core: add cluster label to all servicemonitor scraped metrics

Signed-off-by: Joshua Hoblitt <josh@hoblitt.com>

pkg/operator/k8sutil/prometheus.go

@@ -27,6 +27,7 @@ import (
 	"github.com/rook/rook/pkg/clusterd"
 	kerrors "k8s.io/apimachinery/pkg/api/errors"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/utils/ptr"
 )
 
 func getMonitoringClient(context *clusterd.Context) (*monitoringclient.Clientset, error) {
@@ -65,6 +66,10 @@ func GetServiceMonitor(name string, namespace string, portName string) *monitori
 					Path:        "/metrics",
 					Interval:    "10s",
 					HonorLabels: true,
+					RelabelConfigs: []monitoringv1.RelabelConfig{{
+						TargetLabel: "cluster",
+						Replacement: ptr.To(namespace),
+					}},
 				},
 			},
 		},

pkg/operator/k8sutil/prometheus_test.go

@@ -38,4 +38,6 @@ func TestGetServiceMonitor(t *testing.T) {
 	assert.NotNil(t, servicemonitor.Spec.NamespaceSelector.MatchNames)
 	assert.NotNil(t, servicemonitor.Spec.Selector.MatchLabels)
 	assert.NotNil(t, servicemonitor.Spec.Endpoints)
+	assert.Equal(t, "cluster", servicemonitor.Spec.Endpoints[0].RelabelConfigs[0].TargetLabel)
+	assert.Equal(t, namespace, *servicemonitor.Spec.Endpoints[0].RelabelConfigs[0].Replacement)
 }