Expose TraceID and SpanID from SpanContext

[gianarb]

Hello folks! Thanks for all the work you did.

Use Case

I would like to expose the trace_id out from a Span mainly over HTTP header, and I would also like to attach it to the logs that my application generates.

Mainly for support purpose. A developer or a system integrator will be able to communicate the trace_id back to the support team, and it will easy for them to understand what is going on.

Problem

I looked around, and it seems like this information is not accessible from the SpanContext but I had a quick chat with @yurishkuro in the mailing list, and it looks like the specification now covers this use case:

https://github.com/opentracing/specification/blob/master/rfc/trace_identifiers.md#specification-changes

Proposal

I opened this issue to figure out together how we should update the SpanContext interface to cover this use case.

// SpanContext represents Span state that must propagate to descendant Spans and across process
// boundaries (e.g., a <trace_id, span_id, sampled> tuple).
type SpanContext interface {
	// ForeachBaggageItem grants access to all baggage items stored in the
	// SpanContext.
	// The handler function will be called for each baggage key/value pair.
	// The ordering of items is not guaranteed.
	//
	// The bool return value indicates if the handler wants to continue iterating
	// through the rest of the baggage items; for example if the handler is trying to
	// find some baggage item by pattern matching the name, it can return false
	// as soon as the item is found to stop further iterations.
	ForeachBaggageItem(handler func(k, v string) bool)

        SpanID() string
        TraceID() string
}

We can probably add two simple method SpanID() and TraceID() to the SpanContext.

[jcchavezs]

The usual way is that you tag your trace with requestID rather than exposing the traceID because standard does not define it and you might not control de format.

Den tor. 7. jun. 2018, 18:51 skrev Gianluca Arbezzano < [email protected]>:

Hello folks! Thanks for all the work you did. Use Case

I would like to expose the trace_id out from a Span mainly over HTTP header and I would also like to attach it to the logs that my application generates.

Mainly for support purpose. A developer or a system integrator will be able to communicate the trace_id back to the support team and it will easy for them to understand what is going on. Problem

I looked around and it looks like this information are not easy to fetch from a SpanContext but I had quick chat with @yurishkuro https://github.com/yurishkuro in the mailing list and it looks like the specification now covers this use case:

https://github.com/opentracing/specification/blob/master/rfc/trace_identifiers.md Proposal

I opened this issue to figure out together how we should update the SpanContext interface to cover this use case.

// SpanContext represents Span state that must propagate to descendant Spans and across process// boundaries (e.g., a <trace_id, span_id, sampled> tuple).type SpanContext interface { // ForeachBaggageItem grants access to all baggage items stored in the // SpanContext. // The handler function will be called for each baggage key/value pair. // The ordering of items is not guaranteed. // // The bool return value indicates if the handler wants to continue iterating // through the rest of the baggage items; for example if the handler is trying to // find some baggage item by pattern matching the name, it can return false // as soon as the item is found to stop further iterations. ForeachBaggageItem(handler func(k, v string) bool)

    SpanID() string
    TraceID() string

}

We can probably add two simple method SpanID() and TraceID() to the SpanContext.

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[gianarb]

That's a good idea @jcchavezs thanks for sharing your experience. I am gonna do that. But we probably still need to implement the updated spec I think.

Btw storing another tag that behaves like the trace_id is gonna double the size of the index, so at the moment I don't care about the format over to efficiency in the storage. (this obviously depends on storage and tracer but opentracing is ahead of them).

[rafaeljesus]

Some api gateways like traefik for ex opted for using opentracing/jaeger rather than X-Request-Id when proxying request downstream. In my case I want to retrieve the trace ID in the header response making pretty easy to search in Jaeger UI. Here is the work around I came up with:

func NewTracerRequest(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		var span opentracing.Span
		// Attempt to join a trace by getting trace context from the headers.
		carrier := opentracing.HTTPHeadersCarrier(r.Header)
		wireContext, err := opentracing.GlobalTracer().Extract(opentracing.HTTPHeaders, carrier)
		if err != nil {
			span = opentracing.StartSpan(r.URL.Path)
		} else {
			span = opentracing.StartSpan(r.URL.Path, opentracing.ChildOf(wireContext))
		}
		defer span.Finish()

                // code omitted

                span.SetTag("request.id", r.Header.Get("X-Request-Id"))

                // it adds the trace ID to the http headers                
		if err := span.Tracer().Inject(span.Context(), opentracing.HTTPHeaders, carrier); err != nil {
			ext.Error.Set(span, true)
		} else {
			r = r.WithContext(opentracing.ContextWithSpan(r.Context(), span))
		}

		traceID := r.Header.Get("Uber-Trace-Id")
		if traceID != "" {
			traceID = strings.Split(traceID, ":")[0]
			w.Header().Set("X-Trace-Id", traceID)
                         // adds traceID to a context and get from it latter
			r = r.WithContext(tracer.WithContextValue(r.Context(), traceID))
		}

		next.ServeHTTP(w, r)
	})
}

With this approach, being able to join the trace or not the caller will always have the traceID in the response Header

[rafaeljesus]

You can also use @opentracing/basictracer-go

		if sc, ok := span.Context().(basictracer.SpanContext); ok {
			 sc.TraceID
		}

Update: https://godoc.org/github.com/opentracing/basictracer-go#SpanContext

[gianarb]

Probably I am lost, I am just trying to upgrade the opentracing-go lib to catch up with the specification. In this way, I am good without adding any library.

[rafaeljesus]

sounds reasonable, I am neither adding any other lib just to grab the traceID, I wasn't aware of the spec docs you've shared, sound good tho

[yurishkuro]

The main concern is that extending the SpanContext interface in this way is a breaking change that requires a major rev of OpenTracing API. We could implement the identifiers via a separate interface to which the span context could be cast dynamically.

[rafaeljesus]

This is also possible if one is using jaeger and for me works pretty well

		if sc, ok := span.Context().(jaeger.SpanContext); ok {
			sc.TraceID()
		}

[gianarb]

I understand your concern but doing that we are kind of allowing to have 2 version of the ScanContext probably but it is not what the spec says.

But I don't know how you manage this thing. I thought for a second that opentracing-go should be the representation of the spec. But I also understand your concern @yurishkuro .

[yyt030]

@gianarb @yurishkuro So now, I also have the require to print TraceID and SpanID into log files, but not any method or property to do it.

[tedsuo]

If TraceId and SpanID are already in use by jaeger, but with different return types, then we have to pick a different name for the equivalent methods we add to SpanContext. Since this is a cross-language decision, we should continue the debate in the specification repo (and on gitter): https://github.com/opentracing/specification/issues/123

[jcchavezs]

IMHO I don't think we should give counter intuitive names because of a vendor. From OT side we are not introducing a breaking change and in Jaeger side they can use a tag in glide.yml to specify the version.