Add a system modeler to scheduler

So it can try to predict the effect its bindings will have.

plugin/pkg/scheduler/factory/factory.go

@@ -41,23 +41,31 @@ type ConfigFactory struct {
 	Client *client.Client
 	// queue for pods that need scheduling
 	PodQueue *cache.FIFO
-	// a means to list all scheduled pods
-	PodLister *cache.StoreToPodLister
+	// a means to list all known scheduled pods.
+	ScheduledPodLister *cache.StoreToPodLister
+	// a means to list all known scheduled pods and pods assumed to have been scheduled.
+	PodLister algorithm.PodLister
 	// a means to list all minions
 	NodeLister *cache.StoreToNodeLister
 	// a means to list all services
 	ServiceLister *cache.StoreToServiceLister
+
+	modeler scheduler.SystemModeler
 }
 
 // Initializes the factory.
 func NewConfigFactory(client *client.Client) *ConfigFactory {
-	return &ConfigFactory{
-		Client:        client,
-		PodQueue:      cache.NewFIFO(cache.MetaNamespaceKeyFunc),
-		PodLister:     &cache.StoreToPodLister{cache.NewStore(cache.MetaNamespaceKeyFunc)},
-		NodeLister:    &cache.StoreToNodeLister{cache.NewStore(cache.MetaNamespaceKeyFunc)},
-		ServiceLister: &cache.StoreToServiceLister{cache.NewStore(cache.MetaNamespaceKeyFunc)},
+	c := &ConfigFactory{
+		Client:             client,
+		PodQueue:           cache.NewFIFO(cache.MetaNamespaceKeyFunc),
+		ScheduledPodLister: &cache.StoreToPodLister{cache.NewStore(cache.MetaNamespaceKeyFunc)},
+		NodeLister:         &cache.StoreToNodeLister{cache.NewStore(cache.MetaNamespaceKeyFunc)},
+		ServiceLister:      &cache.StoreToServiceLister{cache.NewStore(cache.MetaNamespaceKeyFunc)},
 	}
+	modeler := scheduler.NewSimpleModeler(&cache.StoreToPodLister{c.PodQueue}, c.ScheduledPodLister)
+	c.modeler = modeler
+	c.PodLister = modeler.PodLister()
+	return c
 }
 
 // Create creates a scheduler with the default algorithm provider.
@@ -118,7 +126,7 @@ func (f *ConfigFactory) CreateFromKeys(predicateKeys, priorityKeys util.StringSe
 
 	// Watch and cache all running pods. Scheduler needs to find all pods
 	// so it knows where it's safe to place a pod. Cache this locally.
-	cache.NewReflector(f.createAssignedPodLW(), &api.Pod{}, f.PodLister.Store, 0).Run()
+	cache.NewReflector(f.createAssignedPodLW(), &api.Pod{}, f.ScheduledPodLister.Store, 0).Run()
 
 	// Watch minions.
 	// Minions may be listed frequently, so provide a local up-to-date cache.
@@ -148,6 +156,7 @@ func (f *ConfigFactory) CreateFromKeys(predicateKeys, priorityKeys util.StringSe
 	}
 
 	return &scheduler.Config{
+		Modeler:      f.modeler,
 		MinionLister: f.NodeLister,
 		Algorithm:    algo,
 		Binder:       &binder{f.Client},

