Trace context is not propagating to the http request (using NewRequestWithContext)

[jaisonsteephen]

Hi, I am using otelecho.Middleware to trace my request from service1(in go) to service2(in java)
But trace context is not propagating. Could you please help to to identify the issue. thanks in advance.
Hope we don't need to manually extract and inject spans.

Please see my code below

package main

import (
	"context"
	"log"
	"net/http"
	"fmt"
	"io/ioutil"
	"github.com/labstack/echo/v4"

	"go.opentelemetry.io/contrib/instrumentation/github.com/labstack/echo/otelecho"
	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/propagation"
	sdktrace "go.opentelemetry.io/otel/sdk/trace"
	"go.opentelemetry.io/otel/exporters/jaeger"
)


var HTTPClient = &http.Client{}
var Client = HTTPClient.Do

func main() {
	tp := initTracer()
	defer func() {
		if err := tp.Shutdown(context.Background()); err != nil {
			log.Printf("Error shutting down tracer provider: %v", err)
		}
	}()
	r := echo.New()
	r.Use(otelecho.Middleware("my-go-server"))

	r.GET("/hiGoService", func(c echo.Context) error {
		getJavaService(c.Request().Context())
		return nil
	})
	_ = r.Start(":8080")
}

func initTracer() *sdktrace.TracerProvider {
	exporter, err := jaeger.New(
		jaeger.WithCollectorEndpoint(),
	)
	if err != nil {
		log.Fatal(err)
	}
	tp := sdktrace.NewTracerProvider(
		sdktrace.WithSampler(sdktrace.AlwaysSample()),
		sdktrace.WithBatcher(exporter),
	)
	otel.SetTracerProvider(tp)
	otel.SetTextMapPropagator(propagation.NewCompositeTextMapPropagator(propagation.TraceContext{}, propagation.Baggage{}))
	return tp
}


func getJavaService(ctx context.Context) error {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, "http://localhost:8013/hiJava", nil)
	resp, err := Client(req)
	if err != nil {
		return nil
	} else if resp.StatusCode == 201 || resp.StatusCode == 200 || resp.StatusCode == 204 {
		fmt.Println(resp.StatusCode)
		bodyBytes, _ := ioutil.ReadAll(resp.Body)
		bodyString := string(bodyBytes)
		fmt.Println(bodyString)
	}
	return nil
}

[jaisonsteephen]

I got the answer for my query
Need to use client like below

client := http.Client{Transport: otelhttp.NewTransport(http.DefaultTransport)}
req, _ := http.NewRequestWithContext(ctx, "GET", url, nil)

[ianling]

For any future readers struggling with this, you MUST use http.NewRequestWithContext, attempting to inject the context via req.WithContext or req.Clone does not work, for some reason.

[ianling]

@MrAlias do you happen to have any idea why this is?

client := http.Client{Transport: otelhttp.NewTransport(http.DefaultTransport)}

// this does not work
req, _ := http.NewRequest(...)
req = req.WithContext(ctx)

// neither does this
req, _ := http.NewRequest(...)
req = req.Clone(ctx)

// but this does
req, _ := http.NewRequestWithContext(ctx, ...)

// in any case... finally:
client.Do(req)

[MrAlias]

@ianling can you provide a complete example? I am not aware of any issues propagating span context if using WithContext or Clone. Both have worked for me in the past.

[pellared]

@ianling in your examples you are not using the client that you have created in the first line. The only thing I remember is that otelhttp requires calling resp.Body.Close().