深入Spring Boot:快速集成Dubbo + Hystrix

原文出处:hengyunabc

背景

Dubbo是Alibaba开源的、目前国内最流行的 java RPC 框架。而 Hystrix 旨在通过控制那些访问远程系统、服务和第三方库的节点,从而对延迟和故障提供更强大的容错能力。它具备拥有回退机制和断路器功能的线程和信号隔离,请求缓存和请求打包,以及监控和配置等功能。
本文将介绍在 Spring Boot 中 结合 Dubbo和Hystrix。

  • https://github.com/Netflix/Hystrix
  • https://github.com/apache/incubator-dubbo

为了简化开发,可以在这里直接生成 Spring Boot + dubbo 的工程:http://start.dubbo.io/

配置spring-cloud-starter-netflix-hystrix
Spring Boot 官方提供了对 hystrix 的集成,可以直接在 pom.xml 里加入依赖:

<dependency>
	<groupId>org.springframework.cloud</groupId>
	<artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
	<version>1.4.4.RELEASE</version>
</dependency>

然后在 Spring Boot 启动类上增加 @EnableHystrix 来启用 hystrix starter:

@SpringBootApplication
@EnableHystrix
public class SimpleApplication {

配置Provider端
在Dubbo的Provider上增加 @HystrixCommand 配置,这样子调用就会经过Hystrix代理。

@Service(version = "1.0.0")
public class HelloServiceImpl implements HelloService {
    @HystrixCommand(commandProperties = {
                    @HystrixProperty(name = "circuitBreaker.requestVolumeThreshold", value = "10"),
                    @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "2000") })
    @Override
    public String sayHello(String name) {
        // System.out.println("async provider received: " + name);
        // return "annotation: hello, " + name;
        throw new RuntimeException("Exception to show hystrix enabled.");
    }
}

配置Consumer端
对于Consumer端,则可以增加一层method调用,并在method上配置 @HystrixCommand 。当调用出错时,会走到 fallbackMethod = "reliable" 的调用里。

@Reference(version = "1.0.0")
    private HelloService demoService;

    @HystrixCommand(fallbackMethod = "reliable")
    public String doSayHello(String name) {
        return demoService.sayHello(name);
    }
    public String reliable(String name) {
        return "hystrix fallback value";
    }

通过上面的配置,很简单地就完成了Spring Boot里Dubbo + Hystrix的集成。

传统 Springannotation应用的配置

传统 Springannotation应用的配置其实也很简单,和Spring Boot应用不同的是:

  • 显式配置Spring AOP支持:@EnableAspectJAutoProxy
  • 显式通过 @Configuration 配置 HystrixCommandAspect Bean。
@Configuration
    @EnableDubbo(scanBasePackages = "com.alibaba.dubbo.samples.annotation.action")
    @PropertySource("classpath:/spring/dubbo-consumer.properties")
    @ComponentScan(value = {"com.alibaba.dubbo.samples.annotation.action"})
    @EnableAspectJAutoProxy
    static public class ConsumerConfiguration {

        @Bean
        public HystrixCommandAspect hystrixCommandAspect() {
            return new HystrixCommandAspect();
        }
    }

Hystrix集成Spring AOP原理
在上面的例子里可以看到,Hystrix对Spring的集成是通过Spring AOP来实现的。下面简单分析下实现。

@Aspect
public class HystrixCommandAspect {
    @Pointcut("@annotation(com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand)")
    public void hystrixCommandAnnotationPointcut() {
    }
    @Pointcut("@annotation(com.netflix.hystrix.contrib.javanica.annotation.HystrixCollapser)")
    public void hystrixCollapserAnnotationPointcut() {
    }

    @Around("hystrixCommandAnnotationPointcut() || hystrixCollapserAnnotationPointcut()")
    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() != null ? e.getCause() : e;
        } catch (HystrixRuntimeException e) {
            throw hystrixRuntimeExceptionToThrowable(metaHolder, e);
        }
        return result;
    }
  • HystrixCommandAspect 里定义了两个注解的AspectJ Pointcut:@HystrixCommand, @HystrixCollapser。所有带这两个注解的spring bean都会经过AOP处理

  • @Around AOP 处理函数里,可以看到Hystrix会创建出HystrixInvokable,再通过CommandExecutor来执行。

spring-cloud-starter-netflix-hystrix 的代码分析

@EnableHystrix 引入了 @EnableCircuitBreaker@EnableCircuitBreaker 引入了EnableCircuitBreakerImportSelector @EnableCircuitBreaker

public @interface EnableHystrix {
}
@Import(EnableCircuitBreakerImportSelector.class)
public @interface EnableCircuitBreaker {
}
  • EnableCircuitBreakerImportSelector继承了SpringFactoryImportSelector<EnableCircuitBreaker>,使spring加载 META-INF/spring.factories 里的 EnableCircuitBreaker声明的配置在META-INF/spring.factories里可以找到下面的配置,也就是引入了HystrixCircuitBreakerConfiguration。 org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker=
    org.springframework.cloud.netflix.hystrix.HystrixCircuitBreakerConfiguration

  • 在HystrixCircuitBreakerConfiguration里可以发现创建了HystrixCommandAspect @Configuration
    public class HystrixCircuitBreakerConfiguration {

    @Bean
    public HystrixCommandAspect hystrixCommandAspect() {
    return new HystrixCommandAspect();
    }

可见 spring-cloud-starter-netflix-hystrix 实际上也是创建了 HystrixCommandAspect 来集成Hystrix。

另外 spring-cloud-starter-netflix-hystrix 里还有metrics, health, dashboard等集成。
总结

  • 对于dubbo provider的@Service是一个spring bean,直接在上面配置@HystrixCommand即可
  • 对于dubbo consumer的@Reference,可以通过加一层简单的spring method包装,配置@HystrixCommand 即可
  • Hystrix本身提供HystrixCommandAspect来集成Spring AOP,配置了@HystrixCommand@HystrixCollapser 的 Spring method 都会被Hystrix处理

相关链接

  • https://github.com/Netflix/Hystrix
  • https://github.com/apache/incubator-dubbo
  • http://start.dubbo.io/
  • https://cloud.spring.io/spring-cloud-netflix/single/spring-cloud-netflix.html#_circuit_breaker_hystrix_clients