Remove limit of attached AWS devices from kubelet.

Limit of nr. of attached EBS volumes to a node is now enforced by scheduler. It
can be adjusted by KUBE_MAX_PD_VOLS env. variable there.

Therefore we don't need the same check in kubelet. If the system admin wants to
attach more, we should allow it.

Kubelet limit is now 650 attached volumes ('ba'..'zz').

pkg/cloudprovider/providers/aws/aws.go

@@ -904,23 +904,6 @@ type awsInstanceType struct {
 // This should be stored as a single letter (i.e. c, not sdc or /dev/sdc)
 type mountDevice string
 
-// TODO: Also return number of mounts allowed?
-func (self *awsInstanceType) getEBSMountDevices() []mountDevice {
-	// See: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/block-device-mapping-concepts.html
-	// We will generate "ba", "bb", "bc"..."bz", "ca", ..., up to DefaultMaxEBSVolumes
-	devices := []mountDevice{}
-	count := 0
-	for first := 'b'; count < DefaultMaxEBSVolumes; first++ {
-		for second := 'a'; count < DefaultMaxEBSVolumes && second <= 'z'; second++ {
-			device := mountDevice(fmt.Sprintf("%c%c", first, second))
-			devices = append(devices, device)
-			count++
-		}
-	}
-
-	return devices
-}
-
 type awsInstance struct {
 	ec2 EC2
 
@@ -1050,19 +1033,20 @@ func (self *awsInstance) getMountDevice(volumeID string, assign bool) (assigned
 		return mountDevice(""), false, nil
 	}
 
-	// Check all the valid mountpoints to see if any of them are free
-	valid := instanceType.getEBSMountDevices()
-	chosen := mountDevice("")
-	for _, mountDevice := range valid {
-		_, found := deviceMappings[mountDevice]
-		if !found {
-			chosen = mountDevice
-			break
+	// Find the first unused device in sequence 'ba', 'bb', 'bc', ... 'bz', 'ca', ... 'zz'
+	var chosen mountDevice
+	for first := 'b'; first <= 'z' && chosen == ""; first++ {
+		for second := 'a'; second <= 'z' && chosen == ""; second++ {
+			candidate := mountDevice(fmt.Sprintf("%c%c", first, second))
+			if _, found := deviceMappings[candidate]; !found {
+				chosen = candidate
+				break
+			}
 		}
 	}
 
 	if chosen == "" {
-		glog.Warningf("Could not assign a mount device (all in use?).  mappings=%v, valid=%v", deviceMappings, valid)
+		glog.Warningf("Could not assign a mount device (all in use?).  mappings=%v", deviceMappings)
 		return "", false, fmt.Errorf("Too many EBS volumes attached to node %s.", self.nodeName)
 	}