微服务SpringCloud开弓之Hystrix熔断器「八」

官网资料

1、概述

• 分布式系统面临的问题

  分布式系统面临的问题
  复杂分布式体系结构中的应用程序 有数10个依赖关系,每个依赖关系在某些时候将不可避免地失败

• 服务雪崩
  多个微服务之间调用的时候，假设微服务A调用微服务B和微服务C,微服务B和微服务C又调用其它的微服务，这就是所谓的"扇出"。
  如果扇出的链路上某个微服务的调用响应时间过长或者不可用,对微服务A的调用就会占用越来越多的系统资源，进而引起系统崩溃，所谓的“雪崩效应”.

  对于高流量的应用来说，单-的后端依赖可能会导致所有服务器上的所有资源都在几秒钟内饱和。比失败更糟糕的是，这些应用程序还可能导致服务之间的延迟增加，备份队列，线程和其他系统资源紧张，导致整个系统发生更多的级联故障。这些都表示需要对故障和延迟进行隔离和管理，以便单个依赖关系的失败,不能取消整个应用程序或系统。

  所以,通常当你发现一个模块下的某个实例失败后,这时候这个模块依然还会接收流量,然后这个有问题的模块还调用了其他的模块,这样就会发生级联故障,或者叫雪崩。

• 是什么
  

• 作用

  服务降级

  服务熔断

  接近实时的监控

2、HyStrix重要概念

• 服务降级(fallback)

  1、 服务器忙,请稍后再试,不让客户端等待并立刻返回一个友好提示,fallback

  2、哪些情况会发出降级

  程序运行异常
  超时
  服务熔断触发服务降级
  线程池/信号量也会导致服务降级

• 服务熔断(break)

  类比保险丝达到最大服务访问后,直接拒绝访问,拉闸限电,然后调用服务降级的方法并返回友好提示

  就是保险丝 : 服务的降级->进而熔断->恢复调用链路

• 服务限流(flowlimit)

  秒杀高并发等操作,严禁一窝蜂的过来拥挤,大家排队,一秒钟N个,有序进行

3、hystrix案例

构建案例

1、新建cloud-provider-hystrix-payment8001

2、POM

  <!--hystrix-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
        </dependency>
        <!--eureka client-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <!--web-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <!--引入自定义的api通用包，可用使用Payment支付Entity-->
        <dependency>
            <groupId>com.atguigu.springcloud</groupId>
            <artifactId>cloud-api-common</artifactId>
            <version>${project.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

3、yml

server:
  port: 8001
spring:
  application:
    name: cloud-provider-hystrix-payment
eureka:
  client:
    register-with-eureka: true
    fetch-registry: true
    service-url:
      defaultZone: http://eureka7001.com:7001/eureka,http://eureka7002.com:7002/eureka

4、主启动类

@SpringBootApplication
@EnableEurekaClient
public class PaymentHystrixMain8001 {
    public static void main(String[] args) {
        SpringApplication.run(PaymentHystrixMain8001.class, args);
    }
}

5、业务类

• service

  @Service
  public class PaymentService {
      public String paymentInfo_OK(Integer id) {
          return "线程池:" + Thread.currentThread().getName() + " paymentInfo_OK,id:" + id + "\t" + "O(∩_∩)O哈哈~";
      }
  
      public String paymentInfo_TimeOut(Integer id) {
          int timeNumber = 3;
          try {
              // 暂停3秒钟
              TimeUnit.SECONDS.sleep(timeNumber);
          } catch (InterruptedException e) {
              e.printStackTrace();
          }
          return "线程池:" + Thread.currentThread().getName() + " paymentInfo_TimeOut,id:" + id + "\t" +
                  "O(∩_∩)O哈哈~  耗时(秒)" + timeNumber;
      }
  }
  

• controller

  @RestController
  @Slf4j
  public class PaymentController {
      @Resource
      private PaymentService paymentService;
  
      @Value("${server.port}")
      private String servicePort;
  
