private static final Logger LOGGER = LoggerFactory.getLogger(FeignClientFallbackFactory.class);
@Override
public UserFeignClient create(Throwable cause) {
return new UserFeignClient() {
@Override
public User findById(Long id) {
FeignClientFallbackFactory.LOGGER.info("fallback; reason was",cause);
User user = new User();
user.setId(-1L);
user.setUsername("默认用户");
return user;
}
};
}
}

当Feign发生回退时，就会打印日志

3. 测试

启动项目：microservice-discover-eureka

启动项目：microservice-provider-user

启动项目：microservice-consumer-movie-ribbon-hystrix

访问http://localhost:8010/user/1，获得以下结果

<User>
<id>1</id>
<username/>
<name>hyh</name>
<age>12</age>
<balance/>
</User>

停止 microservice-provider-user

再次访问http://localhost:8010/user/1，获得如下结果

<User>
<id>45</id>
<username/>
<name>默认用户</name>
<age/>
<balance/>
</User>

当用户微服务不可用时，进入倒退方法！

四、Hystrix断路器的状态监控与深入理解

{"description":"Composite Discovery Client","status":"UP"}

<User>
<id>45</id>
<username/>
<name>默认用户</name>
<age/>
<balance/>
</User>

五、Hystrix监控

除实现容错，Hystrix还提供了近乎实时监控，使用Hystrix的模块hystrix-metrice-event-strem，就可以将这些监控的指标信息以/text/event-stream的格式暴露给外部系统，只须为项目添加spring-boot-starter-actuator,就可以使用/hystirix.stream端点获得Hystrix的监控信息了

测试

启动：microservice-discovery-eureka

启动：microservice-provider-user

启动：microservice-consumer-movie-ribbon-hystrix

访问：http://localhost:8010/hystrix.stream，可看到浏览器一直处于请求状态，页面空白，这是此时项目注解@HystrixCommand的方法换没有被执行，因此没有任何监控

访问：http://localhost:8010/user/1,再次访问http://localhost:8010/hystirx.stream,可看懂页面会出现类似下面的内容

ping:

data: {"type":"HystrixCommand","name":"findById","group":"MovieController","currentTime":1516324378672,"isCircuitBreakerOpen":false,"errorPercentage":0,"errorCount":0,"requestCount":1,"rollingCountBadRequests":0,"rollingCountCollapsedRequests":0,"rollingCountEmit":0,"rollingCountExceptionsThrown":0,"rollingCountFailure":0,"rollingCountFallbackEmit":0,"rollingCountFallbackFailure":0,"rollingCountFallbackMissing":0,"rollingCountFallbackRejection":0,"rollingCountFallbackSuccess":0,"rollingCountResponsesFromCache":0,"rollingCountSemaphoreRejected":0,"rollingCountShortCircuited":0,"rollingCountSuccess":1,"rollingCountThreadPoolRejected":0,"rollingCountTimeout":0,"currentConcurrentExecutionCount":0,"rollingMaxConcurrentExecutionCount":0,"latencyExecute_mean":0,"latencyExecute":{"0":0,"25":0,"50":0,"75":0,"90":0,"95":0,"99":0,"99.5":0,"100":0},"latencyTotal_mean":0,"latencyTotal":{"0":0,"25":0,"50":0,"75":0,"90":0,"95":0,"99":0,"99.5":0,"100":0},"propertyValue_circuitBreakerRequestVolumeThreshold":20,"propertyValue_circuitBreakerSleepWindowInMilliseconds":5000,"propertyValue_circuitBreakerErrorThresholdPercentage":50,"propertyValue_circuitBreakerForceOpen":false,"propertyValue_circuitBreakerForceClosed":false,"propertyValue_circuitBreakerEnabled":true,"propertyValue_executionIsolationStrategy":"THREAD","propertyValue_executionIsolationThreadTimeoutInMilliseconds":1000,"propertyValue_executionTimeoutInMilliseconds":1000,"propertyValue_executionIsolationThreadInterruptOnTimeout":true,"propertyValue_executionIsolationThreadPoolKeyOverride":null,"propertyValue_executionIsolationSemaphoreMaxConcurrentRequests":10,"propertyValue_fallbackIsolationSemaphoreMaxConcurrentRequests":10,"propertyValue_metricsRollingStatisticalWindowInMilliseconds":10000,"propertyValue_requestCacheEnabled":true,"propertyValue_requestLogEnabled":true,"reportingHosts":1,"threadPool":"MovieController"}

上面就是Hystrix的监控，Hystrix的监控指标非常全面，例如HystrixCommand的名称、group名称、断路器状态、错误率、错误数等

使用Hystrix Dashboard

上面返回的监控信息是以文字展示的，很难通过这些数据，一眼看出系统的当前系统的运行状态。下面我们来使用Hystrix Dashboard，让监控数据图形化、可视化。更加的易于查看！

下面来编写一个Hystri
b509
x Dashboard

1. 创建一个Maven项目，ArtifactId是一个microservice-hystrix-dashboard，并为项目添加依赖

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

2. 编写启动类，在启动类上添加@EnableHystrixDashboard

@SpringBootApplication
@EnableHystrixDashboard
public class ProviderUserApplication {

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

3. 在配置文件application.yml中添加如下内容

server:
port: 8030

这样简单的Hystrix Dashboard就完成了。

4. 测试

访问http://localhost:8010/hystrix.stream，就可以看到Hystrix Dashboard主页



在上节测试的基础上，在URL栏中输入http://localhost:8010/hystrix.stream，然后点击Monitor Stream按钮后，即可看到类似界面



期间我犯了一错误，地址打错了，就会出现这个问题：

Unable to connect to Command Metric Stream.

正确的地址

http://localhost:8010/hystrix.stream