Pass trace data via @HystrixCommand about spring-cloud-sleuth HOT 15 CLOSED

See Netflix/Hystrix#92 (comment)

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I've read the issues, and also taken a look at your extension of HistrixCommand. What is the purpouse of this extension?

What should be use on combimatiom with @HistrixCommamd to allow tracing happen? Should a custom concurrent strategy be implememted?

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@morfeo8marc the purpose of the extension is to use is when you construct a HystrixCommand by hand. This issue is to support passing trace data via @HystrixCommand.

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Just ran into this issue. 👍

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When this is implemented, will it handle the case where Hystrix isolation policy is THREAD? I tried using extending TraceCommand instead of annotating with @HystrixCommand and while it does create a span, the trace context is not passed to Hystrix's child thread so the parent/child relationship between spans is lost.

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The workaround of using a custom ConcurrencyStrategy works for this case:

hystrix.plugin.HystrixConcurrencyStrategy.implementation=SpanPreservingConcurrencyStrategy

This would be the implementation:

public class SpanPreservingConcurrencyStrategy extends HystrixConcurrencyStrategy {
    @Override
    public <T> Callable<T> wrapCallable(Callable<T> callable) {
        return new SpanPreservingCallable<T>(callable);
    }

    public static class SpanPreservingCallable<T> implements Callable<T> {
        private Span currentSpan;
        private Callable<T> callable;

        public SpanPreservingCallable(Callable<T> callable) {
            this.callable = callable;
            this.currentSpan = TraceContextHolder.getCurrentSpan();
        }

        @Override
        public T call() throws Exception {
            // set span of the calling thread
            TraceContextHolder.setCurrentSpan(currentSpan);
            try {
                return callable.call();
            } finally {
                // reset span
                TraceContextHolder.setCurrentSpan(null);
            }
        }
    }
}

I've tried to make this more extensible so it could be included in spring-cloud-netflix, but I've encountered several problems as this class is instantiated by Hystrix and not by Spring...

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I agree, one question though: How would this work if the HystrixCommand does a network call? In that case you'd end up with 2 spans which might be overkill?

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Here's a collapsing example, the UI is trained to expand only nodes involving a service is involved in, "lorem" in this case. I clicked on collapse all, and then clicked on "lorem" which expanded paths to it.

Then, I clicked "vitae" which had multiple paths.

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The solution from @swehner seems like a good idea. The only problem I see is when someone already has a custom strategy.

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@spencergibb , @dsyer , @adriancole In this commit I've done an initial approach with a test that I guess proves that it's working - 6ecfbca . WDYT about this?

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Done here - #78

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