      @GetMapping("/payment/hystrix/ok/{id}")
      public String paymentInfo_OK(@PathVariable("id") Integer id) {
          String result = paymentService.paymentInfo_OK(id);
          log.info("*****result:" + result);
          return result;
      }
  
      @GetMapping("/payment/hystrix/timeout/{id}")
      public String paymentInfo_TimeOut(@PathVariable("id") Integer id) {
          String result = paymentService.paymentInfo_TimeOut(id);
          log.info("*****result:" + result);
          return result;
  
      }
  }
  

6、测试

正常的方法

• http://localhost:8001/payment/hystrix/ok/31

延时的方法

• http://localhost:8001/payment/hystrix/timeout/31

解决办法

ribbon:
  # 指的是建立连接所用的时间,适用于网络状态正常的情况下,两端连接所用的时间
  ReadTimeout: 5000
# 指的是建立连接后从服务器读取到可用资源所用的时间
  ConnectTimeout: 5000

高并发的测试：

开启Jmeter,来20000个并发压死8001,20000个请求都去访问paymentInfo_TimeOut服务

http://localhost:8001/payment/hystrix/timeout/31

http://localhost:8001/payment/hystrix/ok/31

都在转圈，没延迟的也受到了高并发的影响

原因：

tomcat的默认工作线程数被打满了,没有多余的线程来分解压力和处理

结论

上面还只是服务提供者8001自己测试,假如此时外部的消费者80也来访问,那消费者只能干等,最终导致消费端80不满意,服务端8001直接被拖死

80新建加入

1、新建cloud-consumer-feign-hystrix-order80

2、POM

    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
        </dependency>
        <!--openfeign-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <!--eureka client-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <dependency>
            <groupId>com.atguigu.springcloud</groupId>
            <artifactId>cloud-api-common</artifactId>
            <version>${project.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!--监控-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <!--热部署-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

3、YML

server:
  port: 80
eureka:
  client:
    register-with-eureka: false
    fetch-registry: true
    service-url:
      defaultZone: http://eureka7001.com:7001/eureka,http://eureka7002.com:7002/eureka

4、主启动

@SpringBootApplication
@EnableEurekaClient
@EnableHystrix
@EnableFeignClients
public class OrderHystrixMain80 {
    public static void main(String[] args) {
        SpringApplication.run(OrderHystrixMain80.class, args);
    }
}

5、业务类

• PaymentHystrixService

  @Component
  @FeignClient(value = "cloud-provider-hystrix-payment")
  public interface PaymentHystrixService {
  
      @GetMapping("/payment/hystrix/ok/{id}")
      String paymentInfo_OK(@PathVariable("id") Integer id);
  
  
  
      @GetMapping("/payment/hystrix/timeout/{id}")
      String paymentInfo_TimeOut(@PathVariable("id") Integer id);
  
  }
  
  

• OrderHysrixController

  @RestController
  @Slf4j
  public class OrderHysrixController {
  
      @Resource
      private PaymentHystrixService paymentHystrixService;
  
      @GetMapping(value ="/consumer/payment/hystrix/ok/{id}")
      public String paymentInfoOK(@PathVariable("id") Integer id){
          return paymentHystrixService.paymentInfo_OK(id);
      }
  
      @GetMapping(value ="/consumer/payment/hystrix/timeout/{id}")
      public String paymentInfo_TimeOut(@PathVariable("id") Integer id){
          return paymentHystrixService.paymentInfo_TimeOut(id);
      }
  

6、正常测试

http://localhost/consumer/payment/hystrix/ok/32 快速正常访问

7、高并发测试

• 消费者80微服务再去访问的OK服务8001地址

• 开启Jmeter,来20000个并发压死8001

• 访问http://localhost/consumer/payment/hystrix/ok/32

  结果：

  • 要么转圈圈

  • 要么报错

故障和导致现象

• 8001同一层次的其他接口被困死,因为tomcat线程池里面的工作线程已经被挤占完毕
• 80此时调用8001,客户端访问响应缓慢,转圈圈

上述结论

• 正因为有上述故障或不佳表现 才有我们的降级/容错/限流等技术诞生

如何解决?解决的要求

• 超时导致服务器变慢(转圈)

