Understanding memory usage for "kubectl top node"

Question

How do I interpret the memory usage returned by "kubectl top node". E.g. if it returns:

NAME                   CPU(cores)   CPU%      MEMORY(bytes)   MEMORY%
ip-XXX.ec2.internal    222m         11%       3237Mi          41%
ip-YYY.ec2.internal    91m          9%        2217Mi          60%

By comparison, if I look in the Kubernetes dashboard for the same node, I get: Memory Requests: 410M / 7.799 Gi

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**kubernetes dashboard**

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How do I reconcile the difference?

Teresita

Do you have to use heapster? I have heapster running but kubectl top node shows me "error: metrics not available yet" – Bullhorn

Answer 1

kubectl top node is reflecting the actual usage to the VM(nodes), and k8s dashboard is showing the percentage of limit/request you configured.

E.g. Your EC2 instance has 8G memory and you actually use 3237MB so it's 41%. In k8s, you only request 410MB(5.13%), and have a limit of 470MB memory. This doesn't mean you only consume 5.13% memory, but the amount configured.

  Namespace         Name                                CPU Requests    CPU Limits  Memory Requests Memory Limits
  ---------         ----                                ------------    ----------  --------------- -------------
  default           kube-lego                           20m (2%)    0 (0%)      0 (0%)      0 (0%)
  default           mongo-0                             100m (10%)  0 (0%)      0 (0%)      0 (0%)
  default           web                                 100m (10%)  0 (0%)      0 (0%)      0 (0%)
  kube-system       event-exporter-                     0 (0%)      0 (0%)      0 (0%)      0 (0%)
  kube-system       fluentd-gcp-v2.0-z6xh9              100m (10%)  0 (0%)      200Mi (11%) 300Mi (17%)
  kube-system       heapster-v1.4.0-3405140848-k6cm9    138m (13%)  138m (13%)  301456Ki (17%)  301456Ki (17%)
  kube-system       kube-dns-3809445927-hn5xk           260m (26%)  0 (0%)      110Mi (6%)  170Mi (9%)
  kube-system       kube-dns-autoscaler-38801           20m (2%)    0 (0%)      10Mi (0%)   0 (0%)
  kube-system       kube-proxy-gke-staging-default-     100m (10%)  0 (0%)      0 (0%)      0 (0%)
  kube-system       kubernetes-dashboard-1962351        100m (10%)  100m (10%)  100Mi (5%)  300Mi (17%)
  kube-system       l7-default-backend-295440977        10m (1%)    10m (1%)    20Mi (1%)   20Mi (1%)

Here you see many pods with 0 request/limit means unlimited, which didn't count in k8s dashboard but definitely consume memory.

Sum up the memory request/limit you'll find they match k8s dashboard.

Wellknit

What about CPU% in kubectl top nodes does it show actually CPU usage of VM (node)? And does any API exists to get this nice % values? – Geddes

Same thing. kubectl top nodes shows actually CPU usage of VM(node). And I think k8s doesn't provide this kind of API for now. – Wellknit

@AlejandroPedraza kubectl describe nodes – Wellknit

Useful: kubernetes.io/docs/tasks/configure-pod-container/… – Enthusiasm