hystrix的使用

2018-08-30 本文已影响0人 braveheart075

hystrix

A service failure in the lower level of services can cause cascading failure all the way up to the user. 
When calls to a particular service is greater than circuitBreaker.requestVolumeThreshold (default: 20 requests) and failue percentage is greater than circuitBreaker.errorThresholdPercentage (default: >50%) in a rolling window defined by metrics.rollingStats.timeInMilliseconds (default: 10 seconds), 
the circuit opens and the call is not made. In cases of error and an open circuit a fallback can be provided by the developer.

How to Include Hystrix
- To include Hystrix in your project use the starter with group org.springframework.cloud and artifact id spring-cloud-starter-hystrix
- you can see here for more deatils.

Default fallback method should not have any parameters except extra one to get execution exception and shouldn't throw any exceptions. Below fallbacks listed in descending order of priority:
- command fallback defined using fallbackMethod property of @HystrixCommand
- command default fallback defined using defaultFallback property of @HystrixCommand
- class default fallback defined using defaultFallback property of @DefaultProperties
对于hystrix究竟是使用thread和semaphore，官网解释如下：
- thread:请求是在一个单独的线程中执行，当前请求受限与线程池中线程的数量
- semaphore：请求在当前线程执行，但是当前请求数受限于信号量计数大小。
对于使用线程池的，有一层额外的保护防止网络超时。所以需要配置超时的，可以采用线程池的方式。
在你的请求量很大，通常情况下达到每秒上百甚至更多的情况下，单个线程的请求量已经过高，此种情况才使用信号量。这种典型仅仅应用于非网络请求。

hystrix断路器说明
我们看下目前代码中的配置：

@HystrixCommand(commandProperties = {
      @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "5000"),
      @HystrixProperty(name = "circuitBreaker.requestVolumeThreshold",value = "5"),
      @HystrixProperty(name = "circuitBreaker.sleepWindowInMilliseconds",value = "5000000"),
      @HystrixProperty(name = "circuitBreaker.errorThresholdPercentage",value = "10"),
      @HystrixProperty(name = "circuitBreaker.forceOpen",value = "false"),
      @HystrixProperty(name = "fallback.enabled",value = "true")
  },
      threadPoolProperties = {
          @HystrixProperty(name = "coreSize", value = "30"),
          @HystrixProperty(name = "maxQueueSize", value = "101"),
          @HystrixProperty(name = "keepAliveTimeMinutes", value = "2"),
          @HystrixProperty(name = "queueSizeRejectionThreshold", value = "15"),
          @HystrixProperty(name = "metrics.rollingStats.numBuckets", value = "10"),
          @HystrixProperty(name = "metrics.rollingStats.timeInMilliseconds", value = "10000")
      })
  public String hystrixTest() {
      log.info("into service......");
      test();
      return "hystrix";
  }

requestVolumeThreshold = 5,这里配置的是5，也就说时间窗口内最小的请求数达到5，如果是4，哪怕4个请求全部有问题，都不会出发断路器打开。有一点你要注意，你这里配置了fallback,且默认都fallback是开启的，在异常捕获的时候，也没有忽略任何异常，所以每次请求都会进入fallback方法，service方法也会进去。断路器没有打开。
当你超过了5个请求，这个时候，你可以看到断路器开启了。此时fallback方法调用了，但是你进入不了service方法。sleepWindowInMilliseconds这个参数，如果设置了永久，那么你的断路器永远不会关闭。

