Scheduling: How Kubernetes Places Pods on Nodes

You kubectl apply a Deployment, and thirty seconds later all three replicas are Running. Then one day they aren't. One replica is stuck in Pending: "0/4 nodes are available: 1 node had untolerated taint, 3 nodes didn't match Pod's node affinity/selector." The scheduler couldn't find a node that satisfied the Pod's constraints.

kube-scheduler is the control plane component behind every placement decision. Understanding how it works is the key to understanding why Pods end up where they do. Scheduling falls within the KCNA Kubernetes Fundamentals domain, which accounts for 46% of the exam.