kubelet: record an event with a clear reason on host port conflict

Currently, kubelet silently ignores pods that caused host port conflict. This
commit surfaces the error by recording an event.

It also makes sure that kubelet iterates through the pods in the order of the
creation timestamp, which ensures that pods created later are ignored on
conflict.

pkg/kubelet/kubelet.go

@@ -1378,15 +1378,35 @@ func updateBoundPods(changed []api.BoundPod, current []api.BoundPod) []api.Bound
 	return updated
 }
 
+type podsByCreationTime []api.BoundPod
+
+func (s podsByCreationTime) Len() int {
+	return len(s)
+}
+
+func (s podsByCreationTime) Swap(i, j int) {
+	s[i], s[j] = s[j], s[i]
+}
+
+func (s podsByCreationTime) Less(i, j int) bool {
+	return s[i].CreationTimestamp.Before(s[j].CreationTimestamp)
+}
+
 // filterHostPortConflicts removes pods that conflict on Port.HostPort values
 func filterHostPortConflicts(pods []api.BoundPod) []api.BoundPod {
 	filtered := []api.BoundPod{}
 	ports := map[int]bool{}
 	extract := func(p *api.Port) int { return p.HostPort }
+
+	// Respect the pod creation order when resolving conflicts.
+	sort.Sort(podsByCreationTime(pods))
+
 	for i := range pods {
 		pod := &pods[i]
 		if errs := validation.AccumulateUniquePorts(pod.Spec.Containers, ports, extract); len(errs) != 0 {
 			glog.Warningf("Pod %q: HostPort is already allocated, ignoring: %v", GetPodFullName(pod), errs)
+			record.Eventf(pod, "hostPortConflict", "Cannot start the pod due to host port conflict.")
+			// TODO: Set the pod status to fail.
 			continue
 		}
 		filtered = append(filtered, *pod)