plugin/pkg/scheduler/modeler.go

@@ -0,0 +1,155 @@
+/*
+Copyright 2015 Google Inc. 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 scheduler
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/client/cache"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/labels"
+	algorithm "github.com/GoogleCloudPlatform/kubernetes/pkg/scheduler"
+
+	"github.com/golang/glog"
+)
+
+var (
+	_ = SystemModeler(&FakeModeler{})
+	_ = SystemModeler(&SimpleModeler{})
+)
+
+// ExtendedPodLister: SimpleModeler needs to be able to check for a pod's
+// existance in addition to listing the pods.
+type ExtendedPodLister interface {
+	algorithm.PodLister
+	Exists(pod *api.Pod) (bool, error)
+}
+
+// FakeModeler implements the SystemModeler interface.
+type FakeModeler struct {
+	AssumePodFunc func(pod *api.Pod)
+}
+
+// AssumePod calls the function variable if it is not nil.
+func (f *FakeModeler) AssumePod(pod *api.Pod) {
+	if f.AssumePodFunc != nil {
+		f.AssumePodFunc(pod)
+	}
+}
+
+// SimpleModeler implements the SystemModeler interface with a timed pod cache.
+type SimpleModeler struct {
+	queuedPods    ExtendedPodLister
+	scheduledPods ExtendedPodLister
+
+	// assumedPods holds the pods that we think we've scheduled, but that
+	// haven't yet shown up in the scheduledPods variable.
+	// TODO: periodically clear this.
+	assumedPods *cache.StoreToPodLister
+}
+
+// NewSimpleModeler returns a new SimpleModeler.
+//   queuedPods: a PodLister that will return pods that have not been scheduled yet.
+//   scheduledPods: a PodLister that will return pods that we know for sure have been scheduled.
+func NewSimpleModeler(queuedPods, scheduledPods ExtendedPodLister) *SimpleModeler {
+	return &SimpleModeler{
+		queuedPods:    queuedPods,
+		scheduledPods: scheduledPods,
+		assumedPods:   &cache.StoreToPodLister{cache.NewStore(cache.MetaNamespaceKeyFunc)},
+	}
+}
+
+func (s *SimpleModeler) AssumePod(pod *api.Pod) {
+	s.assumedPods.Add(pod)
+}
+
+// Extract names for readable logging.
+func podNames(pods []api.Pod) []string {
+	out := make([]string, len(pods))
+	for i := range pods {
+		out[i] = fmt.Sprintf("'%v/%v (%v)'", pods[i].Namespace, pods[i].Name, pods[i].UID)
+	}
+	return out
+}
+
+func (s *SimpleModeler) listPods(selector labels.Selector) (pods []api.Pod, err error) {
+	assumed, err := s.assumedPods.List(selector)
+	if err != nil {
+		return nil, err
+	}
+	// Since the assumed list will be short, just check every one.
+	// Goal here is to stop making assumptions about a pod once it shows
+	// up in one of these other lists.
+	// TODO: there's a possibility that a pod could get deleted at the
+	//       exact wrong time and linger in assumedPods forever. So we
+	//       need go through that periodically and check for deleted
+	//       pods.
+	for _, pod := range assumed {
+		qExist, err := s.queuedPods.Exists(&pod)
+		if err != nil {
+			return nil, err
+		}
+		if qExist {
+			s.assumedPods.Store.Delete(&pod)
+			continue
+		}
+		sExist, err := s.scheduledPods.Exists(&pod)
+		if err != nil {
+			return nil, err
+		}
+		if sExist {
+			s.assumedPods.Store.Delete(&pod)
+			continue
+		}
+	}
+
+	scheduled, err := s.scheduledPods.List(selector)
+	if err != nil {
+		return nil, err
+	}
+	// re-get in case we deleted any.
+	assumed, err = s.assumedPods.List(selector)
+	if err != nil {
+		return nil, err
+	}
+	if len(assumed) == 0 {
+		return scheduled, nil
+	}
+	glog.V(2).Infof(
+		"listing pods: [%v] assumed to exist in addition to %v known pods.",
+		strings.Join(podNames(assumed), ","),
+		len(scheduled),
+	)
+	return append(scheduled, assumed...), nil
+}
+
+// PodLister returns a PodLister that will list pods that we think we have scheduled in
+// addition to pods that we know have been scheduled.
+func (s *SimpleModeler) PodLister() algorithm.PodLister {
+	return simpleModelerPods{s}
+}
+
+// simpleModelerPods is an adaptor so that SimpleModeler can be a PodLister.
+type simpleModelerPods struct {
+	simpleModeler *SimpleModeler
+}
+
+// List returns pods known and assumed to exist.
+func (s simpleModelerPods) List(selector labels.Selector) (pods []api.Pod, err error) {
+	return s.simpleModeler.listPods(selector)
+}