  超时不再等待

• 出错(宕机或程序运行出错)

  超时不再等待

• 解决

  1、对方服务(8001)超时了,调用者(80)不能一直卡死等待,必须有服务降级

  2、对方服务(8001)down机了,调用者(80)不能一直卡死等待,必须有服务降级

  3、对方服务(8001)ok,调用者(80)自己有故障或有自我要求(自己的等待时间小于服务提供者)

4、服务降级

降级配置

• @HystrixCommand

8001先从自身找问题

• 设置自身调用超时时间的峰值,峰值内可以正常运行, 超过了需要有兜底的方法处理,做服务降级fallback

8001fallback

• 业务类启用

  @HystrixCommand报异常后如何处理

  PaymentService

    @HystrixCommand(fallbackMethod = "paymentInfo_TimeOutHandler",commandProperties = {
              @HystrixProperty(name="execution.isolation.thread.timeoutInMilliseconds",value = "3000")
      })
      public String paymentInfo_TimeOut(Integer id) {
          int timeNumber = 5;
          try {
              // 暂停3秒钟
              TimeUnit.SECONDS.sleep(timeNumber);
          } catch (InterruptedException e) {
              e.printStackTrace();
          }
          return "线程池:" + Thread.currentThread().getName() + " paymentInfo_TimeOut,id:" + id + "\t" +
                  "O(∩_∩)O哈哈~  耗时(秒)" + timeNumber;
      }
  
      public String  paymentInfo_TimeOutHandler(Integer id){
          return "程序运行繁忙或报错,请稍后再试*****"+"当前线程: "+Thread.currentThread().getName()+id+"\t "+"orz!";
      }
  
  

  分析：

  一旦调用服务方法失败并抛出了错误信息后,会自动调用@HystrixCommand标注好的fallbckMethod调用类中的指定方法

• 主启动类激活

  @EnableCircuitBreaker

  @SpringBootApplication
  @EnableEurekaClient
  @EnableCircuitBreaker
  public class PaymentHystrixMain8001 {
      public static void main(String[] args) {
          SpringApplication.run(PaymentHystrixMain8001.class, args);
      }
  }
  

  结果：

  访问http://localhost:8001/payment/hystrix/timeout/31 超时走自定义回调函数
  

80fallback

我们自己配置过的热部署方式对java代码的改动明显,但对@HystrixCommand内属性的修改建议重启微服务

• pom

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

• yml

  server:
    port: 80
  eureka:
    client:
      register-with-eureka: false
      fetch-registry: true
      service-url:
        defaultZone: http://eureka7001.com:7001/eureka,http://eureka7002.com:7002/eureka
  feign:
    hystrix:
      enaled: true
  

• 主启动 @EnableHystrix

  @SpringBootApplication
  @EnableEurekaClient
  @EnableHystrix
  @EnableFeignClients
  public class OrderHystrixMain80 {
      public static void main(String[] args) {
          SpringApplication.run(OrderHystrixMain80.class, args);
      }
  }
  

• 业务类

  controller进行业务降级

  @RestController
  @Slf4j
  public class OrderHysrixController {
      @Resource
      private PaymentHystrixService paymentHystrixService;
  
      @GetMapping(value ="/consumer/payment/hystrix/ok/{id}")
      public String paymentInfoOK(@PathVariable("id") Integer id){
          return paymentHystrixService.paymentInfo_OK(id);
      }
  
