Kubernetes Architecture
To use Kubernetes effectively, you need to understand its architecture. A Kubernetes cluster consists of a control plane and worker nodes. Think of the control plane as the manager, and the nodes as the workers carrying out tasks.
Control Plane Components
The control plane manages the cluster. It includes:
- kube-apiserver: The frontend for Kubernetes; all commands go through it.
- etcd: A distributed key‑value store that holds cluster state and configuration.
- kube-scheduler: Assigns pods to worker nodes based on resource availability.
- kube-controller-manager: Runs controllers that handle tasks like node failures, replicas, etc.
Worker Node Components
Each worker node runs:
- kubelet: The agent that communicates with the control plane and runs containers.
- kube-proxy: Manages network rules and load‑balancing for services.
- Container runtime: The software that runs containers (e.g., Docker, containerd).
How They Work Together
1. You use
kubectl to send a command to the API server.2. The API server validates the request and stores it in etcd.
3. The scheduler finds a suitable node and assigns the pod.
4. The kubelet on that node receives the instruction and creates the container.
5. The controller manager monitors the state and ensures the desired number of replicas are running.
Visualizing the Architecture
Imagine a large office building:
- Control plane = CEO and management team (make decisions).
- Worker nodes = Departments where actual work happens.
- kubelet = Department managers who follow instructions.
Two Minute Drill
- Control plane: API server, etcd, scheduler, controller manager.
- Worker nodes: kubelet, kube-proxy, container runtime.
- API server is the central management point.
- etcd stores the cluster state.
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