feat: Add access mode metric for PersistentVolumes

Expose a kube_persistentvolume_access_mode metric that mirrors the
existing PVC access mode metric. This allows consumers to filter and
aggregate PersistentVolumes by access mode directly, without having to
scrape kube_persistentvolumeclaim_access_mode.

Using a small set of access-mode labels keeps cardinality low while
still allowing PV metrics to be sliced by access mode.

Signed-off-by: vvoeroes <virag.voeroes@inovex.de>

Author: viragvoros

docs/metrics/storage/persistentvolume-metrics.md

@@ -12,6 +12,7 @@
 | kube_persistentvolume_deletion_timestamp | Gauge       | Unix deletion timestamp                                                                                                   | seconds                 | `persistentvolume`=&lt;persistentvolume-name&gt; <br>                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | EXPERIMENTAL |
 | kube_persistentvolume_csi_attributes     | Gauge       | CSI attributes of the Persistent Volume, disabled by default, manage with [--metric-opt-in-list](../../developer/cli-arguments.md))     |                         | `persistentvolume`=&lt;persistentvolume-name&gt; <br> `csi_mounter`=&lt;csi-mounter&gt; <br> `csi_map_options`=&lt;csi-map-options&gt;                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | EXPERIMENTAL |
 | kube_persistentvolume_volume_mode       | Gauge       | Volume Mode information for the PersistentVolume.                                                                          |                         | `persistentvolume`=&lt;persistentvolume-name&gt; <br>`volumemode`=&lt;volumemode&gt;                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | EXPERIMENTAL       |
+| kube_persistentvolume_access_mode | Gauge | Access modes of the PersistentVolume. Only the four official access modes are emitted.           |                         | `persistentvolume`=&lt;persistentvolume-name&gt; <br>`accessmode`=<ReadWriteOnce \| ReadOnlyMany \| ReadWriteMany \| ReadWriteOncePod> | STABLE       |
 
 ## Useful metrics queries
 

internal/store/persistentvolume.go

@@ -59,6 +59,7 @@ func persistentVolumeMetricFamilies(allowAnnotationsList, allowLabelsList []stri
 		createPersistentVolumeDeletionTimestamp(),
 		createPersistentVolumeCSIAttributes(),
 		createPersistentVolumeMode(),
+		createPersistentVolumeAccessMode(),
 	}
 }
 
@@ -485,3 +486,27 @@ func createPersistentVolumeMode() generator.FamilyGenerator {
 		}),
 	)
 }
+
+func createPersistentVolumeAccessMode() generator.FamilyGenerator {
+	return *generator.NewFamilyGeneratorWithStability(
+		"kube_persistentvolume_access_mode",
+		"The access mode(s) specified by the persistent volume.",
+		metric.Gauge,
+		basemetrics.STABLE,
+		"",
+		wrapPersistentVolumeFunc(func(p *v1.PersistentVolume) *metric.Family {
+			ms := make([]*metric.Metric, 0, len(p.Spec.AccessModes))
+			for _, am := range p.Spec.AccessModes {
+				ms = append(ms, &metric.Metric{
+					LabelKeys:   []string{"access_mode"},
+					LabelValues: []string{string(am)},
+					Value:       1,
+				})
+			}
+
+			return &metric.Family{
+				Metrics: ms,
+			}
+		}),
+	)
+}

internal/store/persistentvolume_test.go

@@ -780,6 +780,26 @@ func TestPersistentVolumeStore(t *testing.T) {
 				`,
 			MetricNames: []string{"kube_persistentvolume_volume_mode"},
 		},
+		{
+			Obj: &v1.PersistentVolume{
+				ObjectMeta: metav1.ObjectMeta{
+					Name: "test-pv-access-modes",
+				},
+				Spec: v1.PersistentVolumeSpec{
+					AccessModes: []v1.PersistentVolumeAccessMode{
+						v1.ReadWriteOnce,
+						v1.ReadOnlyMany,
+					},
+				},
+			},
+			Want: `
+					# HELP kube_persistentvolume_access_mode [STABLE] The access mode(s) specified by the persistent volume.
+					# TYPE kube_persistentvolume_access_mode gauge
+					kube_persistentvolume_access_mode{persistentvolume="test-pv-access-modes",access_mode="ReadWriteOnce"} 1
+					kube_persistentvolume_access_mode{persistentvolume="test-pv-access-modes",access_mode="ReadOnlyMany"} 1
+				`,
+			MetricNames: []string{"kube_persistentvolume_access_mode"},
+		},
 	}
 	for i, c := range cases {
 		c.Func = generator.ComposeMetricGenFuncs(persistentVolumeMetricFamilies(c.AllowAnnotationsList, c.AllowLabelsList))