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Interactive Explainer

Kubernetes Cluster Architecture: Control Plane & Nodes

Understanding the distributed decision-making system that powers container orchestration: control plane, nodes, etcd, and the reconciliation loop.

How this might come up in interviews

System design interviews for platform/infra roles. "Design a self-healing deployment system." Also common in Kubernetes admin/CKA prep.

Common questions:

  • What happens when you run kubectl apply?
  • What is the difference between a Deployment and a ReplicaSet?
  • How does Kubernetes handle a node failure?
  • What would happen if etcd went down?
  • Walk me through the kube-scheduler decision process.

Strong answer: Mentions etcd quorum requirements. Knows the API server is stateless. Can explain why self-healing works (ReplicaSet controller watches pod count). Mentions that managed K8s hides the control plane.

Red flags: Says "kubectl talks to the node directly". Thinks Docker is the container runtime. Confused about who schedules vs who runs pods.

Key takeaways

  • Control plane = brain (API server is the only entry point)
  • etcd stores ALL cluster state — losing it means losing your cluster
  • Reconciliation loop: desired state vs actual state is the core K8s idea
  • Worker nodes run your workloads — kubelet is the node agent
  • Every kubectl command hits kube-apiserver first

Related concepts

Explore topics that connect to this one.

  • etcd: Kubernetes Source of Truth
  • kube-apiserver Internals
  • kubernetes evolution

Suggested next

Often learned after this topic.

etcd: Kubernetes Source of Truth

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etcd: Kubernetes Source of Truth

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