Fixing force tracing with Jaeger

CHANGELOG.md

@@ -40,6 +40,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 - [#4779](https://github.com/thanos-io/thanos/pull/4779) Examples: Fix the interactive test for MacOS users.
 - [#4792](https://github.com/thanos-io/thanos/pull/4792) Store: Fix data race in BucketedBytes pool.
 - [#4769](https://github.com/thanos-io/thanos/pull/4769) Query-frontend+api: add "X-Request-ID" field and other fields to start call log.
+- [#4918](https://github.com/thanos-io/thanos/pull/4918) Tracing: Fixing force tracing with Jaeger.
 
 ### Changed
 

pkg/tracing/http.go

@@ -8,6 +8,7 @@ import (
 	"net"
 	"net/http"
 	"strconv"
+	"strings"
 
 	"github.com/go-kit/log"
 	"github.com/go-kit/log/level"
@@ -35,7 +36,7 @@ func HTTPMiddleware(tracer opentracing.Tracer, name string, logger log.Logger, n
 		ext.HTTPUrl.Set(span, r.URL.String())
 
 		// If client specified ForceTracingBaggageKey header, ensure span includes it to force tracing.
-		span.SetBaggageItem(ForceTracingBaggageKey, r.Header.Get(ForceTracingBaggageKey))
+		span.SetBaggageItem(strings.ToLower(ForceTracingBaggageKey), r.Header.Get(ForceTracingBaggageKey))
 
 		if t, ok := tracer.(Tracer); ok {
 			if traceID, ok := t.GetTraceIDFromSpanContext(span.Context()); ok {

pkg/tracing/jaeger/jaeger.go

@@ -7,6 +7,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"strings"
 
 	"github.com/thanos-io/thanos/pkg/tracing"
 
@@ -52,7 +53,7 @@ func NewTracer(ctx context.Context, logger log.Logger, metrics *prometheus.Regis
 	}
 
 	cfg.Headers = &jaeger.HeadersConfig{
-		JaegerDebugHeader: tracing.ForceTracingBaggageKey,
+		JaegerDebugHeader: strings.ToLower(tracing.ForceTracingBaggageKey),
 	}
 	cfg.Headers.ApplyDefaults()
 	jaegerTracer, closer, err = cfg.NewTracer(