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Lesson 02 / 15
Architecture: control plane vs. nodes
Every cluster splits into two kinds of machines: the control plane (the brains) and worker nodes (the muscle, where your actual app containers run).
Everything flows through the API server. Nothing else talks to etcd or the nodes directly.
| Component | Job |
|---|---|
| API server | The front door — every kubectl command, every controller, everyone talks to this |
| etcd | The cluster's database — the entire desired & actual state lives here |
| Scheduler | Decides which node a new pod should run on, based on resources and constraints |
| Controller manager | Runs the reconciliation loops — "actual replicas = 2, desired = 4, make 2 more" |
| kubelet | Runs on every node — talks to the API server, starts/stops containers as instructed |
| Container runtime | containerd or CRI-O — actually pulls images and runs containers, kubelet's helper |
Try it yourselfIf you have a cluster handy (even a local one like minikube or kind), run
kubectl get nodes and kubectl cluster-info. You're looking at exactly the two halves in the diagram above.