Record trace id and EntryPoint span id into access log

docs/content/observability/access-logs.md

@@ -250,6 +250,8 @@ accessLog:
     | `TLSVersion`            | The TLS version used by the connection (e.g. `1.2`) (if connection is TLS).                                                                                         |
     | `TLSCipher`             | The TLS cipher used by the connection (e.g. `TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA`) (if connection is TLS)                                                           |
     | `TLSClientSubject`      | The string representation of the TLS client certificate's Subject (e.g. `CN=username,O=organization`)                                                               |
+    | `TraceId`               | A consistent identifier for tracking requests across services, including upstream ones managed by Traefik, shown as a 32-hex digit string                           |
+    | `SpanId`                | A unique identifier for Traefik’s root span (EntryPoint) within a request trace, formatted as a 16-hex digit string.                                                |
 
 ## Log Rotation
 

pkg/middlewares/accesslog/logdata.go

@@ -77,6 +77,11 @@ const (
 	TLSCipher = "TLSCipher"
 	// TLSClientSubject is the string representation of the TLS client certificate's Subject.
 	TLSClientSubject = "TLSClientSubject"
+
+	// TraceID is the consistent identifier for tracking requests across services, including upstream ones managed by Traefik, shown as a 32-hex digit string.
+	TraceID = "TraceId"
+	// SpanID is the unique identifier for Traefik’s root span (EntryPoint) within a request trace, formatted as a 16-hex digit string.
+	SpanID = "SpanId"
 )
 
 // These are written out in the default case when no config is provided to specify keys of interest.

pkg/middlewares/observability/entrypoint.go

@@ -11,6 +11,7 @@ import (
 	"github.com/containous/alice"
 	"github.com/traefik/traefik/v3/pkg/metrics"
 	"github.com/traefik/traefik/v3/pkg/middlewares"
+	"github.com/traefik/traefik/v3/pkg/middlewares/accesslog"
 	"github.com/traefik/traefik/v3/pkg/tracing"
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/metric"
@@ -69,6 +70,12 @@ func (e *entryPointTracing) ServeHTTP(rw http.ResponseWriter, req *http.Request)
 
 	e.tracer.CaptureServerRequest(span, req)
 
+	if logData := accesslog.GetLogData(req); logData != nil {
+		spanContext := span.SpanContext()
+		logData.Core[accesslog.TraceID] = spanContext.TraceID().String()
+		logData.Core[accesslog.SpanID] = spanContext.SpanID().String()
+	}
+
 	recorder := newStatusCodeRecorder(rw, http.StatusOK)
 	e.next.ServeHTTP(recorder, req)
 

pkg/middlewares/observability/entrypoint_test.go

@@ -11,6 +11,7 @@ import (
 	"github.com/stretchr/testify/require"
 	ptypes "github.com/traefik/paerser/types"
 	"github.com/traefik/traefik/v3/pkg/metrics"
+	"github.com/traefik/traefik/v3/pkg/middlewares/accesslog"
 	"github.com/traefik/traefik/v3/pkg/tracing"
 	"github.com/traefik/traefik/v3/pkg/types"
 	"go.opentelemetry.io/otel/attribute"
@@ -181,3 +182,27 @@ func TestEntryPointMiddleware_metrics(t *testing.T) {
 		})
 	}
 }
+
+func TestEntryPointMiddleware_tracingInfoIntoLog(t *testing.T) {
+	req := httptest.NewRequest(http.MethodGet, "http://www.test.com/", http.NoBody)
+	req = req.WithContext(
+		context.WithValue(
+			req.Context(),
+			accesslog.DataTableKey,
+			&accesslog.LogData{Core: accesslog.CoreLogData{}},
+		),
+	)
+
+	next := http.HandlerFunc(func(rw http.ResponseWriter, _ *http.Request) {})
+
+	tracer := &mockTracer{}
+
+	handler := newEntryPoint(context.Background(), tracing.NewTracer(tracer, []string{}, []string{}, []string{}), nil, "test", next)
+	handler.ServeHTTP(httptest.NewRecorder(), req)
+
+	expectedSpanCtx := tracer.spans[0].SpanContext()
+
+	logData := accesslog.GetLogData(req)
+	assert.Equal(t, expectedSpanCtx.TraceID().String(), logData.Core[accesslog.TraceID])
+	assert.Equal(t, expectedSpanCtx.SpanID().String(), logData.Core[accesslog.SpanID])
+}