使用Hystrix实现自动降级与依赖隔离[微服务]

官方文档 [https://github.com/Netflix/Hystrix/wiki]

例如:一个依赖30个SOA服务的系统,每个服务99.99%可用。
99.99%的30次方 ≈ 99.7%
0.3% 意味着一亿次请求 会有 3,000,00次失败
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.

流程说明:
1:每次调用创建一个新的HystrixCommand,把依赖调用封装在run()方法中.
2:执行execute()/queue做同步或异步调用.
3: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.
4: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.
5:调用HystrixCommand的run方法.运行依赖逻辑
5a:依赖逻辑调用超时,进入步骤8.
6: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.
7: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.
8:getFallback()降级逻辑.
  以下四种情况将触发getFallback调用：
 (1):run()方法抛出非HystrixBadRequestException异常。
 (2):run()方法调用超时
 (3):熔断器开启拦截调用
 (4):线程池/队列/信号量是否跑满
8a:没有实现getFallback的Command将直接抛出异常
8b:fallback降级逻辑调用成功直接返回
8c:降级逻辑调用失败抛出异常
9:返回执行成功结果

<hystrix-version>1.4.22</hystrix-version>
  
<dependency>
    <groupId>com.netflix.hystrix</groupId>
    <artifactId>hystrix-core</artifactId>
    <version>${hystrix-version}</version>
</dependency>
<dependency>
    <groupId>com.netflix.hystrix</groupId>
    <artifactId>hystrix-metrics-event-stream</artifactId>
    <version>${hystrix-version}</version>
</dependency>
<dependency>
    <groupId>com.netflix.hystrix</groupId>
    <artifactId>hystrix-javanica</artifactId>
    <version>${hystrix-version}</version>
</dependency>
<dependency>
    <groupId>com.netflix.hystrix</groupId>
    <artifactId>hystrix-servo-metrics-publisher</artifactId>
    <version>${hystrix-version}</version>
</dependency>
<dependency>
    <groupId>com.meituan.service.us</groupId>
    <artifactId>hystrix-collector</artifactId>
    <version>1.0-SNAPSHOT</version>
</dependency>

<aop:aspectj-autoproxy/>
<bean id="hystrixAspect" class="com.netflix.hystrix.contrib.javanica.aop.aspectj.HystrixCommandAspect"></bean>
<context:component-scan base-package="com.***.***"/>
<context:annotation-config/>

import com.meituan.service.us.collector.notifier.CustomEventNotifier;
import com.netflix.hystrix.contrib.servopublisher.HystrixServoMetricsPublisher;
import com.netflix.hystrix.strategy.HystrixPlugins;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.InitializingBean;
 
/**
 * Created by gaoguangchao on 16/7/1.
 */
public class HystrixMetricsInitializingBean {
    private static final Logger LOGGER = LoggerFactory.getLogger(HystrixMetricsInitializingBean.class);
 
    public void init() throws Exception {
        LOGGER.info("HystrixMetrics starting...");
        HystrixPlugins.getInstance().registerEventNotifier(CustomEventNotifier.getInstance());
        HystrixPlugins.getInstance().registerMetricsPublisher(HystrixServoMetricsPublisher.getInstance());
    }
}

<bean id="hystrixMetricsInitializingBean" class="com.***.HystrixMetricsInitializingBean" init-method="init"/>

@HystrixCommand(groupKey = "productStockOpLog", commandKey = "addProductStockOpLog", fallbackMethod = "addProductStockOpLogFallback",
        commandProperties = {
                @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "400"),//指定多久超时，单位毫秒。超时进fallback
                @HystrixProperty(name = "circuitBreaker.requestVolumeThreshold", value = "10"),//判断熔断的最少请求数，默认是10；只有在一个统计窗口内处理的请求数量达到这个阈值，才会进行熔断与否的判断
                @HystrixProperty(name = "circuitBreaker.errorThresholdPercentage", value = "10"),//判断熔断的阈值，默认值50，表示在一个统计窗口内有50%的请求处理失败，会触发熔断
        }
)
public void addProductStockOpLog(Long sku_id, Object old_value, Object new_value) throws Exception {
    if (new_value != null && !new_value.equals(old_value)) {
        doAddOpLog(null, null, sku_id, null, ProductOpType.PRODUCT_STOCK, old_value != null ? String.valueOf(old_value) : null, String.valueOf(new_value), 0, "C端", null);
    }
}
 
public void addProductStockOpLogFallback(Long sku_id, Object old_value, Object new_value) throws Exception {
    LOGGER.warn("发送商品库存变更消息失败,进入Fallback,skuId:{},oldValue:{},newValue:{}", sku_id, old_value, new_value);
}

@HystrixCommand(groupKey="UserGroup", commandKey = "GetUserByIdCommand"，
                commandProperties = {
                    @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "100"),//指定多久超时，单位毫秒。超时进fallback
                    @HystrixProperty(name = "circuitBreaker.requestVolumeThreshold", value = "10"),//判断熔断的最少请求数，默认是10；只有在一个统计窗口内处理的请求数量达到这个阈值，才会进行熔断与否的判断
                    @HystrixProperty(name = "circuitBreaker.errorThresholdPercentage", value = "10"),//判断熔断的阈值，默认值50，表示在一个统计窗口内有50%的请求处理失败，会触发熔断
                },
                threadPoolProperties = {
                        @HystrixProperty(name = "coreSize", value = "30"),
                        @HystrixProperty(name = "maxQueueSize", value = "101"),
                        @HystrixProperty(name = "keepAliveTimeMinutes", value = "2"),
                        @HystrixProperty(name = "queueSizeRejectionThreshold", value = "15"),
                        @HystrixProperty(name = "metrics.rollingStats.numBuckets", value = "12"),
                        @HystrixProperty(name = "metrics.rollingStats.timeInMilliseconds", value = "1440")
        })