feat: add annotation to ignore local storage volume during scale down

- this is so that scale down is not blocked on local storage volume
- for pods where it is okay to ignore local storage volume
Signed-off-by: vadasambar <surajrbanakar@gmail.com>

fix: tests failing
- there was a problem in the logic
Signed-off-by: vadasambar <surajrbanakar@gmail.com>

test: add unit test for `IgnoreLocalStorageVolumeKey`
Signed-off-by: vadasambar <surajrbanakar@gmail.com>

refactor: use `IgnoreLocalStorageVolumeKey`  in tests instead of hardcoding the annotation
Signed-off-by: vadasambar <surajrbanakar@gmail.com>

fix: wording for test name
- `pod with EmptyDir but IgnoreLocalStorageVolumeKey annotation` -> `pod with EmptyDir and IgnoreLocalStorageVolumeKey annotation`
Signed-off-by: vadasambar <surajrbanakar@gmail.com>

fix: simulator drain tests failing
- set local storage vol name (required)
Signed-off-by: vadasambar <surajrbanakar@gmail.com>

refactor: add support for multiple vals in `safe-to-evict-local-volume` annotation
- add more unit tests
Signed-off-by: vadasambar <surajrbanakar@gmail.com>

refactor: rename ignore local vol key `safe-to-evict-local-volume` -> `safe-to-evict-local-volumes`
- abtract code to process annotation into a separate fn
- shorten name for test cases
Signed-off-by: vadasambar <surajrbanakar@gmail.com>

docs: update FAQ with info about `safe-to-evict-local-volumes` annotation
Signed-off-by: vadasambar <surajrbanakar@gmail.com>

docs: add the FAQ for `safe-to-evict-local-volumes` annotation
Signed-off-by: vadasambar <surajrbanakar@gmail.com>

docs: fix formatting for `safe-to-evict-local-volumes` in FAQ
Signed-off-by: vadasambar <surajrbanakar@gmail.com>

docs: format the `safe-to-evict-local-volumes` as a bullet
Signed-off-by: vadasambar <surajrbanakar@gmail.com>

docs: fix `Unless` -> `unless` to make it consistent with other lines
Signed-off-by: vadasambar <surajrbanakar@gmail.com>

test: add an extra test for mismatching local vol value in annotation
Signed-off-by: vadasambar <surajrbanakar@gmail.com>

docs: make the wording clearer
- for `safe-to-evict-local-volumes` annotation
Signed-off-by: vadasambar <surajrbanakar@gmail.com>

cluster-autoscaler/FAQ.md

@@ -88,7 +88,12 @@ Cluster Autoscaler decreases the size of the cluster when some nodes are consist
   * are not run on the node by default, *
   * don't have a [pod disruption budget](https://kubernetes.io/docs/concepts/workloads/pods/disruptions/#how-disruption-budgets-work) set or their PDB is too restrictive (since CA 0.6).
 * Pods that are not backed by a controller object (so not created by deployment, replica set, job, stateful set etc). *
-* Pods with local storage. *
+* Pods with local storage. *  
+    - unless the pod has the following annotation set:
+      ```
+      "cluster-autoscaler.kubernetes.io/safe-to-evict-local-volumes": "volume-1,volume-2,.."
+      ```
+      and all of the pod's local volumes are listed in the annotation value.
 * Pods that cannot be moved elsewhere due to various constraints (lack of resources, non-matching node selectors or affinity,
 matching anti-affinity, etc)
 * Pods that have the following annotation set:

cluster-autoscaler/simulator/drain_test.go

@@ -115,6 +115,7 @@ func TestGetPodsToMove(t *testing.T) {
 		Spec: apiv1.PodSpec{
 			Volumes: []apiv1.Volume{
 				{
+					Name: "empty-vol",
 					VolumeSource: apiv1.VolumeSource{
 						EmptyDir: &apiv1.EmptyDirVolumeSource{},
 					},
@@ -136,6 +137,7 @@ func TestGetPodsToMove(t *testing.T) {
 		Spec: apiv1.PodSpec{
 			Volumes: []apiv1.Volume{
 				{
+					Name: "my-repo",
 					VolumeSource: apiv1.VolumeSource{
 						GitRepo: &apiv1.GitRepoVolumeSource{
 							Repository: "my-repo",

