Kubernetes Architecture
The control plane and node components that make Kubernetes a self-healing system.
Kubernetes is a declarative, reconciliation-based system: you submit the desired state, and controllers continuously work to make reality match. It splits into a control plane and worker nodes.
Control plane:
- API server — the front door; everything goes through it
- etcd — the cluster’s key/value state store
- scheduler — assigns Pods to nodes
- controller manager — runs reconciliation loops (e.g. keep N replicas)
Each node:
- kubelet — starts/monitors Pods on the node
- container runtime — runs the containers (containerd)
- kube-proxy — implements Service networking
graph TD
subgraph Control Plane
API["API server"] --> ETCD["etcd"]
API --> SCH["scheduler"]
API --> CM["controller manager"]
end
API --> K1["kubelet (node 1)"]
API --> K2["kubelet (node 2)"]
K1 --> P1["Pods"]
K2 --> P2["Pods"] - Name the four control-plane components and one responsibility of each.
- Explain what kubelet and kube-proxy do on a worker node.
- Describe the reconciliation loop using “desired 3 replicas” as an example.
- Why does everything go through the API server?
Cheat Sheet▾
| Component | Role |
|---|---|
| API server | Front door for all requests |
| etcd | Cluster state store |
| scheduler | Places Pods on nodes |
| controller manager | Reconciliation loops |
| kubelet | Runs Pods on a node |
| container runtime | Runs containers (containerd) |
| kube-proxy | Service networking |
Common Interview Questions▾
Describe Kubernetes architecture.
A control plane (API server, etcd, scheduler, controller manager) manages desired state; worker nodes run kubelet, a container runtime, and kube-proxy to execute workloads. Controllers reconcile actual state to desired state.
What does the scheduler do?
It watches for unscheduled Pods and assigns each to a suitable node based on resource requests, constraints, affinity, and taints/tolerations.
What is etcd's role?
It’s the consistent key/value store holding all cluster state — the single source of truth the API server reads from and writes to.