重庆建站公司费用,设计网页的步骤是什么,国内网页设计优秀案例,把wordpress动静分离背景介绍 目前对于一些非核心操作#xff0c;如增减库存后保存操作日志发送异步消息时#xff08;具体业务流程#xff09;#xff0c;一旦出现MQ服务异常时#xff0c;会导致接口响应超时#xff0c;因此可以考虑对非核心操作引入服务降级、服务隔离。 Hystrix说明
官方…背景介绍 目前对于一些非核心操作如增减库存后保存操作日志发送异步消息时具体业务流程一旦出现MQ服务异常时会导致接口响应超时因此可以考虑对非核心操作引入服务降级、服务隔离。 Hystrix说明
官方文档 Hystrix是Netflix开源的一个容灾框架解决当外部依赖故障时拖垮业务系统、甚至引起雪崩的问题。 为什么需要Hystrix?
在大中型分布式系统中通常系统很多依赖(HTTP,hession,Netty,Dubbo等)在高并发访问下,这些依赖的稳定性与否对系统的影响非常大,但是依赖有很多不可控问题如网络连接缓慢资源繁忙暂时不可用服务脱机等。*当依赖阻塞时,大多数服务器的线程池就出现阻塞(BLOCK),影响整个线上服务的稳定性在复杂的分布式架构的应用程序有很多的依赖都会不可避免地在某些时候失败。高并发的依赖失败时如果没有隔离措施当前应用服务就有被拖垮的风险。
例如:一个依赖30个SOA服务的系统,每个服务99.9999.990.3换算成时间大约每月有2个小时服务不稳定.随着服务依赖数量的变多服务不稳定的概率会成指数性提高.解决问题方案对依赖做隔离。
复制代码Hystrix设计理念 想要知道如何使用必须先明白其核心设计理念Hystrix基于命令模式通过UML图先直观的认识一下这一设计模式。 可见Command是在 Receiver和 Invoker之间添加的中间层 Command实现了对Receiver的封装。API既可以是Invoker又可以是reciever通过继承Hystrix核心类HystrixCommand来封装这些API例如远程接口调用数据库查询之类可能会产生延时的操作。*就可以为API提供弹性保护了。
Hystrix如何解决依赖隔离
Hystrix使用命令模式HystrixCommand(Command)包装依赖调用逻辑每个命令在单独线程中/信号授权下执行。可配置依赖调用超时时间超时时间一般设为比99.5%平均时间略高即可。当调用超时时直接返回或执行fallback逻辑。为每个依赖提供一个小的线程池或信号如果线程池已满调用将被立即拒绝默认不采用排队加速失败判定时间。依赖调用结果分成功失败抛出异常超时线程拒绝短路。 请求失败(异常拒绝超时短路)时执行fallback(降级)逻辑。提供熔断器组件可以自动运行或手动调用停止当前依赖一段时间(10秒)熔断器默认错误率阈值为50%超过将自动运行。提供近实时依赖的统计和监控
Hystrix流程结构解析
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流程说明:
每次调用构建HystrixCommand或者HystrixObservableCommand对象把依赖调用封装在run()方法中.结果是否有缓存如果没有执行execute()/queue做sync或async调用对应真正的run()/construct()判断熔断器(circuit-breaker)是否打开如果打开跳到步骤8进行降级策略如果关闭进入步骤.判断线程池/队列/信号量是否跑满如果跑满进入降级步骤8否则继续后续步骤.使用HystrixObservableCommand.construct()还是HystrixCommand.run()运行依赖逻辑依赖逻辑调用超时进入步骤8判断逻辑是否调用成功
6a 返回成功调用结果6b 调用出错进入步骤8.
