Scheduler predicate for capping node volume count

For certain volume types (e.g. AWS EBS or GCE PD), a limitted
number of such volumes can be attached to a given node.  This commit
introduces a predicate with allows cluster admins to cap
the maximum number of volumes matching a particular type attached to a
given node.

The volume type is configurable by passing a pair of filter functions,
and the maximum number of such volumes is configurable to allow node
admins to reserve a certain number of volumes for system use.

By default, the predicate is exposed as MaxEBSVolumeCount and
MaxGCEPDVolumeCount (for AWS ElasticBlocKStore and GCE PersistentDisk
volumes, respectively), each of which can be configured using the
`KUBE_MAX_PD_VOLS` environment variable.

Fixes #7835

docs/devel/scheduler_algorithm.md

@@ -47,6 +47,8 @@ The purpose of filtering the nodes is to filter out the nodes that do not meet c
 - `PodFitsHost`: Filter out all nodes except the one specified in the PodSpec's NodeName field.
 - `PodSelectorMatches`: Check if the labels of the node match the labels specified in the Pod's `nodeSelector` field ([Here](../user-guide/node-selection/) is an example of how to use `nodeSelector` field).
 - `CheckNodeLabelPresence`: Check if all the specified labels exist on a node or not, regardless of the value.
+- `MaxEBSVolumeCount`: Ensure that the number of attached ElasticBlockStore volumes does not exceed a maximum value (by default, 39, since Amazon recommends a maximum of 40 with one of those 40 reserved for the root volume -- see [Amazon's documentation](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/volume_limits.html#linux-specific-volume-limits)).  The maximum value can be controlled by setting the `KUBE_MAX_PD_VOLS` environment variable.
+- `MaxGCEPDVolumeCount`: Ensure that the number of attached GCE PersistentDisk volumes does not exceed a maximum value (by default, 16, which is the maximum GCE allows -- see [GCE's documentation](https://cloud.google.com/compute/docs/disks/persistent-disks#limits_for_predefined_machine_types)).  The maximum value can be controlled by setting the `KUBE_MAX_PD_VOLS` environment variable.
 
 The details of the above predicates can be found in [plugin/pkg/scheduler/algorithm/predicates/predicates.go](http://releases.k8s.io/HEAD/plugin/pkg/scheduler/algorithm/predicates/predicates.go). All predicates mentioned above can be used in combination to perform a sophisticated filtering policy. Kubernetes uses some, but not all, of these predicates by default. You can see which ones are used by default in [plugin/pkg/scheduler/algorithmprovider/defaults/defaults.go](http://releases.k8s.io/HEAD/plugin/pkg/scheduler/algorithmprovider/defaults/defaults.go).
 

plugin/pkg/scheduler/algorithm/predicates/predicates.go

@@ -145,6 +145,141 @@ func NoDiskConflict(pod *api.Pod, existingPods []*api.Pod, node string) (bool, e
 	return true, nil
 }
 
