kubelet: don't reject pods without adding them to the pod manager

kubelet relies on the pod manager as a cache of the pods in the apiserver (and
other sources) . The cache should be kept up-to-date even when rejecting pods.
Without this, kubelet may decide at any point to drop the status update
(request to the apiserver) for the rejected pod since it would think the pod no
longer exists in the apiserver.

Also check if the pod to-be-admitted has terminated or not. In the case where
it has terminated, skip the admission process completely.

pkg/kubelet/kubelet.go

@@ -1911,22 +1911,32 @@ func (kl *Kubelet) HandlePodAdditions(pods []*v1.Pod) {
 	start := kl.clock.Now()
 	sort.Sort(sliceutils.PodsByCreationTime(pods))
 	for _, pod := range pods {
+		existingPods := kl.podManager.GetPods()
+		// Always add the pod to the pod manager. Kubelet relies on the pod
+		// manager as the source of truth for the desired state. If a pod does
+		// not exist in the pod manager, it means that it has been deleted in
+		// the apiserver and no action (other than cleanup) is required.
+		kl.podManager.AddPod(pod)
+
 		if kubepod.IsMirrorPod(pod) {
-			kl.podManager.AddPod(pod)
 			kl.handleMirrorPod(pod, start)
 			continue
 		}
-		// Note that allPods excludes the new pod.
-		allPods := kl.podManager.GetPods()
-		// We failed pods that we rejected, so activePods include all admitted
-		// pods that are alive.
-		activePods := kl.filterOutTerminatedPods(allPods)
-		// Check if we can admit the pod; if not, reject it.
-		if ok, reason, message := kl.canAdmitPod(activePods, pod); !ok {
-			kl.rejectPod(pod, reason, message)
-			continue
+
+		if !kl.podIsTerminated(pod) {
+			// Only go through the admission process if the pod is not
+			// terminated.
+
+			// We failed pods that we rejected, so activePods include all admitted
+			// pods that are alive.
+			activePods := kl.filterOutTerminatedPods(existingPods)
+
+			// Check if we can admit the pod; if not, reject it.
+			if ok, reason, message := kl.canAdmitPod(activePods, pod); !ok {
+				kl.rejectPod(pod, reason, message)
+				continue
+			}
 		}
-		kl.podManager.AddPod(pod)
 		mirrorPod, _ := kl.podManager.GetMirrorPodByPod(pod)
 		kl.dispatchWork(pod, kubetypes.SyncPodCreate, mirrorPod, start)
 		kl.probeManager.AddPod(pod)