我们来测试下，超过5个请求后，percentage生效的情况。在第6池开始抛异常，我们看下日志：

2018-08-30 15:35:21.079  INFO 47508 --- [nio-8086-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet 'dispatcherServlet': initialization completed in 18 ms
2018-08-30 15:35:21.103  INFO 47508 --- [nio-8086-exec-1] com.brave.web.Demo                       : into controller...
2018-08-30 15:35:21.318  INFO 47508 --- [x-DemoService-1] com.brave.service.DemoService            : into service......
2018-08-30 15:35:21.318  INFO 47508 --- [x-DemoService-1] com.brave.service.DemoService            : into test method,not throw exception...
2018-08-30 15:35:22.242  INFO 47508 --- [trap-executor-0] c.n.d.s.r.aws.ConfigClusterResolver      : Resolving eureka endpoints via configuration
2018-08-30 15:35:22.295  INFO 47508 --- [nio-8086-exec-3] com.brave.web.Demo                       : into controller...
2018-08-30 15:35:22.297  INFO 47508 --- [x-DemoService-2] com.brave.service.DemoService            : into service......
2018-08-30 15:35:22.297  INFO 47508 --- [x-DemoService-2] com.brave.service.DemoService            : into test method,not throw exception...
2018-08-30 15:35:23.184  INFO 47508 --- [nio-8086-exec-4] com.brave.web.Demo                       : into controller...
2018-08-30 15:35:23.186  INFO 47508 --- [x-DemoService-3] com.brave.service.DemoService            : into service......
2018-08-30 15:35:23.186  INFO 47508 --- [x-DemoService-3] com.brave.service.DemoService            : into test method,not throw exception...
2018-08-30 15:35:24.048  INFO 47508 --- [nio-8086-exec-5] com.brave.web.Demo                       : into controller...
2018-08-30 15:35:24.049  INFO 47508 --- [x-DemoService-4] com.brave.service.DemoService            : into service......
2018-08-30 15:35:24.049  INFO 47508 --- [x-DemoService-4] com.brave.service.DemoService            : into test method,not throw exception...
2018-08-30 15:35:24.863  INFO 47508 --- [nio-8086-exec-6] com.brave.web.Demo                       : into controller...
2018-08-30 15:35:24.865  INFO 47508 --- [x-DemoService-5] com.brave.service.DemoService            : into service......
2018-08-30 15:35:24.865  INFO 47508 --- [x-DemoService-5] com.brave.service.DemoService            : into test method,not throw exception...
2018-08-30 15:35:26.328  INFO 47508 --- [nio-8086-exec-7] com.brave.web.Demo                       : into controller...
2018-08-30 15:35:26.329  INFO 47508 --- [x-DemoService-6] com.brave.service.DemoService            : into service......
2018-08-30 15:35:26.329  INFO 47508 --- [x-DemoService-6] com.brave.service.DemoService            : into test method,not throw exception...
2018-08-30 15:35:26.329  INFO 47508 --- [x-DemoService-6] com.brave.service.DemoService            : throw an exception....
2018-08-30 15:35:27.787  INFO 47508 --- [nio-8086-exec-8] com.brave.web.Demo                       : into controller...
2018-08-30 15:35:29.945  INFO 47508 --- [nio-8086-exec-9] com.brave.web.Demo                       : into controller...
2018-08-30 15:35:32.246  INFO 47508 --- [trap-executor-0] c.n.d.s.r.aws.ConfigClusterResolver      : Resolving eureka endpoints via configuration
2018-08-30 15:35:34.064  INFO 47508 --- [io-8086-exec-10] com.brave.web.Demo                       : into controller...
2018-08-30 15:35:35.770  INFO 47508 --- [nio-8086-exec-2] com.brave.web.Demo                       : into controller...
2018-08-30 15:35:36.971  INFO 47508 --- [nio-8086-exec-1] com.brave.web.Demo                       : into controller...

我们可以看到，在第6哥请求的时候抛了一个异常。第7个请求无法进入，因为断路器开启了。我们设置第percentage是10%。符合预期。如果把这个值放大，会是什么结果？继续看下：

@Service
@DefaultProperties(defaultFallback = "fallback")
@Slf4j
public class DemoService {

    @Autowired DemoClient demoClient;

    public static AtomicInteger number = new AtomicInteger(0);

    public Optional<String> demo() {
        return Optional.ofNullable(demoClient.callDemo());
    }

    @HystrixCommand(commandProperties = {
        @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "5000"),
        @HystrixProperty(name = "circuitBreaker.requestVolumeThreshold",value = "5"),
        @HystrixProperty(name = "circuitBreaker.sleepWindowInMilliseconds",value = "5000000"),
        @HystrixProperty(name = "circuitBreaker.errorThresholdPercentage",value = "50"),
        @HystrixProperty(name = "circuitBreaker.forceOpen",value = "false"),
        @HystrixProperty(name = "fallback.enabled",value = "true")
    },
        threadPoolProperties = {
            @HystrixProperty(name = "coreSize", value = "30"),
            @HystrixProperty(name = "maxQueueSize", value = "101"),
            @HystrixProperty(name = "keepAliveTimeMinutes", value = "2"),
            @HystrixProperty(name = "queueSizeRejectionThreshold", value = "15"),
            @HystrixProperty(name = "metrics.rollingStats.numBuckets", value = "10"),
            @HystrixProperty(name = "metrics.rollingStats.timeInMilliseconds", value = "10000")
        })
    public String hystrixTest() {
        log.info("into service......");
        test();
        return "hystrix";
    }

    public String fallback() {
        return "fallback";
    }

    public void test() {
        int num = number.addAndGet(1);
        log.info("into test method,not throw exception...");
        if(num>5) {
            log.info("throw an exception....");
            throw new NullPointerException();
        }
    }