+type MaxPDVolumeCountChecker struct {
+	filter     VolumeFilter
+	maxVolumes int
+	pvInfo     PersistentVolumeInfo
+	pvcInfo    PersistentVolumeClaimInfo
+}
+
+// VolumeFilter contains information on how to filter PD Volumes when checking PD Volume caps
+type VolumeFilter struct {
+	// Filter normal volumes
+	FilterVolume           func(vol *api.Volume) (id string, relevant bool)
+	FilterPersistentVolume func(pv *api.PersistentVolume) (id string, relevant bool)
+}
+
+// NewMaxPDVolumeCountPredicate creates a predicate which evaluates whether a pod can fit based on the
+// number of volumes which match a filter that it requests, and those that are already present.  The
+// maximum number is configurable to accommodate different systems.
+//
+// The predicate looks for both volumes used directly, as well as PVC volumes that are backed by relevant volume
+// types, counts the number of unique volumes, and rejects the new pod if it would place the total count over
+// the maximum.
+func NewMaxPDVolumeCountPredicate(filter VolumeFilter, maxVolumes int, pvInfo PersistentVolumeInfo, pvcInfo PersistentVolumeClaimInfo) algorithm.FitPredicate {
+	c := &MaxPDVolumeCountChecker{
+		filter:     filter,
+		maxVolumes: maxVolumes,
+		pvInfo:     pvInfo,
+		pvcInfo:    pvcInfo,
+	}
+
+	return c.predicate
+}
+
+func (c *MaxPDVolumeCountChecker) filterVolumes(volumes []api.Volume, namespace string, filteredVolumes map[string]bool) error {
+	for _, vol := range volumes {
+		if id, ok := c.filter.FilterVolume(&vol); ok {
+			filteredVolumes[id] = true
+		} else if vol.PersistentVolumeClaim != nil {
+			pvcName := vol.PersistentVolumeClaim.ClaimName
+			if pvcName == "" {
+				return fmt.Errorf("PersistentVolumeClaim had no name: %q", pvcName)
+			}
+			pvc, err := c.pvcInfo.GetPersistentVolumeClaimInfo(namespace, pvcName)
+			if err != nil {
+				return err
+			}
+
+			pvName := pvc.Spec.VolumeName
+			if pvName == "" {
+				return fmt.Errorf("PersistentVolumeClaim is not bound: %q", pvcName)
+			}
+
+			pv, err := c.pvInfo.GetPersistentVolumeInfo(pvName)
+			if err != nil {
+				return err
+			}
+
+			if id, ok := c.filter.FilterPersistentVolume(pv); ok {
+				filteredVolumes[id] = true
+			}
+		}
+	}
+
+	return nil
+}
+
+func (c *MaxPDVolumeCountChecker) predicate(pod *api.Pod, existingPods []*api.Pod, node string) (bool, error) {
+	newVolumes := make(map[string]bool)
+	if err := c.filterVolumes(pod.Spec.Volumes, pod.Namespace, newVolumes); err != nil {
+		return false, err
+	}
+
+	// quick return
+	if len(newVolumes) == 0 {
+		return true, nil
+	}
+
+	// count unique volumes
+	existingVolumes := make(map[string]bool)
+	for _, existingPod := range existingPods {
+		if err := c.filterVolumes(existingPod.Spec.Volumes, existingPod.Namespace, existingVolumes); err != nil {
+			return false, err
+		}
+	}
+	numExistingVolumes := len(existingVolumes)
+
+	// filter out already-mounted volumes
+	for k := range existingVolumes {
+		if _, ok := newVolumes[k]; ok {
+			delete(newVolumes, k)
+		}
+	}
+
+	numNewVolumes := len(newVolumes)
+
+	if numExistingVolumes+numNewVolumes > c.maxVolumes {
+		return false, nil
+	}
+
+	return true, nil
+}
+
+// EBSVolumeFilter is a VolumeFilter for filtering AWS ElasticBlockStore Volumes
+var EBSVolumeFilter VolumeFilter = VolumeFilter{
+	FilterVolume: func(vol *api.Volume) (string, bool) {
+		if vol.AWSElasticBlockStore != nil {
+			return vol.AWSElasticBlockStore.VolumeID, true
+		}
+		return "", false
+	},
+
+	FilterPersistentVolume: func(pv *api.PersistentVolume) (string, bool) {
+		if pv.Spec.AWSElasticBlockStore != nil {
+			return pv.Spec.AWSElasticBlockStore.VolumeID, true
+		}
+		return "", false
+	},
+}
+
+// GCEPDVolumeFilter is a VolumeFilter for filtering GCE PersistentDisk Volumes
+var GCEPDVolumeFilter VolumeFilter = VolumeFilter{
+	FilterVolume: func(vol *api.Volume) (string, bool) {
+		if vol.GCEPersistentDisk != nil {
+			return vol.GCEPersistentDisk.PDName, true
+		}
+		return "", false
+	},
+
+	FilterPersistentVolume: func(pv *api.PersistentVolume) (string, bool) {
+		if pv.Spec.GCEPersistentDisk != nil {
+			return pv.Spec.GCEPersistentDisk.PDName, true
+		}
+		return "", false
+	},
+}
+
 type VolumeZoneChecker struct {
 	nodeInfo NodeInfo
 	pvInfo   PersistentVolumeInfo

plugin/pkg/scheduler/algorithm/predicates/predicates_test.go

@@ -44,6 +44,28 @@ func (nodes FakeNodeListInfo) GetNodeInfo(nodeName string) (*api.Node, error) {
 	return nil, fmt.Errorf("Unable to find node: %s", nodeName)
 }
 
