generic ephemeral volume: simpler metrics

A CounterVector with status as label may create unnecessary overhead
and using the success case with the empty label value wasn't
easy. It's better to have two seperate counters, one for total number
of calls and one for failed calls.

pkg/controller/volume/ephemeral/metrics/metrics.go

@@ -27,20 +27,24 @@ import (
 const EphemeralVolumeSubsystem = "ephemeral_volume_controller"
 
 var (
-	// EphemeralVolumeCreate tracks the number of
-	// PersistentVolumeClaims().Create calls for each failure
-	// reason
-	// (https://pkg.go.dev/k8s.io/apimachinery@v0.20.2/pkg/apis/meta/v1#StatusReason),
-	// with empty for successful calls.
-	EphemeralVolumeCreate = metrics.NewCounterVec(
+	// EphemeralVolumeCreateAttempts tracks the number of
+	// PersistentVolumeClaims().Create calls (both successful and unsuccessful)
+	EphemeralVolumeCreateAttempts = metrics.NewCounter(
 		&metrics.CounterOpts{
 			Subsystem:      EphemeralVolumeSubsystem,
-			Name:           "create",
+			Name:           "create_total",
 			Help:           "Number of PersistenVolumeClaims creation requests",
 			StabilityLevel: metrics.ALPHA,
-		},
-		[]string{"reason"},
-	)
+		})
+	// EphemeralVolumeCreateFailures tracks the number of unsuccessful
+	// PersistentVolumeClaims().Create calls
+	EphemeralVolumeCreateFailures = metrics.NewCounter(
+		&metrics.CounterOpts{
+			Subsystem:      EphemeralVolumeSubsystem,
+			Name:           "create_failures_total",
+			Help:           "Number of PersistenVolumeClaims creation requests",
+			StabilityLevel: metrics.ALPHA,
+		})
 )
 
 var registerMetrics sync.Once
@@ -48,6 +52,7 @@ var registerMetrics sync.Once
 // RegisterMetrics registers EphemeralVolume metrics.
 func RegisterMetrics() {
 	registerMetrics.Do(func() {
-		legacyregistry.MustRegister(EphemeralVolumeCreate)
+		legacyregistry.MustRegister(EphemeralVolumeCreateAttempts)
+		legacyregistry.MustRegister(EphemeralVolumeCreateFailures)
 	})
 }