plugin/pkg/scheduler/modeler_test.go

@@ -0,0 +1,111 @@
+/*
+Copyright 2015 Google Inc. 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 scheduler
+
+import (
+	"testing"
+
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/client/cache"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/labels"
+)
+
+type nn struct {
+	namespace, name string
+}
+
+type names []nn
+
+func (ids names) list() []api.Pod {
+	out := make([]api.Pod, len(ids))
+	for i, id := range ids {
+		out[i] = api.Pod{
+			ObjectMeta: api.ObjectMeta{
+				Namespace: id.namespace,
+				Name:      id.name,
+			},
+		}
+	}
+	return out
+}
+
+func (ids names) has(pod *api.Pod) bool {
+	for _, id := range ids {
+		if pod.Namespace == id.namespace && pod.Name == id.name {
+			return true
+		}
+	}
+	return false
+}
+
+func TestModeler(t *testing.T) {
+	table := []struct {
+		queuedPods    []api.Pod
+		scheduledPods []api.Pod
+		assumedPods   []api.Pod
+		expectPods    names
+	}{
+		{
+			queuedPods:    names{}.list(),
+			scheduledPods: names{{"default", "foo"}, {"custom", "foo"}}.list(),
+			assumedPods:   names{{"default", "foo"}}.list(),
+			expectPods:    names{{"default", "foo"}, {"custom", "foo"}},
+		}, {
+			queuedPods:    names{}.list(),
+			scheduledPods: names{{"default", "foo"}}.list(),
+			assumedPods:   names{{"default", "foo"}, {"custom", "foo"}}.list(),
+			expectPods:    names{{"default", "foo"}, {"custom", "foo"}},
+		}, {
+			queuedPods:    names{{"custom", "foo"}}.list(),
+			scheduledPods: names{{"default", "foo"}}.list(),
+			assumedPods:   names{{"default", "foo"}, {"custom", "foo"}}.list(),
+			expectPods:    names{{"default", "foo"}},
+		},
+	}
+
+	for _, item := range table {
+		q := &cache.StoreToPodLister{cache.NewStore(cache.MetaNamespaceKeyFunc)}
+		for i := range item.queuedPods {
+			q.Store.Add(&item.queuedPods[i])
+		}
+		s := &cache.StoreToPodLister{cache.NewStore(cache.MetaNamespaceKeyFunc)}
+		for i := range item.scheduledPods {
+			s.Store.Add(&item.scheduledPods[i])
+		}
+		m := NewSimpleModeler(q, s)
+		for i := range item.assumedPods {
+			m.AssumePod(&item.assumedPods[i])
+		}
+
+		list, err := m.PodLister().List(labels.Everything())
+		if err != nil {
+			t.Errorf("unexpected error: %v", err)
+		}
+
+		found := 0
+		for _, pod := range list {
+			if item.expectPods.has(&pod) {
+				found++
+			} else {
+				t.Errorf("found unexpected pod %#v", pod)
+			}
+		}
+		if e, a := item.expectPods, found; len(e) != a {
+			t.Errorf("Expected pods:\n%+v\nFound pods:\n%v\n", e, list)
+		}
+	}
+}

plugin/pkg/scheduler/scheduler.go

@@ -31,6 +31,21 @@ type Binder interface {
 	Bind(binding *api.Binding) error
 }
 
+// SystemModeler can help scheduler produce a model of the system that
+// anticipates reality. For example, if scheduler has pods A and B both
+// using hostPort 80, when it binds A to machine M it should not bind B
+// to machine M in the time when it hasn't observed the binding of A
+// take effect yet.
+//
+// Since the model is only an optimization, it's expected to handle
+// any errors itself without sending them back to the scheduler.
+type SystemModeler interface {
+	// AssumePod assumes that the given pod exists in the system.
+	// The assumtion should last until the system confirms the
+	// assumtion or disconfirms it.
+	AssumePod(pod *api.Pod)
+}
+
 // Scheduler watches for new unscheduled pods. It attempts to find
 // minions that they fit on and writes bindings back to the api server.
 type Scheduler struct {
@@ -38,6 +53,9 @@ type Scheduler struct {
 }
 
 type Config struct {
+	// It is expected that changes made via modeler will be observed
+	// by MinionLister and Algorithm.
+	Modeler      SystemModeler
 	MinionLister scheduler.MinionLister
 	Algorithm    scheduler.Scheduler
 	Binder       Binder
@@ -93,4 +111,9 @@ func (s *Scheduler) scheduleOne() {
 		return
 	}
 	s.config.Recorder.Eventf(pod, "scheduled", "Successfully assigned %v to %v", pod.Name, dest)
+	// tell the model to assume that this binding took effect.
+	assumed := *pod
+	assumed.Spec.Host = dest
+	assumed.Status.Host = dest
+	s.config.Modeler.AssumePod(&assumed)
 }