cluster-autoscaler/utils/drain/drain.go

@@ -18,6 +18,7 @@ package drain
 
 import (
 	"fmt"
+	"strings"
 	"time"
 
 	apiv1 "k8s.io/api/core/v1"
@@ -38,6 +39,8 @@ const (
 	// PodSafeToEvictKey - annotation that ignores constraints to evict a pod like not being replicated, being on
 	// kube-system namespace or having a local storage.
 	PodSafeToEvictKey = "cluster-autoscaler.kubernetes.io/safe-to-evict"
+	// SafeToEvictLocalVolumesKey - annotation that ignores (doesn't block on) a local storage volume during node scale down
+	SafeToEvictLocalVolumesKey = "cluster-autoscaler.kubernetes.io/safe-to-evict-local-volumes"
 )
 
 // BlockingPod represents a pod which is blocking the scale down of a node.
@@ -219,7 +222,7 @@ func GetPodsForDeletionOnNodeDrain(
 					return []*apiv1.Pod{}, []*apiv1.Pod{}, &BlockingPod{Pod: pod, Reason: UnmovableKubeSystemPod}, fmt.Errorf("non-daemonset, non-mirrored, non-pdb-assigned kube-system pod present: %s", pod.Name)
 				}
 			}
-			if HasLocalStorage(pod) && skipNodesWithLocalStorage {
+			if HasBlockingLocalStorage(pod) && skipNodesWithLocalStorage {
 				return []*apiv1.Pod{}, []*apiv1.Pod{}, &BlockingPod{Pod: pod, Reason: LocalStorageRequested}, fmt.Errorf("pod with local storage present: %s", pod.Name)
 			}
 			if hasNotSafeToEvictAnnotation(pod) {
@@ -250,16 +253,30 @@ func isPodTerminal(pod *apiv1.Pod) bool {
 	return pod.Status.Phase == apiv1.PodFailed
 }
 
-// HasLocalStorage returns true if pod has any local storage.
-func HasLocalStorage(pod *apiv1.Pod) bool {
+// HasBlockingLocalStorage returns true if pod has any local storage
+// without pod annotation `<SafeToEvictLocalVolumeKey>: <volume-name-1>,<volume-name-2>...`
+func HasBlockingLocalStorage(pod *apiv1.Pod) bool {
+	isNonBlocking := getNonBlockingVolumes(pod)
 	for _, volume := range pod.Spec.Volumes {
-		if isLocalVolume(&volume) {
+		if isLocalVolume(&volume) && !isNonBlocking[volume.Name] {
 			return true
 		}
 	}
 	return false
 }
 
+func getNonBlockingVolumes(pod *apiv1.Pod) map[string]bool {
+	isNonBlocking := map[string]bool{}
+	annotationVal := pod.GetAnnotations()[SafeToEvictLocalVolumesKey]
+	if annotationVal != "" {
+		vols := strings.Split(annotationVal, ",")
+		for _, v := range vols {
+			isNonBlocking[v] = true
+		}
+	}
+	return isNonBlocking
+}
+
 func isLocalVolume(volume *apiv1.Volume) bool {
 	return volume.HostPath != nil || volume.EmptyDir != nil
 }

