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。
