Monitoring with kubectl top and Metrics Server

kubectl top pod failing with "Error from server (ServiceUnavailable)" is one of the first things that surprises people in a fresh cluster. The command depends on Metrics Server, which isn't installed by default in most distributions. On the CKAD exam it's there, but knowing why it needs to be there, and what the numbers actually mean, separates candidates who can use it from candidates who can only recite what it does.

This article covers the resource metrics pipeline from kubelet to kubectl top, how to install and verify Metrics Server, and every kubectl top flag you'll reach for in the exam and in production spot-checks.