Hystrix使用分析

ゞ浴缸里的玫瑰 2023-01-23 09:50 48阅读 0赞

## 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

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 ![file][]

### 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 ![file][file 1]

### 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

@Override
        public 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 duplicates
            List<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 factory
                log.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 Future delegate = toObservable().toBlocking().toFuture();具体Hystrix中的熔断降级操作即在toObservable()完成

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![file][file 2]

[file]: /images/20221004/c5e20348316b42ae866dbe8e2191e6a5.png
[file 1]: /images/20221004/6d8f4ddfef8e418a893f2bd34a21de02.png
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[file 2]: /images/20221004/b2f8140d77a041d39ece5ff6ae601d9a.png