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_test.go

@@ -3086,3 +3086,38 @@ func TestPortForward(t *testing.T) {
 		t.Fatalf("stream: expected %v, got %v", e, a)
 	}
 }
+
+// Tests that upon host port conflict, the newer pod is removed.
+func TestFilterHostPortConflicts(t *testing.T) {
+	// Reuse the pod spec with the same port to create a conflict.
+	spec := api.PodSpec{Containers: []api.Container{{Ports: []api.Port{{HostPort: 80}}}}}
+	var pods = []api.BoundPod{
+		{
+			ObjectMeta: api.ObjectMeta{
+				UID:       "123456789",
+				Name:      "newpod",
+				Namespace: "foo",
+			},
+			Spec: spec,
+		},
+		{
+			ObjectMeta: api.ObjectMeta{
+				UID:       "987654321",
+				Name:      "oldpod",
+				Namespace: "foo",
+			},
+			Spec: spec,
+		},
+	}
+	// Make sure the BoundPods are in the reverse order of creation time.
+	pods[1].CreationTimestamp = util.NewTime(time.Now())
+	pods[0].CreationTimestamp = util.NewTime(time.Now().Add(1 * time.Second))
+	filteredPods := filterHostPortConflicts(pods)
+	if len(filteredPods) != 1 {
+		t.Fatalf("Expected one pod. Got pods %#v", filteredPods)
+	}
+	if filteredPods[0].Name != "oldpod" {
+		t.Fatalf("Expected pod %#v. Got pod %#v", pods[1], filteredPods[0])
+	}
+
+}