Kubernetes Architecture

Kubernetes have Master and Worker nodes, we can also say them as Control plane and Data plane respectively. Nodes run the pods that are the components of application workloads and Master node controls the worker nodes and the pods in cluster .

There are some components of Kubernetes which are divided among worker nodes and control plane you can see below in the picture.

Components On Control Plane

kube-apiserver : The API server is a component of the Kubernetes control plane that exposes the Kubernetes API. The API server is the front end for the Kubernetes control plane. for eg: Its like receptionist of an hotel, you need to call receptionist for food order, laundry and etc . you can not directly go to the kitchen and ask chef to prepare order for you .

etcd : A key-value database that contains data about your cluster state and configuration,It is a highly available and consistent data store that provides a reliable way for the various components of Kubernetes to store and retrieve data about the cluster. Etcd is fault tolerant and distributed.

scheduler : This component is responsible for scheduling pods on specific nodes according to automated workflows and user defined conditions, which can include resource requests, concerns like affinity and taints or tolerations, priority, persistent volumes (PV), and more.

kube-controller-manager : Control plane component that runs controller processes. Logically, each controller is a separate process, but to reduce complexity, they are all compiled into a single binary and run in a single process.

There are many different types of controllers. Some examples of them are:

• Node controller: Responsible for noticing and responding when nodes go down.
• Job controller: Watches for Job objects that represent one-off tasks, then creates Pods to run those tasks to completion.
• ServiceAccount controller: Create default ServiceAccounts for new namespaces.

Components On Worker nodes

kubelet : Its an agent that makes sure the containers are running inside pods as per the PodSpecs . kubelet takes the set of PodSpecs, that are provided through various mechanisms and ensures that the containers described in those PodSpecs are running and healthy, The kubelet doesn’t manage containers which were not created by Kubernetes.

kube-proxy : kube-proxy is a network proxy which runs on each node in your cluster, kube-proxy maintains network rules on nodes, These network rules allow network communication to your Pods from network sessions inside or outside of your cluster.

container runtime : A fundamental component that empowers Kubernetes to run containers effectively. It is responsible for managing the execution and lifecycle of containers within the Kubernetes environment. Kubernetes supports container runtimes such as containerd, CRI-O, and any other implementation of the Kubernetes CRI (Container Runtime Interface).