plugin/pkg/scheduler/scheduler_test.go

@@ -34,8 +34,16 @@ type fakeBinder struct {
 
 func (fb fakeBinder) Bind(binding *api.Binding) error { return fb.b(binding) }
 
-func podWithID(id string) *api.Pod {
-	return &api.Pod{ObjectMeta: api.ObjectMeta{Name: id, SelfLink: testapi.SelfLink("pods", id)}}
+func podWithID(id, desiredHost string) *api.Pod {
+	return &api.Pod{
+		ObjectMeta: api.ObjectMeta{Name: id, SelfLink: testapi.SelfLink("pods", id)},
+		Spec: api.PodSpec{
+			Host: desiredHost,
+		},
+		Status: api.PodStatus{
+			Host: desiredHost,
+		},
+	}
 }
 
 type mockScheduler struct {
@@ -53,32 +61,34 @@ func TestScheduler(t *testing.T) {
 	errB := errors.New("binder")
 
 	table := []struct {
-		injectBindError error
-		sendPod         *api.Pod
-		algo            scheduler.Scheduler
-		expectErrorPod  *api.Pod
-		expectError     error
-		expectBind      *api.Binding
-		eventReason     string
+		injectBindError  error
+		sendPod          *api.Pod
+		algo             scheduler.Scheduler
+		expectErrorPod   *api.Pod
+		expectAssumedPod *api.Pod
+		expectError      error
+		expectBind       *api.Binding
+		eventReason      string
 	}{
 		{
-			sendPod:     podWithID("foo"),
-			algo:        mockScheduler{"machine1", nil},
-			expectBind:  &api.Binding{ObjectMeta: api.ObjectMeta{Name: "foo"}, Target: api.ObjectReference{Kind: "Node", Name: "machine1"}},
-			eventReason: "scheduled",
+			sendPod:          podWithID("foo", ""),
+			algo:             mockScheduler{"machine1", nil},
+			expectBind:       &api.Binding{ObjectMeta: api.ObjectMeta{Name: "foo"}, Target: api.ObjectReference{Kind: "Node", Name: "machine1"}},
+			expectAssumedPod: podWithID("foo", "machine1"),
+			eventReason:      "scheduled",
 		}, {
-			sendPod:        podWithID("foo"),
+			sendPod:        podWithID("foo", ""),
 			algo:           mockScheduler{"machine1", errS},
 			expectError:    errS,
-			expectErrorPod: podWithID("foo"),
+			expectErrorPod: podWithID("foo", ""),
 			eventReason:    "failedScheduling",
 		}, {
-			sendPod:         podWithID("foo"),
+			sendPod:         podWithID("foo", ""),
 			algo:            mockScheduler{"machine1", nil},
 			expectBind:      &api.Binding{ObjectMeta: api.ObjectMeta{Name: "foo"}, Target: api.ObjectReference{Kind: "Node", Name: "machine1"}},
 			injectBindError: errB,
 			expectError:     errB,
-			expectErrorPod:  podWithID("foo"),
+			expectErrorPod:  podWithID("foo", ""),
 			eventReason:     "failedScheduling",
 		},
 	}
@@ -86,8 +96,14 @@ func TestScheduler(t *testing.T) {
 	for i, item := range table {
 		var gotError error
 		var gotPod *api.Pod
+		var gotAssumedPod *api.Pod
 		var gotBinding *api.Binding
 		c := &Config{
+			Modeler: &FakeModeler{
+				AssumePodFunc: func(pod *api.Pod) {
+					gotAssumedPod = pod
+				},
+			},
 			MinionLister: scheduler.FakeMinionLister(
 				api.NodeList{Items: []api.Node{{ObjectMeta: api.ObjectMeta{Name: "machine1"}}}},
 			),
@@ -114,6 +130,9 @@ func TestScheduler(t *testing.T) {
 			close(called)
 		})
 		s.scheduleOne()
+		if e, a := item.expectAssumedPod, gotAssumedPod; !reflect.DeepEqual(e, a) {
+			t.Errorf("%v: assumed pod: wanted %v, got %v", i, e, a)
+		}
 		if e, a := item.expectErrorPod, gotPod; !reflect.DeepEqual(e, a) {
 			t.Errorf("%v: error pod: wanted %v, got %v", i, e, a)
 		}