Configure ErrorLog in httputil.ReverseProxy

pkg/server/service/proxy.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	stdlog "log"
 	"net"
 	"net/http"
 	"net/http/httputil"
@@ -12,6 +13,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/sirupsen/logrus"
 	ptypes "github.com/traefik/paerser/types"
 	"github.com/traefik/traefik/v2/pkg/config/dynamic"
 	"github.com/traefik/traefik/v2/pkg/log"
@@ -81,6 +83,7 @@ func buildProxy(passHostHeader *bool, responseForwarding *dynamic.ResponseForwar
 		Transport:     roundTripper,
 		FlushInterval: time.Duration(flushInterval),
 		BufferPool:    bufferPool,
+		ErrorLog:      stdlog.New(log.WithoutContext().WriterLevel(logrus.DebugLevel), "", 0),
 		ErrorHandler: func(w http.ResponseWriter, request *http.Request, err error) {
 			statusCode := http.StatusInternalServerError