Control Plane vs. Worker Nodes: Key Architecture Components of a Kubernetes Cluster

Quick Answer: A cluster has a Control Plane (API Server, etcd, Scheduler, Controller Manager) and Worker Nodes (kubelet, kube-proxy, container runtime), plus optionally a cloud controller manager.

Detailed Answer:

Think of the cluster as a company: the Control Plane is headquarters (makes decisions) and Worker Nodes are the offices (do the actual work).

Control Plane:

• kube-apiserver: The front door — every kubectl command, every controller, every kubelet talks to the API server. It validates requests and persists state to etcd.
• etcd: The company's filing cabinet — a distributed key-value store holding all cluster state. If you lose etcd without a backup, you lose the cluster.
• kube-scheduler: HR that assigns new employees (pods) to offices (nodes) based on resource availability, affinity rules, and taints.
• kube-controller-manager: The management layer — runs dozens of controllers (Deployment controller, Node controller, etc.) that watch for drift and correct it.

Worker Nodes:

• kubelet: The office manager — receives pod assignments from the scheduler and ensures containers are running as specified.
• kube-proxy: The receptionist — maintains network rules so that Service traffic reaches the right pods.
• Container runtime: The actual infrastructure — containerd pulls images and runs containers.

Key Takeaway: Understanding which component does what lets you diagnose where in the chain something broke when things go wrong.

---