Metrics Server is a resource metrics for Kubernetes used for autoscaling (HPA/VPA). Official docs at https://github.com/kubernetes-sigs/metrics-server
It is installed by default. You can use it in command line with kubectl top:
# check resources usage on nodes
$ kubectl top nodes
NAME CPU(cores) CPU% MEMORY(bytes) MEMORY%
kubesol-dev2-c1 429m 21% 3064Mi 78%
kubesol-dev2-c2 530m 26% 2970Mi 75%
kubesol-dev2-c3 463m 23% 2866Mi 73%
kubesol-dev2-w1 640m 16% 4242Mi 53%
kubesol-dev2-w2 1248m 31% 4794Mi 60%
kubesol-dev2-w3 720m 18% 4391Mi 55%
# check resource usage in a namespace
$ kubectl -n kubernetes-dashboard top pods
NAME CPU(cores) MEMORY(bytes)
kubernetes-dashboard-api-5cd9f5b7-zz95t 2m 17Mi
kubernetes-dashboard-auth-856bf7d5df-gcxmm 1m 8Mi
kubernetes-dashboard-kong-65476f87d4-fggqz 5m 128Mi
kubernetes-dashboard-metrics-scraper-649fdcf444-r44nr 1m 21Mi
kubernetes-dashboard-web-6f96cf865c-d7jsh 0m 9Mi