Hystrix使用分析

Hystrix使用

使用Hystrix实现熔断

要实现熔断，首先需要在请求调用方pom文件中加入

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

在启动类上加入@EnableCircuitBreaker注解，并在调用到另一个微服务的方法上加入一些配置

 @GetMapping("/checkHystrix/{userId}")@HystrixCommand(threadPoolKey = "checkHystrix1",threadPoolProperties = {@HystrixProperty(name = "coreSize",value = "1"),@HystrixProperty(name = "maxQueueSize",value = "20")},commandProperties = {@HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds",value="2000")})public Integer checkHystrix(@PathVariable Long userId) {String url = "http://zhao-service-resume/resume/openstate/"+userId;Integer forObject =restTemplate.getForObject(url, Integer.class);return forObject;}

将调用到的服务中加入线程休眠十秒。访问上述服务，在界面上即可发现Hystrix的超时错误

服务降级

在配置中再增加一个 fallbackMethod = "customeFallback"，配置降级兜底方法的具体形式是

    public  Integer customeFallback(Long userId){return -1;}

当某个服务熔断之后，服务器将不再被调⽤，此刻客户端可以⾃⼰准备⼀个本地的fallback回调，返回⼀个缺省值，这样做，虽然服务⽔平下降，但好⽍可⽤，⽐直接挂掉要强。但是在配置服务降级策略时，降级（兜底）⽅法必须和被降级⽅法相同的⽅法签名（相同参数列表、相同返回值）如果参数不同会出现com.netflix.hystrix.contrib.javanica.exception.FallbackDefinitionException: fallback method wasn't found: customeFallback([class java.lang.Long]) 如果返回值不同会出现。且包装类和基本类型不能共用 Hint: Fallback method 'public int com.zp.controller.AutoDeliverController.customeFallback(java.lang.Long)' must return: class java.lang.Integer or its subclass

仓壁模式(线程池隔离模式)

如果不进⾏任何线程池设置，所有熔断⽅法使⽤⼀个Hystrix线程池（默认为10个线程），那么这样的话会导致问题，这个问题并不是扇出链路微服务不可⽤导致的，⽽是我们的线程机制导致的，如果⽅法A的请求把10个线程都⽤了，⽅法2请求处理的时候压根都、没法去访问B，因为没有线程可⽤，并不是B服务不可⽤。因此在配置Hystrix线程时，多个方法应该写多个线程池。这样能够让线程之间互不影响

  @GetMapping("/checkHystrix/{userId}")@HystrixCommand(threadPoolKey = "checkHystrix1",threadPoolProperties = {@HystrixProperty(name = "coreSize",value = "1"),@HystrixProperty(name = "maxQueueSize",value = "20")},commandProperties = {@HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds",value="2000")})public Integer checkHystrix(@PathVariable Long userId) {String url = "http://zhao-service-resume/resume/openstate/"+userId;Integer forObject =restTemplate.getForObject(url, Integer.class);return forObject;}@GetMapping("/checkHystrixFallback/{userId}")@HystrixCommand(threadPoolKey = "checkHystrix2",threadPoolProperties = {@HystrixProperty(name = "coreSize",value = "2"),@HystrixProperty(name = "maxQueueSize",value = "20")},commandProperties = {@HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds",value="2000")},fallbackMethod = "customeFallback")

通过postman发送批量请求，并通过jstack命令可以看到两个方法的线程池进行了隔离

其他属性的含义

            commandProperties = {@HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds",value="2000"),@HystrixProperty(name = "metrics.rollingStats.timeInMilliseconds",value = "8000"),@HystrixProperty(name = "circuitBreaker.requestVolumeThreshold",value = "2"),@HystrixProperty(name = "circuitBreaker.errorThresholdPercentage",value="50"),@HystrixProperty(name = "circuitBreaker.sleepWindowInMilliseconds",value="3000")}

metrics.rollingStats.timeInMilliseconds该属性是下面的熔断的统计时间窗口定义 circuitBreaker.requestVolumeThreshold该属性统计时间窗⼝内的失败的次数，达到此次数之后开启熔断操作 circuitBreaker.errorThresholdPercentage 窗口内失败的次数的百分比，达到这个百分比之后开启熔断操作 circuitBreaker.sleepWindowInMilliseconds 熔断多久间隔多久以后开始尝试是否恢复

源码简要分析

首先我们根据注解类@EnableCircuitBreaker可以找到SpringFactoryImportSelector类，该类通过泛型在spring.factories文件中找到注解了该泛型的配置类

@Overridepublic String[] selectImports(AnnotationMetadata metadata) {if (!isEnabled()) {return new String[0];}AnnotationAttributes attributes = AnnotationAttributes.fromMap(metadata.getAnnotationAttributes(this.annotationClass.getName(), true));Assert.notNull(attributes, "No " + getSimpleName() + " attributes found. Is "+ metadata.getClassName() + " annotated with @" + getSimpleName() + "?");// Find all possible auto configuration classes, filtering duplicatesList<String> factories = new ArrayList<>(new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(this.annotationClass, this.beanClassLoader)));if (factories.isEmpty() && !hasDefaultFactory()) {throw new IllegalStateException("Annotation @" + getSimpleName()+ " found, but there are no implementations. Did you forget to include a starter?");}if (factories.size() > 1) {// there should only ever be one DiscoveryClient, but there might be more than// one factorylog.warn("More than one implementation " + "of @" + getSimpleName()+ " (now relying on @Conditionals to pick one): " + factories);}return factories.toArray(new String[factories.size()]);}

随后在spring.factories中找到了加载的配置类

org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker=\
org.springframework.cloud.netflix.hystrix.HystrixCircuitBreakerConfiguration

配置类中配置了一个切面HystrixCommandAspect，Hystrix实现的主要功能都在这个切面中进行了执行

    public Object methodsAnnotatedWithHystrixCommand(final ProceedingJoinPoint joinPoint) throws Throwable {Method method = getMethodFromTarget(joinPoint);Validate.notNull(method, "failed to get method from joinPoint: %s", joinPoint);if (method.isAnnotationPresent(HystrixCommand.class) && method.isAnnotationPresent(HystrixCollapser.class)) {throw new IllegalStateException("method cannot be annotated with HystrixCommand and HystrixCollapser " +"annotations at the same time");}MetaHolderFactory metaHolderFactory = META_HOLDER_FACTORY_MAP.get(HystrixPointcutType.of(method));MetaHolder metaHolder = metaHolderFactory.create(joinPoint);HystrixInvokable invokable = HystrixCommandFactory.getInstance().create(metaHolder);ExecutionType executionType = metaHolder.isCollapserAnnotationPresent() ?metaHolder.getCollapserExecutionType() : metaHolder.getExecutionType();Object result;try {if (!metaHolder.isObservable()) {result = CommandExecutor.execute(invokable, executionType, metaHolder);} else {result = executeObservable(invokable, executionType, metaHolder);}} catch (HystrixBadRequestException e) {throw e.getCause();} catch (HystrixRuntimeException e) {throw hystrixRuntimeExceptionToThrowable(metaHolder, e);}return result;}

使用同步调用会走executeObservable最终进入HystrixCommand进入最终的处理逻辑

    public R execute() {try {return queue().get();} catch (Exception e) {throw Exceptions.sneakyThrow(decomposeException(e));}}

进入执行队列并异步获取最后执行 final Futuredelegate = toObservable().toBlocking().toFuture();具体Hystrix中的熔断降级操作即在toObservable()完成

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