计算熔断器状态,所有的运行状态(成功, 失败, 拒绝,超时)上报给熔断器用于统计从而判断熔断器状态.getFallback()降级逻辑. a. 没有实现getFallback的Command将直接抛出异常 b. fallback降级逻辑调用成功直接返回 c. 降级逻辑调用失败抛出异常返回执行成功结果
以下四种情况将触发getFallback调用
run()方法抛出非HystrixBadRequestException异常。run()方法调用超时熔断器开启短路调用线程池/队列/信号量是否跑满
熔断器:Circuit Breaker 每个熔断器默认维护10个bucket每秒一个bucket每个bucket记录成功失败,超时,拒绝的状态默认错误超过50%且10秒内超过20个请求进行中断短路。 Hystrix隔离分析 Hystrix隔离方式采用线程/信号的方式,通过隔离限制依赖的并发量和阻塞扩散. 线程隔离
执行依赖代码的线程与请求线程(如:jetty线程)分离请求线程可以自由控制离开的时间(异步过程)。通过线程池大小可以控制并发量当线程池饱和时可以提前拒绝服务,防止依赖问题扩散。*线上建议线程池不要设置过大否则大量堵塞线程有可能会拖慢服务器。
实际案例 Netflix公司内部认为线程隔离开销足够小不会造成重大的成本或性能的影响。Netflix 内部API 每天100亿的HystrixCommand依赖请求使用线程隔每个应用大约40多个线程池每个线程池大约5-20个线程。 信号隔离 信号隔离也可以用于限制并发访问防止阻塞扩散, 与线程隔离最大不同在于执行依赖代码的线程依然是请求线程该线程需要通过信号申请,如果客户端是可信的且可以快速返回可以使用信号隔离替换线程隔离,降低开销。 信号量的大小可以动态调整, 线程池大小不可以。 线程隔离与信号隔离区别如下图: fallback故障切换降级机制
有兴趣的小伙伴可以看看官方参考文档
源码分析 hystrix-core-1.5.12-sources.jar!/com/netflix/hystrix/AbstractCommand.java executeCommandAndObserve
private Observable executeCommandAndObserve(final AbstractCommand _cmd) {final Func1 handleFallback new Func1() {public Observable call(Throwable t) {circuitBreaker.markNonSuccess();Exception e getExceptionFromThrowable(t);executionResult executionResult.setExecutionException(e);if (e instanceof RejectedExecutionException) {return handleThreadPoolRejectionViaFallback(e);} else if (t instanceof HystrixTimeoutException) {return handleTimeoutViaFallback();} else if (t instanceof HystrixBadRequestException) {return handleBadRequestByEmittingError(e);} else {if (e instanceof HystrixBadRequestException) {eventNotifier.markEvent(HystrixEventType.BAD_REQUEST, commandKey);return Observable.error(e);}return handleFailureViaFallback(e);}}};Observable execution;if (properties.executionTimeoutEnabled().get()) {execution executeCommandWithSpecifiedIsolation(_cmd).lift(new HystrixObservableTimeoutOperator(_cmd));} else {execution executeCommandWithSpecifiedIsolation(_cmd);}return execution.doOnNext(markEmits).doOnCompleted(markOnCompleted).onErrorResumeNext(handleFallback).doOnEach(setRequestContext);}
复制代码使用Observable的onErrorResumeNext里头调用了handleFallbackhandleFallback中区分不同的异常来调用不同的fallback。
RejectedExecutionException调用handleThreadPoolRejectionViaFallbackHystrixTimeoutException调用handleTimeoutViaFallback*非HystrixBadRequestException的调用handleFailureViaFallback
applyHystrixSemantics private Observable applyHystrixSemantics(final AbstractCommand _cmd) {executionHook.onStart(_cmd);if (circuitBreaker.attemptExecution()) {final TryableSemaphore executionSemaphore getExecutionSemaphore();final AtomicBoolean semaphoreHasBeenReleased new AtomicBoolean(false);final Action0 singleSemaphoreRelease new Action0() {public void call() {if (semaphoreHasBeenReleased.compareAndSet(false, true)) {executionSemaphore.release();}}};final Action1 markExceptionThrown new Action1() {public void call(Throwable t) {eventNotifier.markEvent(HystrixEventType.EXCEPTION_THROWN, commandKey);}};if (executionSemaphore.tryAcquire()) {try {executionResult executionResult.setInvocationStartTime(System.currentTimeMillis());return executeCommandAndObserve(_cmd).doOnError(markExceptionThrown).doOnTerminate(singleSemaphoreRelease).doOnUnsubscribe(singleSemaphoreRelease);} catch (RuntimeException e) {return Observable.error(e);}} else {return handleSemaphoreRejectionViaFallback();}} else {return handleShortCircuitViaFallback();}}
复制代码applyHystrixSemantics方法针对executionSemaphore.tryAcquire()没通过的调用handleSemaphoreRejectionViaFallbackapplyHystrixSemantics方法针对circuitBreaker.attemptExecution()没通过的调用handleShortCircuitViaFallback()
