feat: add explicit tracer header (#117686)

* feat: add explicit tracer header

* update-workspace

* chore: review feedback

* update workspace

pkg/apiserver/endpoints/filters/upstream_trace_link.go

@@ -0,0 +1,28 @@
+package filters
+
+import (
+	"net/http"
+
+	"go.opentelemetry.io/otel/propagation"
+	"go.opentelemetry.io/otel/trace"
+)
+
+// WithExtractUpstreamTraceLink extracts the Grafana-Upstream-Traceparent
+// custom header (injected by the ST proxy) and adds a span link to the
+// current span. This preserves trace relationships across the vanilla K8s
+// API server, which drops incoming W3C trace context.
+func WithExtractUpstreamTraceLink(handler http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		upstreamTP := req.Header.Get("Grafana-Upstream-Traceparent")
+		if upstreamTP != "" {
+			prop := propagation.TraceContext{}
+			carrier := propagation.MapCarrier{"traceparent": upstreamTP}
+			extractedCtx := prop.Extract(req.Context(), carrier)
+			if sc := trace.SpanContextFromContext(extractedCtx); sc.IsValid() && sc.IsRemote() {
+				currentSpan := trace.SpanFromContext(req.Context())
+				currentSpan.AddLink(trace.Link{SpanContext: sc})
+			}
+		}
+		handler.ServeHTTP(w, req)
+	})
+}

pkg/apiserver/endpoints/filters/upstream_trace_link_test.go

@@ -0,0 +1,94 @@
+package filters
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	sdktrace "go.opentelemetry.io/otel/sdk/trace"
+	"go.opentelemetry.io/otel/sdk/trace/tracetest"
+)
+
+func TestWithExtractUpstreamTraceLink(t *testing.T) {
+	tests := []struct {
+		name         string
+		headerValue  string
+		expectLink   bool
+		expectCalled bool
+	}{
+		{
+			name:         "valid upstream traceparent adds span link",
+			headerValue:  "00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01",
+			expectLink:   true,
+			expectCalled: true,
+		},
+		{
+			name:         "missing header is a no-op",
+			headerValue:  "",
+			expectLink:   false,
+			expectCalled: true,
+		},
+		{
+			name:         "invalid traceparent is a no-op",
+			headerValue:  "not-a-valid-traceparent",
+			expectLink:   false,
+			expectCalled: true,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			recorder := tracetest.NewSpanRecorder()
+			tp := sdktrace.NewTracerProvider(sdktrace.WithSpanProcessor(recorder))
+			tracer := tp.Tracer("test")
+
+			called := false
+			inner := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				called = true
+				w.WriteHeader(http.StatusOK)
+			})
+
+			handler := WithExtractUpstreamTraceLink(inner)
+
+			req := httptest.NewRequest(http.MethodGet, "/test", nil)
+			if tc.headerValue != "" {
+				req.Header.Set("Grafana-Upstream-Traceparent", tc.headerValue)
+			}
+
+			// Start a span to simulate WithTracing having already run.
+			ctx, span := tracer.Start(req.Context(), "test-span")
+			req = req.WithContext(ctx)
+
+			rr := httptest.NewRecorder()
+			handler.ServeHTTP(rr, req)
+
+			span.End()
+
+			if called != tc.expectCalled {
+				t.Errorf("expected inner handler called=%v, got %v", tc.expectCalled, called)
+			}
+
+			spans := recorder.Ended()
+			if len(spans) != 1 {
+				t.Fatalf("expected 1 span, got %d", len(spans))
+			}
+
+			links := spans[0].Links()
+			if tc.expectLink {
+				if len(links) != 1 {
+					t.Fatalf("expected 1 span link, got %d", len(links))
+				}
+				if got := links[0].SpanContext.TraceID().String(); got != "4bf92f3577b34da6a3ce929d0e0e4736" {
+					t.Errorf("unexpected link trace ID: %s", got)
+				}
+				if got := links[0].SpanContext.SpanID().String(); got != "00f067aa0ba902b7" {
+					t.Errorf("unexpected link span ID: %s", got)
+				}
+			} else {
+				if len(links) != 0 {
+					t.Errorf("expected no span links, got %d", len(links))
+				}
+			}
+		})
+	}
+}

pkg/apiserver/go.mod

@@ -10,6 +10,7 @@ require (
 	github.com/stretchr/testify v1.11.1
 	go.opentelemetry.io/contrib/propagators/jaeger v1.39.0
 	go.opentelemetry.io/otel v1.40.0
+	go.opentelemetry.io/otel/sdk v1.40.0
 	go.opentelemetry.io/otel/trace v1.40.0
 	k8s.io/apimachinery v0.35.1
 	k8s.io/apiserver v0.35.1
@@ -84,7 +85,6 @@ require (
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.40.0 // indirect
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.40.0 // indirect
 	go.opentelemetry.io/otel/metric v1.40.0 // indirect
-	go.opentelemetry.io/otel/sdk v1.40.0 // indirect
 	go.opentelemetry.io/proto/otlp v1.9.0 // indirect
 	go.uber.org/multierr v1.11.0 // indirect
 	go.uber.org/zap v1.27.1 // indirect