Quality of service assures that a pod can access the appropriate resources, but the philosophy doesn't take the pod's importance into consideration. To be more precise, QoS only comes into play when a pod is scheduled, not during scheduling. Therefore, we need to introduce an orthogonal feature to denote the pod's criticality or importance.
Before 1.11, making a pod's criticality visible to Kubernetes was done by putting the pod in the kube-system namespace and annotating it with scheduler.alpha.kubernetes.io/critical-pod, which is going to be deprecated in the newer version of Kubernetes. See https://kubernetes.io/docs/tasks/administer-cluster/guaranteed-scheduling-critical-addon-pods/ for more information. ...