ViaFallback方法 private Observable handleSemaphoreRejectionViaFallback() {Exception semaphoreRejectionException new RuntimeException(could not acquire a semaphore for execution);executionResult executionResult.setExecutionException(semaphoreRejectionException);eventNotifier.markEvent(HystrixEventType.SEMAPHORE_REJECTED, commandKey);logger.debug(HystrixCommand Execution Rejection by Semaphore.);return getFallbackOrThrowException(this, HystrixEventType.SEMAPHORE_REJECTED, FailureType.REJECTED_SEMAPHORE_EXECUTION,could not acquire a semaphore for execution, semaphoreRejectionException);}private Observable handleShortCircuitViaFallback() {eventNotifier.markEvent(HystrixEventType.SHORT_CIRCUITED, commandKey);Exception shortCircuitException new RuntimeException(Hystrix circuit short-circuited and is OPEN);executionResult executionResult.setExecutionException(shortCircuitException);try {return getFallbackOrThrowException(this, HystrixEventType.SHORT_CIRCUITED, FailureType.SHORTCIRCUIT,short-circuited, shortCircuitException);} catch (Exception e) {return Observable.error(e);}}private Observable handleThreadPoolRejectionViaFallback(Exception underlying) {eventNotifier.markEvent(HystrixEventType.THREAD_POOL_REJECTED, commandKey);threadPool.markThreadRejection();return getFallbackOrThrowException(this, HystrixEventType.THREAD_POOL_REJECTED, FailureType.REJECTED_THREAD_EXECUTION, could not be queued for execution, underlying);}private Observable handleTimeoutViaFallback() {return getFallbackOrThrowException(this, HystrixEventType.TIMEOUT, FailureType.TIMEOUT, timed-out, new TimeoutException());}private Observable handleFailureViaFallback(Exception underlying) {logger.debug(Error executing HystrixCommand.run(). Proceeding to fallback logic ..., underlying);eventNotifier.markEvent(HystrixEventType.FAILURE, commandKey);executionResult executionResult.setException(underlying);return getFallbackOrThrowException(this, HystrixEventType.FAILURE, FailureType.COMMAND_EXCEPTION, failed, underlying);}
复制代码handleSemaphoreRejectionViaFallback、handleShortCircuitViaFallback、handleThreadPoolRejectionViaFallback、handleTimeoutViaFallback、handleFailureViaFallback这几个方法调用了getFallbackOrThrowException其eventType分别是SEMAPHORE_REJECTED、SHORT_CIRCUITED、THREAD_POOL_REJECTED、TIMEOUT、FAILUREAbstractCommand.getFallbackOrThrowException hystrix-core-1.5.12-sources.jar!/com/netflix/hystrix/AbstractCommand.java private Observable getFallbackOrThrowException(final AbstractCommand _cmd, final HystrixEventType eventType, final FailureType failureType, final String message, final Exception originalException) {final HystrixRequestContext requestContext HystrixRequestContext.getContextForCurrentThread();long latency System.currentTimeMillis() - executionResult.getStartTimestamp();executionResult executionResult.addEvent((int) latency, eventType);if (isUnrecoverable(originalException)) {logger.error(Unrecoverable Error for HystrixCommand so will throw HystrixRuntimeException and not apply fallback. , originalException);Exception e wrapWithOnErrorHook(failureType, originalException);return Observable.error(new HystrixRuntimeException(failureType, this.getClass(), getLogMessagePrefix() message and encountered unrecoverable error., e, null));} else {if (isRecoverableError(originalException)) {logger.warn(Recovered from java.lang.Error by serving Hystrix fallback, originalException);}if (properties.fallbackEnabled().get()) {final Action1super R setRequestContext new Action1super R() {public void call(Notificationsuper R rNotification) {setRequestContextIfNeeded(requestContext);}};final Action1 markFallbackEmit new Action1() {public void call(R r) {if (shouldOutputOnNextEvents()) {executionResult executionResult.addEvent(HystrixEventType.FALLBACK_EMIT);eventNotifier.markEvent(HystrixEventType.FALLBACK_EMIT, commandKey);}}};final