      @GetMapping(value ="/consumer/payment/hystrix/timeout/{id}")  @HystrixCommand(fallbackMethod = "paymentTimeOutFallbackMethod",commandProperties = {         @HystrixProperty(name="execution.isolation.thread.timeoutInMilliseconds",value = "1500")   })
      @HystrixCommand
      public String paymentInfo_TimeOut(@PathVariable("id") Integer id){
          return paymentHystrixService.paymentInfo_TimeOut(id);
      }
  
      public  String  paymentTimeOutFallbackMethod(@PathVariable("id") Integer id){
          return "我是消费者80，对方支付系统繁忙"+"当前线程: "+Thread.currentThread().getName()+id+"\t "+"mgd!";
  
      }
  }
  

• 测试结果
  

存在的问题

• 每个业务方法对应一个兜底的方法,代码膨胀
• 统一和自定义的分开

解决办法

• 每个方法配置一个造成的冗余

  1、feign接口系列

  2、@DefaultProperties(defaultFallback="")

3、controller配置

@RestController
@Slf4j
@DefaultProperties(defaultFallback="paymentTimeOutFallbackMethod_Global")
public class OrderHysrixController {

    @Resource
    private PaymentHystrixService paymentHystrixService;

    @GetMapping(value ="/consumer/payment/hystrix/ok/{id}")
    public String paymentInfoOK(@PathVariable("id") Integer id){
        return paymentHystrixService.paymentInfo_OK(id);
    }

    @GetMapping(value ="/consumer/payment/hystrix/timeout/{id}")
    @HystrixCommand
    public String paymentInfo_TimeOut(@PathVariable("id") Integer id){
        return paymentHystrixService.paymentInfo_TimeOut(id);
    }

    public  String  paymentTimeOutFallbackMethod(@PathVariable("id") Integer id){
        return "我是消费者80，对方支付系统繁忙"+"当前线程: "+Thread.currentThread().getName()+id+"\t "+"mgd!";

    }

    public  String  paymentTimeOutFallbackMethod_Global(){
        return "我是全局异常"+"当前线程: "+Thread.currentThread().getName()+"\t "+"mgd!";

    }
}

• 和业务逻辑混在一起造成代码混乱

  服务降级,客户端去调用服务端,碰上服务端宕机或关闭

  本次案例服务降级处理是在客户端80实现完成,与服务端8001没有关系 只需要为Feign客户端定义的接口添加一个服务降级处理的实现类即可实现解耦

​ 1、修改cloud-consumer-feign-hystrix-order80

​ PaymentFeignClientService接口

@Component
@FeignClient(value = "cloud-provider-hystrix-payment" ,fallback = PaymentFallbackService.class)
public interface PaymentHystrixService {

 @GetMapping("/payment/hystrix/ok/{id}")
 String paymentInfo_OK(@PathVariable("id") Integer id);

 @GetMapping("/payment/hystrix/timeout/{id}")
 String paymentInfo_TimeOut(@PathVariable("id") Integer id);

}

2、根据cloud-consumer-feign-hystrix-order80已经有的PaymentHystrixService接口,重新新建一个类(PaymentFallbackService)实现接口,统一为接口里面的方法进行异常处理

3、PaymentFallbackService类实现PaymentFeginService接口

import org.springframework.stereotype.Component;

@Component
public class PaymentFallbackService implements PaymentHystrixService{
    @Override
    public String paymentInfo_OK(Integer id) {
        return "=========================PaymentFallbackService fall  back-paymentInfo_ok=======";
    }

    @Override
    public String paymentInfo_TimeOut(Integer id) {
        return "=========================PaymentFallbackService fall  back-paymentInfo_TimeOut=======";
    }
}

