feat: add proxy error metric (#3470)

Signed-off-by: Jim Ma <majinjing3@gmail.com>

client/daemon/metrics/metrics.go

@@ -60,6 +60,13 @@ var (
 		Help:      "Counter of the total proxy request via Dragonfly.",
 	})
 
+	ProxyErrorRequestViaDragonflyCount = promauto.NewCounter(prometheus.CounterOpts{
+		Namespace: types.MetricsNamespace,
+		Subsystem: types.DfdaemonMetricsName,
+		Name:      "proxy_error_request_via_dragonfly_total",
+		Help:      "Counter of the total error proxy request via Dragonfly.",
+	})
+
 	ProxyRequestNotViaDragonflyCount = promauto.NewCounter(prometheus.CounterOpts{
 		Namespace: types.MetricsNamespace,
 		Subsystem: types.DfdaemonMetricsName,

client/daemon/transport/transport.go

@@ -229,30 +229,23 @@ func New(options ...Option) http.RoundTripper {
 // RoundTrip only process first redirect at present
 func (rt *transport) RoundTrip(req *http.Request) (resp *http.Response, err error) {
 	if rt.shouldUseDragonfly(req) {
-		// delete the Accept-Encoding header to avoid returning the same cached
-		// result for different requests
-		req.Header.Del("Accept-Encoding")
-
-		ctx := req.Context()
-		if req.URL.Scheme == "https" {
-			// for https, the trace info is in request header
-			ctx = traceContext.Extract(req.Context(), propagation.HeaderCarrier(req.Header))
+		resp, err = rt.roundTripWithDragonfly(req)
+		if err != nil {
+			metrics.ProxyErrorRequestViaDragonflyCount.Add(1)
+			logger.With("method", req.Method, "url", req.URL.String()).Errorf("round trip with dragonfly error: %s", err)
+			return resp, err
 		}
-
-		logger.Debugf("round trip with dragonfly: %s", req.URL.String())
-		metrics.ProxyRequestViaDragonflyCount.Add(1)
-		resp, err = rt.download(ctx, req)
 	} else {
 		logger.Debugf("round trip directly, method: %s, url: %s", req.Method, req.URL.String())
 		req.Host = req.URL.Host
 		req.Header.Set("Host", req.Host)
 		metrics.ProxyRequestNotViaDragonflyCount.Add(1)
 		resp, err = rt.baseRoundTripper.RoundTrip(req)
-	}
 
-	if err != nil {
-		logger.With("method", req.Method, "url", req.URL.String()).Errorf("round trip error: %s", err)
-		return resp, err
+		if err != nil {
+			logger.With("method", req.Method, "url", req.URL.String()).Errorf("round trip directly error: %s", err)
+			return resp, err
+		}
 	}
 
 	if resp.ContentLength > 0 {
@@ -263,6 +256,22 @@ func (rt *transport) RoundTrip(req *http.Request) (resp *http.Response, err erro
 	return resp, err
 }
 
+func (rt *transport) roundTripWithDragonfly(req *http.Request) (*http.Response, error) {
+	// delete the Accept-Encoding header to avoid returning the same cached
+	// result for different requests
+	req.Header.Del("Accept-Encoding")
+
+	ctx := req.Context()
+	if req.URL.Scheme == "https" {
+		// for https, the trace info is in request header
+		ctx = traceContext.Extract(req.Context(), propagation.HeaderCarrier(req.Header))
+	}
+
+	logger.Debugf("round trip with dragonfly: %s", req.URL.String())
+	metrics.ProxyRequestViaDragonflyCount.Add(1)
+	return rt.download(ctx, req)
+}
+
 // NeedUseDragonfly is the default value for shouldUseDragonfly, which downloads all
 // images layers with dragonfly.
 func NeedUseDragonfly(req *http.Request) bool {