+type FakePersistentVolumeClaimInfo []api.PersistentVolumeClaim
+
+func (pvcs FakePersistentVolumeClaimInfo) GetPersistentVolumeClaimInfo(namespace string, pvcID string) (*api.PersistentVolumeClaim, error) {
+	for _, pvc := range pvcs {
+		if pvc.Name == pvcID && pvc.Namespace == namespace {
+			return &pvc, nil
+		}
+	}
+	return nil, fmt.Errorf("Unable to find persistent volume claim: %s/%s", namespace, pvcID)
+}
+
+type FakePersistentVolumeInfo []api.PersistentVolume
+
+func (pvs FakePersistentVolumeInfo) GetPersistentVolumeInfo(pvID string) (*api.PersistentVolume, error) {
+	for _, pv := range pvs {
+		if pv.Name == pvID {
+			return &pv, nil
+		}
+	}
+	return nil, fmt.Errorf("Unable to find persistent volume: %s", pvID)
+}
+
 func makeResources(milliCPU int64, memory int64, pods int64) api.NodeResources {
 	return api.NodeResources{
 		Capacity: api.ResourceList{
@@ -771,3 +793,224 @@ func TestServiceAffinity(t *testing.T) {
 		}
 	}
 }
+
+func TestEBSVolumeCountConflicts(t *testing.T) {
+	oneVolPod := &api.Pod{
+		Spec: api.PodSpec{
+			Volumes: []api.Volume{
+				{
+					VolumeSource: api.VolumeSource{
+						AWSElasticBlockStore: &api.AWSElasticBlockStoreVolumeSource{VolumeID: "ovp"},
+					},
+				},
+			},
+		},
+	}
+	ebsPVCPod := &api.Pod{
+		Spec: api.PodSpec{
+			Volumes: []api.Volume{
+				{
+					VolumeSource: api.VolumeSource{
+						PersistentVolumeClaim: &api.PersistentVolumeClaimVolumeSource{
+							ClaimName: "someEBSVol",
+						},
+					},
+				},
+			},
+		},
+	}
+	splitPVCPod := &api.Pod{
+		Spec: api.PodSpec{
+			Volumes: []api.Volume{
+				{
+					VolumeSource: api.VolumeSource{
+						PersistentVolumeClaim: &api.PersistentVolumeClaimVolumeSource{
+							ClaimName: "someNonEBSVol",
+						},
+					},
+				},
+				{
+					VolumeSource: api.VolumeSource{
+						PersistentVolumeClaim: &api.PersistentVolumeClaimVolumeSource{
+							ClaimName: "someEBSVol",
+						},
+					},
+				},
+			},
+		},
+	}
+	twoVolPod := &api.Pod{
+		Spec: api.PodSpec{
+			Volumes: []api.Volume{
+				{
+					VolumeSource: api.VolumeSource{
+						AWSElasticBlockStore: &api.AWSElasticBlockStoreVolumeSource{VolumeID: "tvp1"},
+					},
+				},
+				{
+					VolumeSource: api.VolumeSource{
+						AWSElasticBlockStore: &api.AWSElasticBlockStoreVolumeSource{VolumeID: "tvp2"},
+					},
+				},
+			},
+		},
+	}
+	splitVolsPod := &api.Pod{
+		Spec: api.PodSpec{
+			Volumes: []api.Volume{
+				{
+					VolumeSource: api.VolumeSource{
+						HostPath: &api.HostPathVolumeSource{},
+					},
+				},
+				{
+					VolumeSource: api.VolumeSource{
+						AWSElasticBlockStore: &api.AWSElasticBlockStoreVolumeSource{VolumeID: "svp"},
+					},
+				},
+			},
+		},
+	}
+	nonApplicablePod := &api.Pod{
+		Spec: api.PodSpec{
+			Volumes: []api.Volume{
+				{
+					VolumeSource: api.VolumeSource{
+						HostPath: &api.HostPathVolumeSource{},
+					},
+				},
+			},
+		},
+	}
+	emptyPod := &api.Pod{
+		Spec: api.PodSpec{},
+	}
+
+	tests := []struct {
+		newPod       *api.Pod
+		existingPods []*api.Pod
+		maxVols      int
+		fits         bool
+		test         string
+	}{
+		{
+			newPod:       oneVolPod,
+			existingPods: []*api.Pod{twoVolPod, oneVolPod},
+			maxVols:      4,
+			fits:         true,
+			test:         "fits when node capacity >= new pod's EBS volumes",
