Adding extra metric till now, not impacting path

pkg/client/metrics/metrics.go

@@ -18,11 +18,16 @@ package metrics
 
 import (
 	"context"
+	"net/http"
 	"net/url"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
 
+	apimetrics "k8s.io/apiserver/pkg/endpoints/metrics"
+	"k8s.io/component-base/metrics"
+	"k8s.io/component-base/metrics/legacyregistry"
+
 	"sigs.k8s.io/prometheus-adapter/pkg/client"
 )
 
@@ -30,18 +35,47 @@ var (
 	// queryLatency is the total latency of any query going through the
 	// various endpoints (query, range-query, series).  It includes some deserialization
 	// overhead and HTTP overhead.
-	queryLatency = prometheus.NewHistogramVec(
-		prometheus.HistogramOpts{
-			Name:    "cmgateway_prometheus_query_latency_seconds",
-			Help:    "Prometheus client query latency in seconds.  Broken down by target prometheus endpoint and target server",
-			Buckets: prometheus.ExponentialBuckets(0.0001, 2, 10),
+	queryLatency = metrics.NewHistogramVec(
+		&metrics.HistogramOpts{
+			Namespace: "prometheus_adapter",
+			Subsystem: "prometheus_client",
+			Name:      "request_duration_seconds",
+			Help:      "Prometheus client query latency in seconds.  Broken down by target prometheus endpoint and target server",
+			Buckets:   prometheus.DefBuckets,
 		},
-		[]string{"endpoint", "server"},
+		[]string{"path", "server"},
 	)
+
+	// define a counter for API errors for various ErrorTypes
+    apiErrorCount = metrics.NewCounterVec(
+    	&metrics.CounterOpts{
+    		Namespace: "prometheus_adapter",
+    		Subsystem: "prometheus_client",
+    		Name:      "api_errors_total",
+    		Help:      "Total number of API errors",
+    	},
+    	[]string{"error_code", "path", "server"},
+    )
 )
 
-func init() {
-	prometheus.MustRegister(queryLatency)
+func MetricsHandler() (http.HandlerFunc, error) {
+	registry := metrics.NewKubeRegistry()
+
+	errRegisterQueryLatency := registry.Register(queryLatency)
+	if errRegisterQueryLatency != nil {
+		return nil, errRegisterQueryLatency
+	}
+
+	errRegisterAPIErrorCount := registry.Register(apiErrorCount)
+    if errRegisterAPIErrorCount != nil {
+        return nil, errRegisterAPIErrorCount
+    }
+
+	apimetrics.Register()
+	return func(w http.ResponseWriter, req *http.Request) {
+		legacyregistry.Handler().ServeHTTP(w, req)
+		metrics.HandlerFor(registry, metrics.HandlerOpts{}).ServeHTTP(w, req)
+	}, nil
 }
 
 // instrumentedClient is a client.GenericAPIClient which instruments calls to Do,
@@ -58,12 +92,16 @@ func (c *instrumentedGenericClient) Do(ctx context.Context, verb, endpoint strin
 		endTime := time.Now()
 		// skip calls where we don't make the actual request
 		if err != nil {
-			if _, wasAPIErr := err.(*client.Error); !wasAPIErr {
-				// TODO: measure API errors by code?
-				return
-			}
+			if apiErr, wasAPIErr := err.(*client.Error); wasAPIErr {
+				// Measure API errors
+                apiErrorCount.With(prometheus.Labels{"error_code": string(apiErr.Type), "path": endpoint, "server": c.serverName}).Inc()
+			} else {
+                // Increment a generic error code counter
+                apiErrorCount.With(prometheus.Labels{"error_code": "generic", "path": endpoint, "server": c.serverName}).Inc()
+             }
+			return
 		}
-		queryLatency.With(prometheus.Labels{"endpoint": endpoint, "server": c.serverName}).Observe(endTime.Sub(startTime).Seconds())
+		queryLatency.With(prometheus.Labels{"path": endpoint, "server": c.serverName}).Observe(endTime.Sub(startTime).Seconds())
 	}()
 
 	var resp client.APIResponse
@@ -76,4 +114,4 @@ func InstrumentGenericAPIClient(client client.GenericAPIClient, serverName strin
 		serverName: serverName,
 		client:     client,
 	}
-}
+}