cluster-autoscaler/utils/drain/drain_test.go

@@ -210,6 +210,178 @@ func TestDrain(t *testing.T) {
 		},
 	}
 
+	emptyDirSafeToEvictVolumeSingleVal := &apiv1.Pod{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:            "bar",
+			Namespace:       "default",
+			OwnerReferences: GenerateOwnerReferences(rc.Name, "ReplicationController", "core/v1", ""),
+			Annotations: map[string]string{
+				SafeToEvictLocalVolumesKey: "scratch",
+			},
+		},
+		Spec: apiv1.PodSpec{
+			NodeName: "node",
+			Volumes: []apiv1.Volume{
+				{
+					Name:         "scratch",
+					VolumeSource: apiv1.VolumeSource{EmptyDir: &apiv1.EmptyDirVolumeSource{Medium: ""}},
+				},
+			},
+		},
+	}
+
+	emptyDirSafeToEvictLocalVolumeSingleValEmpty := &apiv1.Pod{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:            "bar",
+			Namespace:       "default",
+			OwnerReferences: GenerateOwnerReferences(rc.Name, "ReplicationController", "core/v1", ""),
+			Annotations: map[string]string{
+				SafeToEvictLocalVolumesKey: "",
+			},
+		},
+		Spec: apiv1.PodSpec{
+			NodeName: "node",
+			Volumes: []apiv1.Volume{
+				{
+					Name:         "scratch",
+					VolumeSource: apiv1.VolumeSource{EmptyDir: &apiv1.EmptyDirVolumeSource{Medium: ""}},
+				},
+			},
+		},
+	}
+
+	emptyDirSafeToEvictLocalVolumeSingleValNonMatching := &apiv1.Pod{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:            "bar",
+			Namespace:       "default",
+			OwnerReferences: GenerateOwnerReferences(rc.Name, "ReplicationController", "core/v1", ""),
+			Annotations: map[string]string{
+				SafeToEvictLocalVolumesKey: "scratch-2",
+			},
+		},
+		Spec: apiv1.PodSpec{
+			NodeName: "node",
+			Volumes: []apiv1.Volume{
+				{
+					Name:         "scratch-1",
+					VolumeSource: apiv1.VolumeSource{EmptyDir: &apiv1.EmptyDirVolumeSource{Medium: ""}},
+				},
+			},
+		},
+	}
+
+	emptyDirSafeToEvictLocalVolumeMultiValAllMatching := &apiv1.Pod{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:            "bar",
+			Namespace:       "default",
+			OwnerReferences: GenerateOwnerReferences(rc.Name, "ReplicationController", "core/v1", ""),
+			Annotations: map[string]string{
+				SafeToEvictLocalVolumesKey: "scratch-1,scratch-2,scratch-3",
+			},
+		},
+		Spec: apiv1.PodSpec{
+			NodeName: "node",
+			Volumes: []apiv1.Volume{
+				{
+					Name:         "scratch-1",
+					VolumeSource: apiv1.VolumeSource{EmptyDir: &apiv1.EmptyDirVolumeSource{Medium: ""}},
+				},
+				{
+					Name:         "scratch-2",
+					VolumeSource: apiv1.VolumeSource{EmptyDir: &apiv1.EmptyDirVolumeSource{Medium: ""}},
+				},
+				{
+					Name:         "scratch-3",
+					VolumeSource: apiv1.VolumeSource{EmptyDir: &apiv1.EmptyDirVolumeSource{Medium: ""}},
+				},
+			},
+		},
+	}
+
+	emptyDirSafeToEvictLocalVolumeMultiValNonMatching := &apiv1.Pod{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:            "bar",
+			Namespace:       "default",
+			OwnerReferences: GenerateOwnerReferences(rc.Name, "ReplicationController", "core/v1", ""),
+			Annotations: map[string]string{
+				SafeToEvictLocalVolumesKey: "scratch-1,scratch-2,scratch-5",
+			},
+		},
+		Spec: apiv1.PodSpec{
+			NodeName: "node",
+			Volumes: []apiv1.Volume{
