Adds support for PodCIDR allocation from the GCE cloud provider

If CIDRAllocatorType is set to `CloudCIDRAllocator`, then allocation
of CIDR allocation instead is done by the external cloud provider and
the node controller is only responsible for reflecting the allocation
into the node spec.

- Splits off the rangeAllocator from the cidr_allocator.go file.
- Adds cloudCIDRAllocator, which is used when the cloud provider allocates
  the CIDR ranges externally. (GCE support only)
- Updates RBAC permission for node controller to include PATCH

pkg/controller/node/cloud_cidr_allocator.go

@@ -0,0 +1,143 @@
+/*
+Copyright 2016 The Kubernetes Authors.
+
+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 node
+
+import (
+	"fmt"
+	"sync"
+
+	"github.com/golang/glog"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/types"
+
+	clientv1 "k8s.io/client-go/pkg/api/v1"
+	"k8s.io/client-go/tools/record"
+
+	"k8s.io/kubernetes/pkg/api"
+	"k8s.io/kubernetes/pkg/api/v1"
+	"k8s.io/kubernetes/pkg/client/clientset_generated/clientset"
+	"k8s.io/kubernetes/pkg/cloudprovider"
+	"k8s.io/kubernetes/pkg/cloudprovider/providers/gce"
+	nodeutil "k8s.io/kubernetes/pkg/util/node"
+)
+
+// cloudCIDRAllocator allocates node CIDRs according to IP address aliases
+// assigned by the cloud provider. In this case, the allocation and
+// deallocation is delegated to the external provider, and the controller
+// merely takes the assignment and updates the node spec.
+type cloudCIDRAllocator struct {
+	lock sync.Mutex
+
+	client clientset.Interface
+	cloud  *gce.GCECloud
+
+	recorder record.EventRecorder
+}
+
+var _ CIDRAllocator = (*cloudCIDRAllocator)(nil)
+
+func NewCloudCIDRAllocator(
+	client clientset.Interface,
+	cloud cloudprovider.Interface) (ca CIDRAllocator, err error) {
+
+	gceCloud, ok := cloud.(*gce.GCECloud)
+	if !ok {
+		err = fmt.Errorf("cloudCIDRAllocator does not support %v provider", cloud.ProviderName())
+		return
+	}
+
+	ca = &cloudCIDRAllocator{
+		client: client,
+		cloud:  gceCloud,
+		recorder: record.NewBroadcaster().NewRecorder(
+			api.Scheme,
+			clientv1.EventSource{Component: "cidrAllocator"}),
+	}
+
+	glog.V(0).Infof("Using cloud CIDR allocator (provider: %v)", cloud.ProviderName())
+
+	return
+}
+
+func (ca *cloudCIDRAllocator) AllocateOrOccupyCIDR(node *v1.Node) error {
+	glog.V(2).Infof("Updating PodCIDR for node %v", node.Name)
+
+	cidrs, err := ca.cloud.AliasRanges(types.NodeName(node.Name))
+
+	if err != nil {
+		recordNodeStatusChange(ca.recorder, node, "CIDRNotAvailable")
+		return fmt.Errorf("failed to allocate cidr: %v", err)
+	}
+
+	if len(cidrs) == 0 {
+		recordNodeStatusChange(ca.recorder, node, "CIDRNotAvailable")
+		glog.V(2).Infof("Node %v has no CIDRs", node.Name)
+		return fmt.Errorf("failed to allocate cidr (none exist)")
+	}
+
+	node, err = ca.client.Core().Nodes().Get(node.Name, metav1.GetOptions{})
+	if err != nil {
+		glog.Errorf("Could not get Node object from Kubernetes: %v", err)
+		return err
+	}
+
+	podCIDR := cidrs[0]
+
+	if node.Spec.PodCIDR != "" {
+		if node.Spec.PodCIDR == podCIDR {
+			glog.V(3).Infof("Node %v has PodCIDR %v", node.Name, podCIDR)
+			return nil
+		}
+		glog.Errorf("PodCIDR cannot be reassigned, node %v spec has %v, but cloud provider has assigned %v",
+			node.Name, node.Spec.PodCIDR, podCIDR)
+		// We fall through and set the CIDR despite this error. This
+		// implements the same logic as implemented in the
+		// rangeAllocator.
+		//
+		// See https://github.com/kubernetes/kubernetes/pull/42147#discussion_r103357248
+	}
+
+	node.Spec.PodCIDR = cidrs[0]
+	if _, err := ca.client.Core().Nodes().Update(node); err == nil {
+		glog.V(2).Infof("Node %v PodCIDR set to %v", node.Name, podCIDR)
+	} else {
+		glog.Errorf("Could not update node %v PodCIDR to %v: %v",
+			node.Name, podCIDR, err)
+		return err
+	}
+
+	err = nodeutil.SetNodeCondition(ca.client, types.NodeName(node.Name), v1.NodeCondition{
+		Type:               v1.NodeNetworkUnavailable,
+		Status:             v1.ConditionFalse,
+		Reason:             "RouteCreated",
+		Message:            "NodeController create implicit route",
+		LastTransitionTime: metav1.Now(),
+	})
+	if err != nil {
+		glog.Errorf("Error setting route status for node %v: %v",
+			node.Name, err)
+	}
+
+	return err
+}
+
+func (ca *cloudCIDRAllocator) ReleaseCIDR(node *v1.Node) error {
+	glog.V(2).Infof("Node %v PodCIDR (%v) will be released by external cloud provider (not managed by controller)",
+		node.Name, node.Spec.PodCIDR)
+	return nil
+}