Merge pull request kubernetes#23254 from jsafrane/devel/ulimited-aws-…

…devices

Automatic merge from submit-queue

AWS: Move enforcement of attached AWS device limit from kubelet to scheduler

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').

Note that the scheduler counts only *pods* assigned to a node. When a pod is deleted and a new pod is scheduled on a node, kubelet start (slowly) detaching the old volume and (slowly) attaching the new volume. Depending on AWS speed **it may happen that more than KUBE_MAX_PD_VOLS volumes are actually attached to a node for some time!** Kubelet will clean it up in few seconds / minutes (both attach/detach is quite slow).

Fixes kubernetes#22994

pkg/cloudprovider/providers/aws/aws.go

@@ -910,23 +910,6 @@ 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
 
@@ -1056,19 +1039,20 @@ 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)
 	}