}

这里，把percentage调整到了50，我们看下日志：

2018-08-30 15:39:30.690  INFO 47514 --- [nio-8086-exec-1] com.brave.web.Demo                       : into controller...
2018-08-30 15:39:30.892  INFO 47514 --- [x-DemoService-1] com.brave.service.DemoService            : into service......
2018-08-30 15:39:30.892  INFO 47514 --- [x-DemoService-1] com.brave.service.DemoService            : into test method,not throw exception...
2018-08-30 15:39:31.235  INFO 47514 --- [nio-8086-exec-3] com.brave.web.Demo                       : into controller...
2018-08-30 15:39:31.237  INFO 47514 --- [x-DemoService-2] com.brave.service.DemoService            : into service......
2018-08-30 15:39:31.237  INFO 47514 --- [x-DemoService-2] com.brave.service.DemoService            : into test method,not throw exception...
2018-08-30 15:39:31.969  INFO 47514 --- [nio-8086-exec-4] com.brave.web.Demo                       : into controller...
2018-08-30 15:39:31.971  INFO 47514 --- [x-DemoService-3] com.brave.service.DemoService            : into service......
2018-08-30 15:39:31.971  INFO 47514 --- [x-DemoService-3] com.brave.service.DemoService            : into test method,not throw exception...
2018-08-30 15:39:32.507  INFO 47514 --- [trap-executor-0] c.n.d.s.r.aws.ConfigClusterResolver      : Resolving eureka endpoints via configuration
2018-08-30 15:39:32.849  INFO 47514 --- [nio-8086-exec-5] com.brave.web.Demo                       : into controller...
2018-08-30 15:39:32.851  INFO 47514 --- [x-DemoService-4] com.brave.service.DemoService            : into service......
2018-08-30 15:39:32.851  INFO 47514 --- [x-DemoService-4] com.brave.service.DemoService            : into test method,not throw exception...
2018-08-30 15:39:33.947  INFO 47514 --- [nio-8086-exec-6] com.brave.web.Demo                       : into controller...
2018-08-30 15:39:33.949  INFO 47514 --- [x-DemoService-5] com.brave.service.DemoService            : into service......
2018-08-30 15:39:33.949  INFO 47514 --- [x-DemoService-5] com.brave.service.DemoService            : into test method,not throw exception...
2018-08-30 15:39:35.329  INFO 47514 --- [nio-8086-exec-7] com.brave.web.Demo                       : into controller...
2018-08-30 15:39:35.330  INFO 47514 --- [x-DemoService-6] com.brave.service.DemoService            : into service......
2018-08-30 15:39:35.331  INFO 47514 --- [x-DemoService-6] com.brave.service.DemoService            : into test method,not throw exception...
2018-08-30 15:39:35.331  INFO 47514 --- [x-DemoService-6] com.brave.service.DemoService            : throw an exception....
2018-08-30 15:39:37.292  INFO 47514 --- [nio-8086-exec-8] com.brave.web.Demo                       : into controller...
2018-08-30 15:39:37.293  INFO 47514 --- [x-DemoService-7] com.brave.service.DemoService            : into service......
2018-08-30 15:39:37.293  INFO 47514 --- [x-DemoService-7] com.brave.service.DemoService            : into test method,not throw exception...
2018-08-30 15:39:37.293  INFO 47514 --- [x-DemoService-7] com.brave.service.DemoService            : throw an exception....
2018-08-30 15:39:40.416  INFO 47514 --- [nio-8086-exec-9] com.brave.web.Demo                       : into controller...
2018-08-30 15:39:40.417  INFO 47514 --- [x-DemoService-8] com.brave.service.DemoService            : into service......
2018-08-30 15:39:40.418  INFO 47514 --- [x-DemoService-8] com.brave.service.DemoService            : into test method,not throw exception...
2018-08-30 15:39:40.418  INFO 47514 --- [x-DemoService-8] com.brave.service.DemoService            : throw an exception....
2018-08-30 15:39:41.848  INFO 47514 --- [io-8086-exec-10] com.brave.web.Demo                       : into controller...
2018-08-30 15:39:42.512  INFO 47514 --- [trap-executor-0] c.n.d.s.r.aws.ConfigClusterResolver      : Resolving eureka endpoints via configuration
2018-08-30 15:39:47.632  INFO 47514 --- [nio-8086-exec-2] com.brave.web.Demo                       : into controller...
2018-08-30 15:39:48.811  INFO 47514 --- [nio-8086-exec-1] com.brave.web.Demo                       : into controller...

我们看到从第六次开始抛异常，一直到第9次，然后就没有第10次了。>=50%了，断路器打开了。符合预期。
以上大家可以参照我测试第过程，便于大家更清楚的知道断路器的原理。至于scrollwindow和bucket，大家继续再按此方法测试吧，本地模拟不太方便。

我们继续来看下execution.isolation.thread.timeoutInMilliseconds这个参数，我这里设置成5000，也就是说该方法5秒超时，在方法里,sleep了6秒，执行结果看下

2018-08-30 15:53:22.137  INFO 47619 --- [nio-8086-exec-2] com.brave.web.Demo                       : into controller...
2018-08-30 15:53:27.337  INFO 47619 --- [x-DemoService-1] com.brave.service.DemoService            : into service......
2018-08-30 15:53:27.337  INFO 47619 --- [x-DemoService-1] com.brave.service.DemoService            : into test method,not throw exception...
2018-08-30 15:53:27.347  INFO 47619 --- [ HystrixTimer-1] com.brave.service.DemoService            : into fallback....

方法超时6秒，过了6秒继续执行，由于超时了，fallback也执行了。

网上很多杂七杂八的说明，其实都是翻译的官网，很多人看了一知半解，希望这个对大家了解参数有帮助。

hystrix的使用

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