+		},
+		{
+			newPod:       twoVolPod,
+			existingPods: []*api.Pod{oneVolPod},
+			maxVols:      2,
+			fits:         false,
+			test:         "doesn't fit when node capacity < new pod's EBS volumes",
+		},
+		{
+			newPod:       splitVolsPod,
+			existingPods: []*api.Pod{twoVolPod},
+			maxVols:      3,
+			fits:         true,
+			test:         "new pod's count ignores non-EBS volumes",
+		},
+		{
+			newPod:       twoVolPod,
+			existingPods: []*api.Pod{splitVolsPod, nonApplicablePod, emptyPod},
+			maxVols:      3,
+			fits:         true,
+			test:         "existing pods' counts ignore non-EBS volumes",
+		},
+		{
+			newPod:       ebsPVCPod,
+			existingPods: []*api.Pod{splitVolsPod, nonApplicablePod, emptyPod},
+			maxVols:      3,
+			fits:         true,
+			test:         "new pod's count considers PVCs backed by EBS volumes",
+		},
+		{
+			newPod:       splitPVCPod,
+			existingPods: []*api.Pod{splitVolsPod, oneVolPod},
+			maxVols:      3,
+			fits:         true,
+			test:         "new pod's count ignores PVCs not backed by EBS volumes",
+		},
+		{
+			newPod:       twoVolPod,
+			existingPods: []*api.Pod{oneVolPod, ebsPVCPod},
+			maxVols:      3,
+			fits:         false,
+			test:         "existing pods' counts considers PVCs backed by EBS volumes",
+		},
+		{
+			newPod:       twoVolPod,
+			existingPods: []*api.Pod{oneVolPod, twoVolPod, ebsPVCPod},
+			maxVols:      4,
+			fits:         true,
+			test:         "already-mounted EBS volumes are always ok to allow",
+		},
+		{
+			newPod:       splitVolsPod,
+			existingPods: []*api.Pod{oneVolPod, oneVolPod, ebsPVCPod},
+			maxVols:      3,
+			fits:         true,
+			test:         "the same EBS volumes are not counted multiple times",
+		},
+	}
+
+	pvInfo := FakePersistentVolumeInfo{
+		{
+			ObjectMeta: api.ObjectMeta{Name: "someEBSVol"},
+			Spec: api.PersistentVolumeSpec{
+				PersistentVolumeSource: api.PersistentVolumeSource{
+					AWSElasticBlockStore: &api.AWSElasticBlockStoreVolumeSource{},
+				},
+			},
+		},
+		{
+			ObjectMeta: api.ObjectMeta{Name: "someNonEBSVol"},
+			Spec: api.PersistentVolumeSpec{
+				PersistentVolumeSource: api.PersistentVolumeSource{},
+			},
+		},
+	}
+
+	pvcInfo := FakePersistentVolumeClaimInfo{
+		{
+			ObjectMeta: api.ObjectMeta{Name: "someEBSVol"},
+			Spec:       api.PersistentVolumeClaimSpec{VolumeName: "someEBSVol"},
+		},
+		{
+			ObjectMeta: api.ObjectMeta{Name: "someNonEBSVol"},
+			Spec:       api.PersistentVolumeClaimSpec{VolumeName: "someNonEBSVol"},
+		},
+	}
+
+	filter := VolumeFilter{
+		FilterVolume: func(vol *api.Volume) (string, bool) {
+			if vol.AWSElasticBlockStore != nil {
+				return vol.AWSElasticBlockStore.VolumeID, true
+			}
+			return "", false
+		},
+
+		FilterPersistentVolume: func(pv *api.PersistentVolume) (string, bool) {
+			if pv.Spec.AWSElasticBlockStore != nil {
+				return pv.Spec.AWSElasticBlockStore.VolumeID, true
+			}
+			return "", false
+		},
+	}
+
+	for _, test := range tests {
+		pred := NewMaxPDVolumeCountPredicate(filter, test.maxVols, pvInfo, pvcInfo)
+		fits, err := pred(test.newPod, test.existingPods, "some-node")
+		if err != nil {
+			t.Errorf("unexpected error: %v", err)
+		}
+
+		if fits != test.fits {
+			t.Errorf("%s: expected %v, got %v", test.test, test.fits, fits)
+		}
+	}
+}