Action0 markFallbackCompleted new Action0() {public void call() {long latency System.currentTimeMillis() - executionResult.getStartTimestamp();eventNotifier.markEvent(HystrixEventType.FALLBACK_SUCCESS, commandKey);executionResult executionResult.addEvent((int) latency,HystrixEventType.FALLBACK_SUCCESS);}};final Func1 handleFallbackError new Func1() {public Observable call(Throwable t) {Exception e wrapWithOnErrorHook(failureType, originalException);Exception fe getExceptionFromThrowable(t);long latency System.currentTimeMillis() - executionResult.getStartTimestamp();Exception toEmit;if (fe instanceof UnsupportedOperationException) {logger.debug(No fallback for HystrixCommand. , fe);eventNotifier.markEvent(HystrixEventType.FALLBACK_MISSING, commandKey);executionResult executionResult.addEvent((int) latency, HystrixEventType.FALLBACK_MISSING);toEmit new HystrixRuntimeException(failureType, _cmd.getClass(), getLogMessagePrefix() message and no fallback available., e, fe);} else {logger.debug(HystrixCommand execution failureType.name() and fallback failed., fe);eventNotifier.markEvent(HystrixEventType.FALLBACK_FAILURE, commandKey);executionResult executionResult.addEvent((int) latency, HystrixEventType.FALLBACK_FAILURE);toEmit new HystrixRuntimeException(failureType, _cmd.getClass(), getLogMessagePrefix() message and fallback failed., e, fe);}if (shouldNotBeWrapped(originalException)) {return Observable.error(e);}return Observable.error(toEmit);}};final TryableSemaphore fallbackSemaphore getFallbackSemaphore();final AtomicBoolean semaphoreHasBeenReleased new AtomicBoolean(false);final Action0 singleSemaphoreRelease new Action0() {public void call() {if (semaphoreHasBeenReleased.compareAndSet(false, true)) {fallbackSemaphore.release();}}};Observable fallbackExecutionChain;if (fallbackSemaphore.tryAcquire()) {try {if (isFallbackUserDefined()) {executionHook.onFallbackStart(this);fallbackExecutionChain getFallbackObservable();} else {fallbackExecutionChain getFallbackObservable();}} catch (Throwable ex) {fallbackExecutionChain Observable.error(ex);}return fallbackExecutionChain.doOnEach(setRequestContext).lift(new FallbackHookApplication(_cmd)).lift(new DeprecatedOnFallbackHookApplication(_cmd)).doOnNext(markFallbackEmit).doOnCompleted(markFallbackCompleted).onErrorResumeNext(handleFallbackError).doOnTerminate(singleSemaphoreRelease).doOnUnsubscribe(singleSemaphoreRelease);} else {return handleFallbackRejectionByEmittingError();}} else {return handleFallbackDisabledByEmittingError(originalException, failureType, message);}}}
复制代码fallbackExecutionChain的onErrorResumeNext调用了handleFallbackErrorfallbackExecutionChain的doOnCompleted调用了markFallbackCompletedAbstractCommand.getFallbackSemaphore hystrix-core-1.5.12-sources.jar!/com/netflix/hystrix/AbstractCommand.java protected TryableSemaphore getFallbackSemaphore() {if (fallbackSemaphoreOverride null) {TryableSemaphore _s fallbackSemaphorePerCircuit.get(commandKey.name());if (_s null) {fallbackSemaphorePerCircuit.putIfAbsent(commandKey.name(), new TryableSemaphoreActual(properties.fallbackIsolationSemaphoreMaxConcurrentRequests()));return fallbackSemaphorePerCircuit.get(commandKey.name());} else {return _s;}} else {return fallbackSemaphoreOverride;}}
复制代码针对每个commandKey获取或创建TryableSemaphoreActual fallback源码分析小结
hystrix的fallback主要分为5种类型
SEMAPHORE_REJECTED对应handleSemaphoreRejectionViaFallbackSHORT_CIRCUITED对应handleShortCircuitViaFallbackTHREAD_POOL_REJECTED对应handleThreadPoolRejectionViaFallbackTIMEOUT对应handleTimeoutViaFallbackFAILURE对应handleFailureViaFallback这几个方法最后都调用了getFallbackOrThrowException方法。 分享资源 获取以上资源请访问开源项目 点击跳转