+				{
+					Name:         "scratch-1",
+					VolumeSource: apiv1.VolumeSource{EmptyDir: &apiv1.EmptyDirVolumeSource{Medium: ""}},
+				},
+				{
+					Name:         "scratch-2",
+					VolumeSource: apiv1.VolumeSource{EmptyDir: &apiv1.EmptyDirVolumeSource{Medium: ""}},
+				},
+				{
+					Name:         "scratch-3",
+					VolumeSource: apiv1.VolumeSource{EmptyDir: &apiv1.EmptyDirVolumeSource{Medium: ""}},
+				},
+			},
+		},
+	}
+
+	emptyDirSafeToEvictLocalVolumeMultiValSomeMatchingVals := &apiv1.Pod{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:            "bar",
+			Namespace:       "default",
+			OwnerReferences: GenerateOwnerReferences(rc.Name, "ReplicationController", "core/v1", ""),
+			Annotations: map[string]string{
+				SafeToEvictLocalVolumesKey: "scratch-1,scratch-2",
+			},
+		},
+		Spec: apiv1.PodSpec{
+			NodeName: "node",
+			Volumes: []apiv1.Volume{
+				{
+					Name:         "scratch-1",
+					VolumeSource: apiv1.VolumeSource{EmptyDir: &apiv1.EmptyDirVolumeSource{Medium: ""}},
+				},
+				{
+					Name:         "scratch-2",
+					VolumeSource: apiv1.VolumeSource{EmptyDir: &apiv1.EmptyDirVolumeSource{Medium: ""}},
+				},
+				{
+					Name:         "scratch-3",
+					VolumeSource: apiv1.VolumeSource{EmptyDir: &apiv1.EmptyDirVolumeSource{Medium: ""}},
+				},
+			},
+		},
+	}
+
+	emptyDirSafeToEvictLocalVolumeMultiValEmpty := &apiv1.Pod{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:            "bar",
+			Namespace:       "default",
+			OwnerReferences: GenerateOwnerReferences(rc.Name, "ReplicationController", "core/v1", ""),
+			Annotations: map[string]string{
+				SafeToEvictLocalVolumesKey: ",",
+			},
+		},
+		Spec: apiv1.PodSpec{
+			NodeName: "node",
+			Volumes: []apiv1.Volume{
+				{
+					Name:         "scratch-1",
+					VolumeSource: apiv1.VolumeSource{EmptyDir: &apiv1.EmptyDirVolumeSource{Medium: ""}},
+				},
+				{
+					Name:         "scratch-2",
+					VolumeSource: apiv1.VolumeSource{EmptyDir: &apiv1.EmptyDirVolumeSource{Medium: ""}},
+				},
+				{
+					Name:         "scratch-3",
+					VolumeSource: apiv1.VolumeSource{EmptyDir: &apiv1.EmptyDirVolumeSource{Medium: ""}},
+				},
+			},
+		},
+	}
+
 	terminalPod := &apiv1.Pod{
 		ObjectMeta: metav1.ObjectMeta{
 			Name:      "bar",
@@ -489,6 +661,76 @@ func TestDrain(t *testing.T) {
 			expectBlockingPod:   &BlockingPod{Pod: emptydirPod, Reason: LocalStorageRequested},
 			expectDaemonSetPods: []*apiv1.Pod{},
 		},
+		{
+			description:         "pod with EmptyDir and SafeToEvictLocalVolumesKey annotation",
+			pods:                []*apiv1.Pod{emptyDirSafeToEvictVolumeSingleVal},
+			pdbs:                []*policyv1.PodDisruptionBudget{},
+			rcs:                 []*apiv1.ReplicationController{&rc},
+			expectFatal:         false,
+			expectPods:          []*apiv1.Pod{emptyDirSafeToEvictVolumeSingleVal},
+			expectBlockingPod:   &BlockingPod{},
+			expectDaemonSetPods: []*apiv1.Pod{},
+		},
+		{
+			description:         "pod with EmptyDir and empty value for SafeToEvictLocalVolumesKey annotation",
+			pods:                []*apiv1.Pod{emptyDirSafeToEvictLocalVolumeSingleValEmpty},
+			pdbs:                []*policyv1.PodDisruptionBudget{},
