pkg/listwatcher: Fix multiListerWatcher to proceed on individual list…

…er errors

The multiListerWatcher is a composite object encapsulating multiple
ListerWatchers and implements the ListerWatcher interface.
When calling the List method on the multiListerWatcher, if an individual
Lister call fails, the outcome is treated as an error and the entire
call fails. This leads to KSM not exporting any metrics when it does not
have the necessary permissions for resources in one more more namespaces.

This commit modifies the multiListerWatcher List function to log errors
from individual ListerWatchers and continue with execution. As a result,
when KSM does not have permissions to list resources from
a namespace, it will still export metrics from namespaces it has
permissions to.

Fixes kubernetes#1413

Signed-off-by: fpetkovski <filip.petkovsky@gmail.com>

pkg/listwatch/listwatch.go

@@ -22,6 +22,8 @@ import (
 	"strings"
 	"sync"
 
+	"k8s.io/klog/v2"
+
 	v1 "k8s.io/api/core/v1"
 	"k8s.io/apimachinery/pkg/api/meta"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -135,24 +137,27 @@ type multiListerWatcher []cache.ListerWatcher
 // a single result.
 func (mlw multiListerWatcher) List(options metav1.ListOptions) (runtime.Object, error) {
 	l := metav1.List{}
-	var resourceVersions []string
-	for _, lw := range mlw {
+	resourceVersions := make([]string, len(mlw))
+	for i, lw := range mlw {
 		list, err := lw.List(options)
 		if err != nil {
-			return nil, err
+			klog.Errorf("Failed to list resources: %v", err)
+			continue
 		}
 		items, err := meta.ExtractList(list)
 		if err != nil {
-			return nil, err
+			klog.Errorf("Failed to extract list: %v", err)
+			continue
 		}
 		metaObj, err := meta.ListAccessor(list)
 		if err != nil {
-			return nil, err
+			klog.Errorf("Failed to list accessor: %v", err)
+			continue
 		}
 		for _, item := range items {
 			l.Items = append(l.Items, runtime.RawExtension{Object: item.DeepCopyObject()})
 		}
-		resourceVersions = append(resourceVersions, metaObj.GetResourceVersion())
+		resourceVersions[i] = metaObj.GetResourceVersion()
 	}
 	// Combine the resource versions so that the composite Watch method can
 	// distribute appropriate versions to each underlying Watch func.

pkg/listwatch/listwatch_test.go

@@ -0,0 +1,93 @@
+/*
+Copyright 2019 The Kubernetes Authors All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package listwatch_test
+
+import (
+	"fmt"
+	"testing"
+
+	v1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/watch"
+	"k8s.io/client-go/tools/cache"
+	"k8s.io/kube-state-metrics/v2/pkg/listwatch"
+)
+
+var errList = fmt.Errorf("error listing resources")
+
+type listWatcherStub struct {
+	err error
+}
+
+func (l listWatcherStub) List(_ metav1.ListOptions) (runtime.Object, error) {
+	if l.err != nil {
+		return nil, l.err
+	}
+
+	return makePodList(), nil
+}
+
+func (l listWatcherStub) Watch(_ metav1.ListOptions) (watch.Interface, error) {
+	return nil, nil
+}
+
+func TestMultiNamespaceListerWatcher(t *testing.T) {
+	namespaces := []string{"ns-succeed", "ns-fail", "ns-succeed"}
+	mlw := listwatch.MultiNamespaceListerWatcher(namespaces, []string{}, func(s string) cache.ListerWatcher {
+		if s == "ns-fail" {
+			return listWatcherStub{err: errList}
+		} else {
+			return listWatcherStub{}
+		}
+	})
+
+	result, err := mlw.List(metav1.ListOptions{})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	list, ok := result.(*metav1.List)
+	if !ok {
+		t.Fatal("invalid result type: want meta.List")
+	}
+	if len(list.Items) != 2 {
+		t.Fatalf("invalid item count: got %d, want %d", len(list.Items), 1)
+	}
+	if list.ResourceVersion != "1//1" {
+		t.Fatalf("invalid resource version: got %s, want %s", list.ResourceVersion, "/1")
+	}
+}
+
+func makePodList() *v1.PodList {
+	return &v1.PodList{
+		TypeMeta: metav1.TypeMeta{
+			Kind:       "pods",
+			APIVersion: "",
+		},
+		ListMeta: metav1.ListMeta{
+			ResourceVersion: "1",
+		},
+		Items: []v1.Pod{
+			{
+				ObjectMeta: metav1.ObjectMeta{
+					Name: "test-pod",
+				},
+			},
+		},
+	}
+}