4、测试

正常访问http://localhost/consumer/payment/hystrix/ok/32

故意关闭微服务8001

结果如图所示

5、服务熔断

论文地址

说明

• 断路器

  一句话就是家里的保险丝

• 熔断是什么

实操

1、 修改cloud-provider-hystrix-payment8001

2、PaymentService

@HystrixCommand(fallbackMethod="paymentCircuitBreakerFallback", commandProperties={
            @HystrixProperty(name = "circuitBreaker.enabled" ,value = "true"),//是否开启断路器
            @HystrixProperty(name = "circuitBreaker.requestVolumeThreshold",value = "10"),// 请求次数
            @HystrixProperty(name = "circuitBreaker.sleepWindowInMilliseconds",value = "10000"),//时间窗口期 "
            @HystrixProperty(name = "circuitBreaker.errorThresholdPercentage",value = "60")//失败率达到多少后跳闸
            })
    public String paymentCircuitBreaker(@PathVariable("id") Integer id){
        if (id<0){
            throw new RuntimeException();
        }
        String serialNumber = IdUtil.simpleUUID();
        return Thread.currentThread().getName()+"\t "+"调用成功,流水号: "+serialNumber;
    }
    public String paymentCircuitBreakerFallback(@PathVariable("id") Integer id){
        return "id不能为负数,请稍后再试~ id: "+ id;
    }

3、PaymentController

    @GetMapping("/payment/circuit/{id}")
    public String paymentCircuitBreaker(@PathVariable("id") Integer id){
        String circuitBreaker = paymentService.paymentCircuitBreaker(id);
        log.info("******result: "+circuitBreaker);
        return circuitBreaker;
    }

结果

自测cloud-provider-hystrix-payment8001

http://localhost:8001/payment/circuit/31

http://localhost:8001/payment/circuit/-31

http://localhost:8001/payment/circuit/1

参数说明

源码：

public abstract class HystrixCommandProperties {
    private static final Logger logger = LoggerFactory.getLogger(HystrixCommandProperties.class);

