kubectl/drain add support for custom pod filters

Currently, there is no way to supply custom pod filters to
exclude pods meeting arbitrary criteria when using drain
as a library.

This commit adds the ability for developers to add custom
filters to the drain operation when utilizing drain
as a library.

This commit exports certain types that were previously
private to allow for better code reuse.

This commit also adds appropriate unit tests.

Author: michaelgugino

staging/src/k8s.io/kubectl/pkg/drain/drain.go

@@ -65,6 +65,11 @@ type Helper struct {
 	// won't drain otherwise
 	SkipWaitForDeleteTimeoutSeconds int
 
+	// AdditionalFilters are applied sequentially after base drain filters to
+	// exclude pods using custom logic.  Any filter that returns PodDeleteStatus
+	// with Delete == false will immediately stop execution of further filters.
+	AdditionalFilters []PodFilter
+
 	Out    io.Writer
 	ErrOut io.Writer
 
@@ -169,7 +174,7 @@ func (d *Helper) EvictPod(pod corev1.Pod, policyGroupVersion string) error {
 // or error if it cannot list pods. All pods that are ready to be deleted can be obtained with .Pods(),
 // and string with all warning can be obtained with .Warnings(), and .Errors() for all errors that
 // occurred during deletion.
-func (d *Helper) GetPodsForDeletion(nodeName string) (*podDeleteList, []error) {
+func (d *Helper) GetPodsForDeletion(nodeName string) (*PodDeleteList, []error) {
 	labelSelector, err := labels.Parse(d.PodSelector)
 	if err != nil {
 		return nil, []error{err}
@@ -182,35 +187,37 @@ func (d *Helper) GetPodsForDeletion(nodeName string) (*podDeleteList, []error) {
 		return nil, []error{err}
 	}
 
-	pods := []podDelete{}
+	list := filterPods(podList, d.makeFilters())
+	if errs := list.errors(); len(errs) > 0 {
+		return list, errs
+	}
+
+	return list, nil
+}
 
+func filterPods(podList *corev1.PodList, filters []PodFilter) *PodDeleteList {
+	pods := []PodDelete{}
 	for _, pod := range podList.Items {
-		var status podDeleteStatus
-		for _, filter := range d.makeFilters() {
+		var status PodDeleteStatus
+		for _, filter := range filters {
 			status = filter(pod)
-			if !status.delete {
+			if !status.Delete {
 				// short-circuit as soon as pod is filtered out
 				// at that point, there is no reason to run pod
 				// through any additional filters
 				break
 			}
 		}
-		// Add the pod to podDeleteList no matter what podDeleteStatus is,
-		// those pods whose podDeleteStatus is false like DaemonSet will
+		// Add the pod to PodDeleteList no matter what PodDeleteStatus is,
+		// those pods whose PodDeleteStatus is false like DaemonSet will
 		// be catched by list.errors()
-		pods = append(pods, podDelete{
-			pod:    pod,
-			status: status,
+		pods = append(pods, PodDelete{
+			Pod:    pod,
+			Status: status,
 		})
 	}
-
-	list := &podDeleteList{items: pods}
-
-	if errs := list.errors(); len(errs) > 0 {
-		return list, errs
-	}
-
-	return list, nil
+	list := &PodDeleteList{items: pods}
+	return list
 }
 
 // DeleteOrEvictPods deletes or evicts the pods on the api server

staging/src/k8s.io/kubectl/pkg/drain/drain_test.go

@@ -389,3 +389,72 @@ func TestDeleteOrEvict(t *testing.T) {
 		})
 	}
 }
+
+func mockFilterSkip(_ corev1.Pod) PodDeleteStatus {
+	return MakePodDeleteStatusSkip()
+}
+
+func mockFilterOkay(_ corev1.Pod) PodDeleteStatus {
+	return MakePodDeleteStatusOkay()
+}
+
+func TestFilterPods(t *testing.T) {
+	tCases := []struct {
+		description        string
+		expectedPodListLen int
+		additionalFilters  []PodFilter
+	}{
+		{
+			description:        "AdditionalFilter skip all",
+			expectedPodListLen: 0,
+			additionalFilters: []PodFilter{
+				mockFilterSkip,
+				mockFilterOkay,
+			},
+		},
+		{
+			description:        "AdditionalFilter okay all",
+			expectedPodListLen: 1,
+			additionalFilters: []PodFilter{
+				mockFilterOkay,
+			},
+		},
+		{
+			description:        "AdditionalFilter Skip after Okay all skip",
+			expectedPodListLen: 0,
+			additionalFilters: []PodFilter{
+				mockFilterOkay,
+				mockFilterSkip,
+			},
+		},
+		{
+			description:        "No additionalFilters okay all",
+			expectedPodListLen: 1,
+		},
+	}
+	for _, tc := range tCases {
+		t.Run(tc.description, func(t *testing.T) {
+			h := &Helper{
+				Force:             true,
+				AdditionalFilters: tc.additionalFilters,
+			}
+			pod := corev1.Pod{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "pod",
+					Namespace: "default",
+				},
+			}
+			podList := corev1.PodList{
+				Items: []corev1.Pod{
+					pod,
+				},
+			}
+
+			list := filterPods(&podList, h.makeFilters())
+			podsLen := len(list.Pods())
+			if podsLen != tc.expectedPodListLen {
+				t.Errorf("%s: unexpected evictions; actual %v; expected %v", tc.description, podsLen, tc.expectedPodListLen)
+			}
+		})
+	}
+}

staging/src/k8s.io/kubectl/pkg/drain/filter_test.go

@@ -63,8 +63,8 @@ func TestSkipDeletedFilter(t *testing.T) {
 		}
 
 		podDeleteStatus := h.skipDeletedFilter(pod)
-		if podDeleteStatus.delete != tc.expectedDelete {
-			t.Errorf("test %v: unexpected podDeleteStatus.delete; actual %v; expected %v", i, podDeleteStatus.delete, tc.expectedDelete)
+		if podDeleteStatus.Delete != tc.expectedDelete {
+			t.Errorf("test %v: unexpected podDeleteStatus.delete; actual %v; expected %v", i, podDeleteStatus.Delete, tc.expectedDelete)
 		}
 	}
 }