title: count k8s cluster cpu/memory usage with prometheus
body: <p>I want to count k8s cluster cpu/memory usage (not k8s pod usage) with prometheus, so that i can show in grafana.</p>
  
  <p>I use <code>sum (container_memory_usage_bytes{id="/"})</code> to get k8s cluster used memory, and <code>topk(1, sum(kube_node_status_capacity_memory_bytes) by (instance))</code> to get whole k8s cluster memory, but they can not divide since <code>topk</code> function does not return value but vector.</p>
  
  <p>How can i do this?</p>