plugin/pkg/scheduler/algorithmprovider/defaults/defaults.go

@@ -18,14 +18,41 @@ limitations under the License.
 package defaults
 
 import (
+	"os"
+	"strconv"
+
 	"k8s.io/kubernetes/pkg/util/sets"
 	"k8s.io/kubernetes/plugin/pkg/scheduler"
 	"k8s.io/kubernetes/plugin/pkg/scheduler/algorithm"
 	"k8s.io/kubernetes/plugin/pkg/scheduler/algorithm/predicates"
 	"k8s.io/kubernetes/plugin/pkg/scheduler/algorithm/priorities"
 	"k8s.io/kubernetes/plugin/pkg/scheduler/factory"
+
+	"github.com/golang/glog"
 )
 
+// Amazon reccomends having no more that 40 volumes attached to an instance,
+// and at least one of those is for the system root volume.
+const DefaultMaxEBSVolumes = 39
+
+// GCE instances can have up to 16 PD volumes attached.
+const DefaultMaxGCEPDVolumes = 16
+
+// getMaxVols checks the max PD volumes environment variable, otherwise returning a default value
+func getMaxVols(defaultVal int) int {
+	if rawMaxVols := os.Getenv("KUBE_MAX_PD_VOLS"); rawMaxVols != "" {
+		if parsedMaxVols, err := strconv.Atoi(rawMaxVols); err != nil {
+			glog.Errorf("Unable to parse maxiumum PD volumes value, using default of %v: %v", defaultVal, err)
+		} else if parsedMaxVols <= 0 {
+			glog.Errorf("Maximum PD volumes must be a positive value, using default of %v", defaultVal)
+		} else {
+			return parsedMaxVols
+		}
+	}
+
+	return defaultVal
+}
+
 func init() {
 	factory.RegisterAlgorithmProvider(factory.DefaultProvider, defaultPredicates(), defaultPriorities())
 	// EqualPriority is a prioritizer function that gives an equal weight of one to all nodes
@@ -80,6 +107,26 @@ func defaultPredicates() sets.String {
 		),
 		// Fit is determined by the presence of the Host parameter and a string match
 		factory.RegisterFitPredicate("HostName", predicates.PodFitsHost),
+
+		// Fit is determined by whether or not there would be too many AWS EBS volumes attached to the node
+		factory.RegisterFitPredicateFactory(
+			"MaxEBSVolumeCount",
+			func(args factory.PluginFactoryArgs) algorithm.FitPredicate {
+				// TODO: allow for generically parameterized scheduler predicates, because this is a bit ugly
+				maxVols := getMaxVols(DefaultMaxEBSVolumes)
+				return predicates.NewMaxPDVolumeCountPredicate(predicates.EBSVolumeFilter, maxVols, args.PVInfo, args.PVCInfo)
+			},
+		),
+
+		// Fit is determined by whether or not there would be too many GCE PD volumes attached to the node
+		factory.RegisterFitPredicateFactory(
+			"MaxGCEPDVolumeCount",
+			func(args factory.PluginFactoryArgs) algorithm.FitPredicate {
+				// TODO: allow for generically parameterized scheduler predicates, because this is a bit ugly
+				maxVols := getMaxVols(DefaultMaxGCEPDVolumes)
+				return predicates.NewMaxPDVolumeCountPredicate(predicates.GCEPDVolumeFilter, maxVols, args.PVInfo, args.PVCInfo)
+			},
+		),
 	)
 }