    /* defaults */
    /* package */ static final Integer default_metricsRollingStatisticalWindow = 10000;// default => statisticalWindow: 10000 = 10 seconds (and default of 10 buckets so each bucket is 1 second)
    private static final Integer default_metricsRollingStatisticalWindowBuckets = 10;// default => statisticalWindowBuckets: 10 = 10 buckets in a 10 second window so each bucket is 1 second
    private static final Integer default_circuitBreakerRequestVolumeThreshold = 20;// default => statisticalWindowVolumeThreshold: 20 requests in 10 seconds must occur before statistics matter
    private static final Integer default_circuitBreakerSleepWindowInMilliseconds = 5000;// default => sleepWindow: 5000 = 5 seconds that we will sleep before trying again after tripping the circuit
    private static final Integer default_circuitBreakerErrorThresholdPercentage = 50;// default => errorThresholdPercentage = 50 = if 50%+ of requests in 10 seconds are failures or latent then we will trip the circuit
    private static final Boolean default_circuitBreakerForceOpen = false;// default => forceCircuitOpen = false (we want to allow traffic)
    /* package */ static final Boolean default_circuitBreakerForceClosed = false;// default => ignoreErrors = false 
    private static final Integer default_executionTimeoutInMilliseconds = 1000; // default => executionTimeoutInMilliseconds: 1000 = 1 second
    private static final Boolean default_executionTimeoutEnabled = true;
    private static final ExecutionIsolationStrategy default_executionIsolationStrategy = ExecutionIsolationStrategy.THREAD;
    private static final Boolean default_executionIsolationThreadInterruptOnTimeout = true;
    private static final Boolean default_executionIsolationThreadInterruptOnFutureCancel = false;
    private static final Boolean default_metricsRollingPercentileEnabled = true;
    private static final Boolean default_requestCacheEnabled = true;
    private static final Integer default_fallbackIsolationSemaphoreMaxConcurrentRequests = 10;
    private static final Boolean default_fallbackEnabled = true;
    private static final Integer default_executionIsolationSemaphoreMaxConcurrentRequests = 10;
    private static final Boolean default_requestLogEnabled = true;
    private static final Boolean default_circuitBreakerEnabled = true;
    private static final Integer default_metricsRollingPercentileWindow = 60000; // default to 1 minute for RollingPercentile 
    private static final Integer default_metricsRollingPercentileWindowBuckets = 6; // default to 6 buckets (10 seconds each in 60 second window)
    private static final Integer default_metricsRollingPercentileBucketSize = 100; // default to 100 values max per bucket
    private static final Integer default_metricsHealthSnapshotIntervalInMilliseconds = 500; // default to 500ms as max frequency between allowing snapshots of health (error percentage etc)
    @SuppressWarnings("unused") private final HystrixCommandKey key;
    private final HystrixProperty<Integer> circuitBreakerRequestVolumeThreshold; // number of requests that must be made within a statisticalWindow before open/close decisions are made using stats
    private final HystrixProperty<Integer> circuitBreakerSleepWindowInMilliseconds; // milliseconds after tripping circuit before allowing retry
    private final HystrixProperty<Boolean> circuitBreakerEnabled; // Whether circuit breaker should be enabled.
    private final HystrixProperty<Integer> circuitBreakerErrorThresholdPercentage; // % of 'marks' that must be failed to trip the circuit
    private final HystrixProperty<Boolean> circuitBreakerForceOpen; // a property to allow forcing the circuit open (stopping all requests)
    private final HystrixProperty<Boolean> circuitBreakerForceClosed; // a property to allow ignoring errors and therefore never trip 'open' (ie. allow all traffic through)
    private final HystrixProperty<ExecutionIsolationStrategy> executionIsolationStrategy; // Whether a command should be executed in a separate thread or not.
    private final HystrixProperty<Integer> executionTimeoutInMilliseconds; // Timeout value in milliseconds for a command
    private final HystrixProperty<Boolean> executionTimeoutEnabled; //Whether timeout should be triggered
    private final HystrixProperty<String> executionIsolationThreadPoolKeyOverride; // What thread-pool this command should run in (if running on a separate thread).
    private final HystrixProperty<Integer> executionIsolationSemaphoreMaxConcurrentRequests; // Number of permits for execution semaphore
    private final HystrixProperty<Integer> fallbackIsolationSemaphoreMaxConcurrentRequests; // Number of permits for fallback semaphore
    private final HystrixProperty<Boolean> fallbackEnabled; // Whether fallback should be attempted.
    private final HystrixProperty<Boolean> executionIsolationThreadInterruptOnTimeout; // Whether an underlying Future/Thread (when runInSeparateThread == true) should be interrupted after a timeout
    private final HystrixProperty<Boolean> executionIsolationThreadInterruptOnFutureCancel; // Whether canceling an underlying Future/Thread (when runInSeparateThread == true) should interrupt the execution thread
    private final HystrixProperty<Integer> metricsRollingStatisticalWindowInMilliseconds; // milliseconds back that will be tracked
    private final HystrixProperty<Integer> metricsRollingStatisticalWindowBuckets; // number of buckets in the statisticalWindow
    private final HystrixProperty<Boolean> metricsRollingPercentileEnabled; // Whether monitoring should be enabled (SLA and Tracers).
    private final HystrixProperty<Integer> metricsRollingPercentileWindowInMilliseconds; // number of milliseconds that will be tracked in RollingPercentile
    private final HystrixProperty<Integer> metricsRollingPercentileWindowBuckets; // number of buckets percentileWindow will be divided into
    private final HystrixProperty<Integer> metricsRollingPercentileBucketSize; // how many values will be stored in each percentileWindowBucket
    private final HystrixProperty<Integer> metricsHealthSnapshotIntervalInMilliseconds; // time between health snapshots
    private final HystrixProperty<Boolean> requestLogEnabled; // whether command request logging is enabled.
    private final HystrixProperty<Boolean> requestCacheEnabled; // Whether request caching is enabled.

涉汲到断路器的三个重要参数:快照时间窗、请求总数阀值、错误百分比阀值**。

• 1、快照时间窗:断路器确定是否打开需要统计一些请求和错误数据，而统计的时间范围就是快照时间窗,默认为最近的10秒。
• 2、请求总数阀值:在快照时间窗内，必须满足请求总数阀值才有资格熔断。默认为20, 意味着在10秒内,如果该hystrix命令的调用次数不足20次,即使所有的请求都超时或其他原因失败，断路器都不会打开。
• 3、错误百分比阀值:当请求总、在快照时间窗内超过了阀值，比如发生了30次调用，如果在这30次调用中，有15次发生了超时异常,也就是超过50%的错误百分比，在默认设定50%阀值情况下，这时候就会将断路器打开。

原来的主逻辑要如何恢复呢?