+			rcs:                 []*apiv1.ReplicationController{&rc},
+			expectFatal:         true,
+			expectPods:          []*apiv1.Pod{},
+			expectBlockingPod:   &BlockingPod{Pod: emptyDirSafeToEvictLocalVolumeSingleValEmpty, Reason: LocalStorageRequested},
+			expectDaemonSetPods: []*apiv1.Pod{},
+		},
+		{
+			description:         "pod with EmptyDir and non-matching value for SafeToEvictLocalVolumesKey annotation",
+			pods:                []*apiv1.Pod{emptyDirSafeToEvictLocalVolumeSingleValNonMatching},
+			pdbs:                []*policyv1.PodDisruptionBudget{},
+			rcs:                 []*apiv1.ReplicationController{&rc},
+			expectFatal:         true,
+			expectPods:          []*apiv1.Pod{},
+			expectBlockingPod:   &BlockingPod{Pod: emptyDirSafeToEvictLocalVolumeSingleValNonMatching, Reason: LocalStorageRequested},
+			expectDaemonSetPods: []*apiv1.Pod{},
+		},
+		{
+			description:         "pod with EmptyDir and SafeToEvictLocalVolumesKey annotation with matching values",
+			pods:                []*apiv1.Pod{emptyDirSafeToEvictLocalVolumeMultiValAllMatching},
+			pdbs:                []*policyv1.PodDisruptionBudget{},
+			rcs:                 []*apiv1.ReplicationController{&rc},
+			expectFatal:         false,
+			expectPods:          []*apiv1.Pod{emptyDirSafeToEvictLocalVolumeMultiValAllMatching},
+			expectBlockingPod:   &BlockingPod{},
+			expectDaemonSetPods: []*apiv1.Pod{},
+		},
+		{
+			description:         "pod with EmptyDir and SafeToEvictLocalVolumesKey annotation with non-matching values",
+			pods:                []*apiv1.Pod{emptyDirSafeToEvictLocalVolumeMultiValNonMatching},
+			pdbs:                []*policyv1.PodDisruptionBudget{},
+			rcs:                 []*apiv1.ReplicationController{&rc},
+			expectFatal:         true,
+			expectPods:          []*apiv1.Pod{},
+			expectBlockingPod:   &BlockingPod{Pod: emptyDirSafeToEvictLocalVolumeMultiValNonMatching, Reason: LocalStorageRequested},
+			expectDaemonSetPods: []*apiv1.Pod{},
+		},
+		{
+			description:         "pod with EmptyDir and SafeToEvictLocalVolumesKey annotation with some matching values",
+			pods:                []*apiv1.Pod{emptyDirSafeToEvictLocalVolumeMultiValSomeMatchingVals},
+			pdbs:                []*policyv1.PodDisruptionBudget{},
+			rcs:                 []*apiv1.ReplicationController{&rc},
+			expectFatal:         true,
+			expectPods:          []*apiv1.Pod{},
+			expectBlockingPod:   &BlockingPod{Pod: emptyDirSafeToEvictLocalVolumeMultiValSomeMatchingVals, Reason: LocalStorageRequested},
+			expectDaemonSetPods: []*apiv1.Pod{},
+		},
+		{
+			description:         "pod with EmptyDir and SafeToEvictLocalVolumesKey annotation empty values",
+			pods:                []*apiv1.Pod{emptyDirSafeToEvictLocalVolumeMultiValEmpty},
+			pdbs:                []*policyv1.PodDisruptionBudget{},
+			rcs:                 []*apiv1.ReplicationController{&rc},
+			expectFatal:         true,
+			expectPods:          []*apiv1.Pod{},
+			expectBlockingPod:   &BlockingPod{Pod: emptyDirSafeToEvictLocalVolumeMultiValEmpty, Reason: LocalStorageRequested},
+			expectDaemonSetPods: []*apiv1.Pod{},
+		},
 		{
 			description:         "failed pod",
 			pods:                []*apiv1.Pod{failedPod},