Ubernetes Lite: Volumes can dictate zone scheduling

For AWS EBS, a volume can only be attached to a node in the same AZ.
The scheduler must therefore detect if a volume is being attached to a
pod, and ensure that the pod is scheduled on a node in the same AZ as
the volume.

So that the scheduler need not query the cloud provider every time, and
to support decoupled operation (e.g. bare metal) we tag the volume with
our placement labels.  This is done automatically by means of an
admission controller on AWS when a PersistentVolume is created backed by
an EBS volume.

Support for tagging GCE PVs will follow.

Pods that specify a volume directly (i.e. without using a
PersistentVolumeClaim) will not currently be scheduled correctly (i.e.
they will be scheduled without zone-awareness).

pkg/client/cache/listers.go

@@ -417,3 +417,42 @@ func (s *StoreToJobLister) GetPodJobs(pod *api.Pod) (jobs []extensions.Job, err
 	}
 	return
 }
+
+// Typed wrapper around a store of PersistentVolumes
+type StoreToPVFetcher struct {
+	Store
+}
+
+// GetPersistentVolumeInfo returns cached data for the PersistentVolume 'id'.
+func (s *StoreToPVFetcher) GetPersistentVolumeInfo(id string) (*api.PersistentVolume, error) {
+	o, exists, err := s.Get(&api.PersistentVolume{ObjectMeta: api.ObjectMeta{Name: id}})
+
+	if err != nil {
+		return nil, fmt.Errorf("error retrieving PersistentVolume '%v' from cache: %v", id, err)
+	}
+
+	if !exists {
+		return nil, fmt.Errorf("PersistentVolume '%v' is not in cache", id)
+	}
+
+	return o.(*api.PersistentVolume), nil
+}
+
+// Typed wrapper around a store of PersistentVolumeClaims
+type StoreToPVCFetcher struct {
+	Store
+}
+
+// GetPersistentVolumeClaimInfo returns cached data for the PersistentVolumeClaim 'id'.
+func (s *StoreToPVCFetcher) GetPersistentVolumeClaimInfo(namespace string, id string) (*api.PersistentVolumeClaim, error) {
+	o, exists, err := s.Get(&api.PersistentVolumeClaim{ObjectMeta: api.ObjectMeta{Namespace: namespace, Name: id}})
+	if err != nil {
+		return nil, fmt.Errorf("error retrieving PersistentVolumeClaim '%s/%s' from cache: %v", namespace, id, err)
+	}
+
+	if !exists {
+		return nil, fmt.Errorf("PersistentVolumeClaim '%s/%s' is not in cache", namespace, id)
+	}
+
+	return o.(*api.PersistentVolumeClaim), nil
+}