Merge pull request #40952 from dashpole/premption

Automatic merge from submit-queue (batch tested with PRs 41994, 41969, 41997, 40952, 40576)

Guaranteed admission for Critical Pods

This is the first step in implementing node-level preemption for critical pods.
It defines the AdmissionFailureHandler interface, which allows callers, like the kubelet, to define how failed predicates are handled, and take steps to correct failures if necessary.
In the kubelet's implementation, it triggers preemption if the pod being admitted is critical, and if the only failed predicates are InsufficientResourceErrors, then it prempts (not yet implemented) other other pods to allow admission of the critical pod.

cc: @vishh

pkg/api/v1/resource_helpers.go

@@ -227,3 +227,31 @@ func PodRequestsAndLimits(pod *Pod) (reqs map[ResourceName]resource.Quantity, li
 	}
 	return
 }
+
+// finds and returns the request for a specific resource.
+func GetResourceRequest(pod *Pod, resource ResourceName) int64 {
+	if resource == ResourcePods {
+		return 1
+	}
+	totalResources := int64(0)
+	for _, container := range pod.Spec.Containers {
+		if rQuantity, ok := container.Resources.Requests[resource]; ok {
+			if resource == ResourceCPU {
+				totalResources += rQuantity.MilliValue()
+			} else {
+				totalResources += rQuantity.Value()
+			}
+		}
+	}
+	// take max_resource(sum_pod, any_init_container)
+	for _, container := range pod.Spec.InitContainers {
+		if rQuantity, ok := container.Resources.Requests[resource]; ok {
+			if resource == ResourceCPU && rQuantity.MilliValue() > totalResources {
+				totalResources = rQuantity.MilliValue()
+			} else if rQuantity.Value() > totalResources {
+				totalResources = rQuantity.Value()
+			}
+		}
+	}
+	return totalResources
+}