微服务全链路跟踪：jaeger集成hystrix

背景

> 当springcloud服务集成hystrix，并且用了hystrixCommend注解到方法上时，jaeger链路会断掉

方案

在网上搜索到了大量jaeger遇到多线程时的处理方式，都是包装线程池来做到ThreadLocal传递，有很多都用到了阿里开源的transmittable-thread-local。

下面说一下当集成hystrix时，jaeger链路丢失问题，大家都知道hystrix默认是线程池隔离，所以归根结底还是遇到多线程线程变量没有共享的问题，网上也罗列了几种方案：

方案一：变更隔离方式

hystrix.command.default.execution.isolation.strategy: SEMAPHORE

当并发高时这里设置信号量隔离是有风险的，可以根据情况优化断路器配置来降低风险

方案二：自定义隔离策略

隔离策略官方文档有定义：

原先我就定义了一个feign传递request中header信息的策略，在原有的隔离策略下面参考https://github.com/opentracing-contrib/java-concurrent项目的代码：

将原有feign自定义隔离策略做了响应变动，代码如下

/**
 * 自定义Feign的隔离策略:
 *   在转发Feign的请求头的时候, 如果开启了Hystrix,
 *      Hystrix的默认隔离策略是Thread(线程隔离策略), 因此转发拦截器内是无法获取到请求的请求头信息的,
 *      可以修改默认隔离策略为信号量模式：hystrix.command.default.execution.isolation.strategy=SEMAPHORE,
 *      这样的话转发线程和请求线程实际上是一个线程, 这并不是最好的解决方法, 信号量模式也不是官方最为推荐的隔离策略;
 *   另一个解决方法就是自定义Hystrix的隔离策略:
 *      思路是将现有的并发策略作为新并发策略的成员变量,在新并发策略中,
 *      返回现有并发策略的线程池、Queue;将策略加到Spring容器即可;
 */
@Component
@Slf4j
public class FeignHystrixConcurrencyStrategy extends HystrixConcurrencyStrategy {
    private HystrixConcurrencyStrategy delegate;
    @Lazy
    @Autowired
    private Tracer tracer;
    public FeignHystrixConcurrencyStrategy() {
        try {
            this.delegate = HystrixPlugins.getInstance().getConcurrencyStrategy();
            if (this.delegate instanceof FeignHystrixConcurrencyStrategy) {
                // Welcome to singleton hell...
                return;
            }
            HystrixCommandExecutionHook commandExecutionHook =
                    HystrixPlugins.getInstance().getCommandExecutionHook();
            HystrixEventNotifier eventNotifier = HystrixPlugins.getInstance().getEventNotifier();
            HystrixMetricsPublisher metricsPublisher = HystrixPlugins.getInstance().getMetricsPublisher();
            HystrixPropertiesStrategy propertiesStrategy =
                    HystrixPlugins.getInstance().getPropertiesStrategy();
            this.logCurrentStateOfHystrixPlugins(eventNotifier, metricsPublisher, propertiesStrategy);
            HystrixPlugins.reset();
            HystrixPlugins instance = HystrixPlugins.getInstance();
            instance.registerConcurrencyStrategy(this);
            instance.registerCommandExecutionHook(commandExecutionHook);
            instance.registerEventNotifier(eventNotifier);
            instance.registerMetricsPublisher(metricsPublisher);
            instance.registerPropertiesStrategy(propertiesStrategy);
        } catch (Exception e) {
            log.error("Failed to register Sleuth Hystrix Concurrency Strategy", e);
        }
    }
    private void logCurrentStateOfHystrixPlugins(HystrixEventNotifier eventNotifier,
                                                 HystrixMetricsPublisher metricsPublisher,
                                                 HystrixPropertiesStrategy propertiesStrategy) {
        if (log.isDebugEnabled()) {
            log.debug("Current Hystrix plugins configuration is [" + "concurrencyStrategy ["
                    + this.delegate + "]," + "eventNotifier [" + eventNotifier + "]," + "metricPublisher ["
                    + metricsPublisher + "]," + "propertiesStrategy [" + propertiesStrategy + "]," + "]");
            log.debug("Registering Sleuth Hystrix Concurrency Strategy.");
        }
    }
    @Override
    public <t> Callable<t> wrapCallable(Callable<t> callable) {
        RequestAttributes requestAttributes = RequestContextHolder.getRequestAttributes();
        return new WrappedCallable&lt;&gt;(callable, requestAttributes,tracer,tracer.activeSpan());
    }
    @Override
    public ThreadPoolExecutor getThreadPool(HystrixThreadPoolKey threadPoolKey,
                                            HystrixProperty<integer> corePoolSize,
                                            HystrixProperty<integer> maximumPoolSize,
                                            HystrixProperty<integer> keepAliveTime,
                                            TimeUnit unit, BlockingQueue<runnable> workQueue) {
        return this.delegate.getThreadPool(threadPoolKey, corePoolSize, maximumPoolSize, keepAliveTime,
                unit, workQueue);
    }
    @Override
    public ThreadPoolExecutor getThreadPool(HystrixThreadPoolKey threadPoolKey,
                                            HystrixThreadPoolProperties threadPoolProperties) {
        return this.delegate.getThreadPool(threadPoolKey, threadPoolProperties);
    }
    @Override
    public BlockingQueue<runnable> getBlockingQueue(int maxQueueSize) {
        return this.delegate.getBlockingQueue(maxQueueSize);
    }
    @Override
    public <t> HystrixRequestVariable<t> getRequestVariable(HystrixRequestVariableLifecycle<t> rv) {
        return this.delegate.getRequestVariable(rv);
    }
    static class WrappedCallable<t> implements Callable<t> {
        private final Callable<t> target;
        private final RequestAttributes requestAttributes;
        private final Span span;
        private final Tracer tracer;
        public WrappedCallable(Callable<t> target, RequestAttributes requestAttributes,Tracer tracer, Span span) {
            this.target = target;
            this.requestAttributes = requestAttributes;
            this.tracer=tracer;
            this.span=span;
        }
        @Override
        public T call() throws Exception {
            Scope scope = span == null ? null : tracer.scopeManager().activate(span);
            try {
                RequestContextHolder.setRequestAttributes(requestAttributes);
                return target.call();
            } finally {
                RequestContextHolder.resetRequestAttributes();
                if (scope != null) {
                    scope.close();
                }
            }
        }
    }
}

其中改动部分就是在原有的WrappedCallable中增加了span、trace的注入。

至于自定义隔离策略以及Callable是可以支持多个链的，这里不做详细描述，大家有兴趣可以参考，下面的链接：

https://blog.csdn.net/songhaifengshuaige/article/details/80345012

https://www.jianshu.com/p/c60fe209a799

https://www.cnblogs.com/duanxz/p/10949816.html