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
@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<R> delegate = toObservable().toBlocking().toFuture();具体Hystrix中的熔断降级操作即在toObservable()完成
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