Set GCE PD attachable volume limit based on machineType

This PR implements the function to return attachable volume limit based
on machineType for GCE PD. This is part of the design in kubernetes/community#2051/

pkg/volume/gce_pd/gce_pd.go

@@ -17,10 +17,12 @@ limitations under the License.
 package gce_pd
 
 import (
+	"context"
 	"fmt"
 	"os"
 	"path"
 	"strconv"
+	"strings"
 
 	"github.com/golang/glog"
 	"k8s.io/api/core/v1"
@@ -56,6 +58,18 @@ const (
 	gcePersistentDiskPluginName = "kubernetes.io/gce-pd"
 )
 
+// The constants are used to map from the machine type (number of CPUs) to the limit of
+// persistent disks that can be attached to an instance. Please refer to gcloud doc
+// https://cloud.google.com/compute/docs/disks/#increased_persistent_disk_limits
+const (
+	OneCPU         = 1
+	EightCPUs      = 8
+	VolumeLimit16  = 16
+	VolumeLimit32  = 32
+	VolumeLimit64  = 64
+	VolumeLimit128 = 128
+)
+
 func getPath(uid types.UID, volName string, host volume.VolumeHost) string {
 	return host.GetPodVolumeDir(uid, kstrings.EscapeQualifiedNameForDisk(gcePersistentDiskPluginName), volName)
 }
@@ -104,7 +118,7 @@ func (plugin *gcePersistentDiskPlugin) GetAccessModes() []v1.PersistentVolumeAcc
 
 func (plugin *gcePersistentDiskPlugin) GetVolumeLimits() (map[string]int64, error) {
 	volumeLimits := map[string]int64{
-		util.GCEVolumeLimitKey: 16,
+		util.GCEVolumeLimitKey: VolumeLimit16,
 	}
 	cloud := plugin.host.GetCloudProvider()
 
@@ -120,6 +134,33 @@ func (plugin *gcePersistentDiskPlugin) GetVolumeLimits() (map[string]int64, erro
 		return nil, fmt.Errorf("Expected gce cloud got %s", cloud.ProviderName())
 	}
 
+	instances, ok := cloud.Instances()
+	if !ok {
+		glog.Warning("Failed to get instances from cloud provider")
+		return volumeLimits, nil
+	}
+
+	instanceType, err := instances.InstanceType(context.TODO(), plugin.host.GetNodeName())
+	if err != nil {
+		glog.Errorf("Failed to get instance type from GCE cloud provider")
+		return volumeLimits, nil
+	}
+	if strings.HasPrefix(instanceType, "n1-") {
+		splits := strings.Split(instanceType, "-")
+		if len(splits) < 3 {
+			return volumeLimits, nil
+		}
+		last := splits[2]
+		if num, err := strconv.Atoi(last); err == nil {
+			if num == OneCPU {
+				volumeLimits[util.GCEVolumeLimitKey] = VolumeLimit32
+			} else if num < EightCPUs {
+				volumeLimits[util.GCEVolumeLimitKey] = VolumeLimit64
+			} else {
+				volumeLimits[util.GCEVolumeLimitKey] = VolumeLimit128
+			}
+		}
+	}
 	return volumeLimits, nil
 }