Add more log messages for sandbox restarts

pkg/kubelet/kuberuntime/kuberuntime_manager.go

@@ -387,6 +387,7 @@ type podContainerSpecChanges struct {
 // (changed, new attempt, original sandboxID if exist).
 func (m *kubeGenericRuntimeManager) podSandboxChanged(pod *api.Pod, podStatus *kubecontainer.PodStatus) (changed bool, attempt uint32, sandboxID string) {
 	if len(podStatus.SandboxStatuses) == 0 {
+		glog.V(2).Infof("No sandbox for pod %q can be found. Need to start a new one", format.Pod(pod))
 		return true, 0, ""
 	}
 
@@ -400,12 +401,14 @@ func (m *kubeGenericRuntimeManager) podSandboxChanged(pod *api.Pod, podStatus *k
 	// Needs to create a new sandbox when readySandboxCount > 1 or the ready sandbox is not the latest one.
 	sandboxStatus := podStatus.SandboxStatuses[0]
 	if readySandboxCount > 1 || sandboxStatus.GetState() != runtimeApi.PodSandBoxState_READY {
+		glog.V(2).Infof("No ready sandbox for pod %q can be found. Need to start a new one", format.Pod(pod))
 		return true, sandboxStatus.Metadata.GetAttempt() + 1, sandboxStatus.GetId()
 	}
 
 	// Needs to create a new sandbox when network namespace changed.
 	if sandboxStatus.Linux != nil && sandboxStatus.Linux.Namespaces.Options != nil &&
 		sandboxStatus.Linux.Namespaces.Options.GetHostNetwork() != kubecontainer.IsHostNetworkPod(pod) {
+		glog.V(2).Infof("Sandbox for pod %q has changed. Need to start a new one", format.Pod(pod))
 		return true, sandboxStatus.Metadata.GetAttempt() + 1, ""
 	}