apiserver/etcd3: fix segv during metric collection

Fix a segfault when collecting the storage size metrics when the getters
used to collect the data on etcd haven't been initialized properly. This
happens when the EtcdOptions are not applied which is the case for
aggregated apiservers that don't care about storage.

Signed-off-by: Damien Grisonnet <dgrisonn@redhat.com>

staging/src/k8s.io/apiserver/pkg/storage/etcd3/metrics/metrics.go

@@ -85,7 +85,7 @@ var (
 		[]string{"endpoint"},
 	)
 	storageSizeDescription   = compbasemetrics.NewDesc("apiserver_storage_size_bytes", "Size of the storage database file physically allocated in bytes.", []string{"cluster"}, nil, compbasemetrics.ALPHA, "")
-	storageMonitor           = &monitorCollector{}
+	storageMonitor           = &monitorCollector{monitorGetter: func() ([]Monitor, error) { return nil, nil }}
 	etcdEventsReceivedCounts = compbasemetrics.NewCounterVec(
 		&compbasemetrics.CounterOpts{
 			Subsystem:      "apiserver",

staging/src/k8s.io/apiserver/pkg/storage/etcd3/metrics/metrics_test.go

@@ -17,6 +17,7 @@ limitations under the License.
 package metrics
 
 import (
+	"context"
 	"errors"
 	"strings"
 	"testing"
@@ -179,3 +180,60 @@ etcd_request_errors_total{operation="foo",type="bar"} 1
 		})
 	}
 }
+
+func TestStorageSizeCollector(t *testing.T) {
+	registry := metrics.NewKubeRegistry()
+	registry.CustomMustRegister(storageMonitor)
+
+	testCases := []struct {
+		desc           string
+		getterOverride func() ([]Monitor, error)
+		err            error
+		want           string
+	}{
+		{
+			desc: "fake etcd getter",
+			getterOverride: func() ([]Monitor, error) {
+				return []Monitor{fakeEtcdMonitor{storageSize: 1e9}}, nil
+			},
+			err: nil,
+			want: `# HELP apiserver_storage_size_bytes [ALPHA] Size of the storage database file physically allocated in bytes.
+			# TYPE apiserver_storage_size_bytes gauge
+			apiserver_storage_size_bytes{cluster="etcd-0"} 1e+09
+			`,
+		},
+		{
+			desc:           "getters not configured",
+			getterOverride: nil,
+			err:            nil,
+			want:           ``,
+		},
+	}
+
+	for _, test := range testCases {
+		t.Run(test.desc, func(t *testing.T) {
+			defer registry.Reset()
+			if test.getterOverride != nil {
+				oldGetter := storageMonitor.monitorGetter
+				defer SetStorageMonitorGetter(oldGetter)
+				SetStorageMonitorGetter(test.getterOverride)
+			}
+			if err := testutil.GatherAndCompare(registry, strings.NewReader(test.want), "apiserver_storage_size_bytes"); err != nil {
+				t.Fatal(err)
+			}
+		})
+	}
+
+}
+
+type fakeEtcdMonitor struct {
+	storageSize int64
+}
+
+func (m fakeEtcdMonitor) Monitor(_ context.Context) (StorageMetrics, error) {
+	return StorageMetrics{Size: m.storageSize}, nil
+}
+
+func (m fakeEtcdMonitor) Close() error {
+	return nil
+}