Kubernetes Architecture

The control plane and node components that make up a Kubernetes cluster.

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Kubernetes Architecture

A Kubernetes cluster consists of two types of resources: the Control Plane and Nodes.

Worker Node 2

Worker Node 1

Control Plane

kube-apiserver

etcd

kube-scheduler

kube-controller-manager

cloud-controller-manager

kubelet

kube-proxy

Container Runtime

Pod 1

Pod 2

kubelet

kube-proxy

Container Runtime

Pod 3

1. Control Plane

The “brain” of the cluster. It makes global decisions (like scheduling) and detects/responds to cluster events.

  • kube-apiserver: The front end for the Kubernetes control plane. It exposes the API.
  • etcd: Consistent and highly-available key-value store used as Kubernetes’ backing store for all cluster data.
  • kube-scheduler: Watches for newly created Pods with no assigned node, and selects a node for them to run on.
  • kube-controller-manager: Runs controller processes (like Node Controller, Job Controller).
  • cloud-controller-manager: Links your cluster into your cloud provider’s API.

2. Nodes

The worker machines that run applications.

  • kubelet: An agent that runs on each node in the cluster. It ensures that containers are running in a Pod.
  • kube-proxy: A network proxy that runs on each node, maintaining network rules and performing connection forwarding.
  • Container Runtime: The software responsible for running containers (e.g., Docker, containerd, CRI-O).

3. Objects

  • Pod: The smallest deployable units of computing that you can create and manage in Kubernetes.
  • Service: An abstract way to expose an application running on a set of Pods as a network service.
  • Volume: A directory containing data, accessible to the containers in a Pod.
  • Namespace: Virtual clusters backed by the same physical cluster.