docs: show example of tracing over http->grpc boundary

[tmc]

We should show how to propagate an incoming traced http request over the grpc boundary.

Further, perhaps this just be supported out of the box.

[maxkondr]

Is here any news? Any examples,docs will be appreciated

[uschen]

I believe the stackdriver trace works with grpc-gateway.

[maxkondr]

@uschen If I understood correctly, stackdriver works in google cloud and AWS only. I want to use tracing in own solution.

[tmc]

@maxkondr you can use stackdriver trace if your workloads aren't in google's cloud.

[smthpickboy]

Any examples or docs for supporting opentracing? Thanks!

[theRealWardo]

similar to how I solved #7 - I ended up wrapping the mux and writing a little bit of code to propagate the tracing context correctly. here's how I did it:

import (
   ...
   "github.com/opentracing/opentracing-go"
   "github.com/opentracing/opentracing-go/ext"
)

var grpcGatewayTag = opentracing.Tag{Key: string(ext.Component), Value: "grpc-gateway"}

func tracingWrapper(h http.Handler) http.Handler {
  return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    parentSpanContext, err := opentracing.GlobalTracer().Extract(
      opentracing.HTTPHeaders,
      opentracing.HTTPHeadersCarrier(r.Header))
    if err == nil || err == opentracing.ErrSpanContextNotFound {
      serverSpan := opentracing.GlobalTracer().StartSpan(
        "ServeHTTP",
        // this is magical, it attaches the new span to the parent parentSpanContext, and creates an unparented one if empty.
        ext.RPCServerOption(parentSpanContext),
        grpcGatewayTag,
      )
      r = r.WithContext(opentracing.ContextWithSpan(r.Context(), serverSpan))
      defer serverSpan.Finish()
    }
    h.ServeHTTP(w, r)
  })
}

// Then just wrap your mux...
if err := http.ListenAndServe(":8080", tracingWrapper(mux)); err != nil {
  log.Fatalf("failed to start gateway server on 8080: %v", err)
}

[maxkondr]

there is a ready for use solution from github.com/opentracing-contrib/go-stdlib/nethttp lib:

import "github.com/opentracing-contrib/go-stdlib/nethttp"

...
return http.ListenAndServe(fmt.Sprintf(":%d", myPort),
		nethttp.Middleware(
			opentracing.GlobalTracer(),
			mux,
			nethttp.MWComponentName(os.Getenv("MY_POD_NAME")),
		),
	)

[ZachEddy]

Not sure if this is the right place to ask questions, but I didn't know where else to post.

Does the gRPC Gateway client need to be initiated with a tracing interceptor? I struggled to get @theRealWardo's example to work until I added a client-side interceptor. If so, I think it would be helpful to bring this up in the documentation (happy to open a PR for this).

There's some relevant information here, but I wanted to double check.

[johanbrandhorst]

Hi @ZachEddy, we'd happily welcome any documentation improvements you could contribute. I haven't got any experience with this myself so your knowledge would be very good to capture.