对于这一-问题，hystrix也为我们实现了自动恢复功能。

• 当断路器打开,对主逻辑进行熔断之后，hystrix会启动一个休眠时间窗在这个时间窗内,降级逻辑是临时的成为主逻辑，
• 当休眠时间窗到期，断路器将进入半开状态,释放一次请求到原来的主逻辑上,如果此次请求正常返回,那么断路器将继续闭合,
• 主逻辑恢复,如果这次请求依然有问题，断路器继续进入打开状态,休眠时间窗重新计时。

原理/小总结

官网原理图

1、官网步骤

2、断路器开启或者关闭的条件

• 当满足一定的阈值的时候(默认10秒钟超过20个请求次数)
• 当失败率达到一定的时候(默认10秒内超过50%的请求次数)
• 到达以上阈值,断路器将会开启
• 当开启的时候,所有请求都不会进行转发
• 一段时间之后(默认5秒),这个时候断路器是半开状态,会让其他一个请求进行转发. 如果成功,断路器会关闭,若失败,继续开启.重复4和5

6、服务限流

后面高级篇讲解alibaba的Sentinel说明

7、hystrix工作流程

官网地址

图例

步骤说明

8、服务监控hystrixDashboard

• 概述

• 仪表盘9001搭建

  1、新建cloud-consumer-hystrix-dashboard9001

  2、POM

    <dependencies>
          <!--hystrix dashboard-->
          <dependency>
              <groupId>org.springframework.cloud</groupId>
              <artifactId>spring-cloud-starter-netflix-hystrix-dashboard</artifactId>
          </dependency>
          <!--监控-->
          <dependency>
              <groupId>org.springframework.boot</groupId>
              <artifactId>spring-boot-starter-actuator</artifactId>
          </dependency>
          <!--热部署-->
          <dependency>
              <groupId>org.springframework.boot</groupId>
              <artifactId>spring-boot-devtools</artifactId>
              <scope>runtime</scope>
              <optional>true</optional>
          </dependency>
          <dependency>
              <groupId>org.projectlombok</groupId>
              <artifactId>lombok</artifactId>
              <optional>true</optional>
          </dependency>
          <dependency>
              <groupId>org.springframework.boot</groupId>
              <artifactId>spring-boot-starter-test</artifactId>
              <scope>test</scope>
          </dependency>
      </dependencies>
  

  3、YML

  server:
    port: 9001
  

  4、HystrixDashboardMain9001+新注解@EnableHystrixDashboard

  @SpringBootApplication
  @EnableHystrixDashboard
  public class HystrixDashboardMain9001 {
      public static void main(String[] args) {
          SpringApplication.run(HystrixDashboardMain9001.class,args);
      }
  }
  

  5、测试

启动一个eureka或者3个eureka集群均可

• 9001监控8001

  填写监控地址：http://localhost:8001/hystrix.stream

• 测试地址

  http://localhost:8001/payment/circuit/31

  http://localhost:8001/payment/circuit/-31

  先访问正确地址,再访问错误地址,再正确地址,会发现图标断路器都是慢慢放开的.

• 监控结果,成功

• 测试结果，失败

6、如何看?

• 七色
  

• 一圈

  实心圆:共有两种含义。它通过颜色的变化代表了实例的健康程度,它的健康度从绿色<黄色<橙色<红色递减。

  该实心圆除了颜色的变化之外,它的大小也会根据实例的请求流量发生变化,流量越大该实心圆就越大。所以通过该实心圆的展示，就可以在大量的实例中快速的发现故障实例和高压力实例。

• 一线

  一条曲线可以观察到流量的上升与下降的趋势

图片参数说明

最终搞懂的集群图例