Kubernetes components overview

Kubernetes is a popular open-source container orchestration platform that is commonly used for managing containerized applications. It automates various tasks such as deploying, scaling, and managing containerized applications. In this blog post, we will provide an overview of the main components of Kubernetes.

Kubernetes Components

Master Node Components

The master components of Kubernetes are responsible for managing the overall state of the cluster. It orchestrates the deployment and scaling of containerized applications. The master components include:

API Server

The API server is the central management entity of Kubernetes. It serves all the RESTful API calls that are made to the cluster. It is responsible for validating and processing API requests and updating the state of the cluster.

etcd

etcd is a distributed key-value store that is used to store the configuration data of the cluster. It is used as the backing store for all cluster data.

Controller Manager

The controller manager is responsible for managing various controllers that regulate the state of the cluster. It ensures that the desired state of the cluster matches the actual state.

Scheduler

The scheduler is responsible for scheduling the deployment of containers on the worker nodes. It selects the best node for a given pod and ensures that the required resources are available before scheduling the pod.

Worker Node Components

The node components run on each worker node in the cluster. They are responsible for managing the containers and the associated resources on the node. The node components include:

Kubelet

Kubelet is the primary agent that runs on each worker node. It is responsible for managing the state of the containers running on the node. It communicates with the API server to receive instructions on which containers to run and ensures that the containers are healthy.

kube-proxy

kube-proxy is responsible for managing the network connectivity between different pods and services in the cluster. It ensures that each pod can communicate with other pods and external services.

Container Runtime

The container runtime is responsible for running the containers. Kubernetes supports various container runtimes, including Docker, containerd, and CRI-O.

Component name	Control plane, worker node, or client
Kubeadm	Admin tool
Kube-apiserver	Control plane (master node)
Etcd	Control plane (master node)
Kube-scheduler	Control plane (master node)
Kube-controller-manager	Control plane (master node)
Kubelet	Worker node
Kube-proxy	Worker node
Container Engine	Worker node
kubectl	Client

Interacting with the API server

CLI: kubectl
API: https://kubernetes.io/docs/concepts/overview/kubernetes-api

Basic usage of kubectl & kubeadm

kubectl create
kubectl get
kubectl apply
kubectl describe
kubectl exec
kubectl run

kubeadm config
kubeadm init
kubeadm join
kubeadm reset

Frequently used API Resources Shortname

NAME	SHORTNAMES
configmaps	cm
endpoints	ep
events	ev
namespaces	ns
nodes	no
persistentvolumeclaims	pvc
persistentvolumes	pv
pods	po
replicationcontrollers	rc
serviceaccounts	sa
services	svc
daemonsets	ds
deployments	deploy
replicasets	rs
cronjobs	cj
networkpolicies	netpol
podsecuritypolicies	psp

API Resources

kubectl api-resources --sort-by name -o wide

NAME	SHORTNAMES	APIVERSION	NAMESPACED	KIND
bindings		v1	TRUE	Binding
componentstatuses	cs	v1	FALSE	ComponentStatus
configmaps	cm	v1	TRUE	ConfigMap
endpoints	ep	v1	TRUE	Endpoints
events	ev	v1	TRUE	Event
limitranges	limits	v1	TRUE	LimitRange
namespaces	ns	v1	FALSE	Namespace
nodes	no	v1	FALSE	Node
persistentvolumeclaims	pvc	v1	TRUE	PersistentVolumeClaim
persistentvolumes	pv	v1	FALSE	PersistentVolume
pods	po	v1	TRUE	Pod
podtemplates		v1	TRUE	PodTemplate
replicationcontrollers	rc	v1	TRUE	ReplicationController
resourcequotas	quota	v1	TRUE	ResourceQuota
secrets		v1	TRUE	Secret
serviceaccounts	sa	v1	TRUE	ServiceAccount
services	svc	v1	TRUE	Service
mutatingwebhookconfigurations		admissionregistration.k8s.io/v1	FALSE	MutatingWebhookConfiguration
validatingwebhookconfigurations		admissionregistration.k8s.io/v1	FALSE	ValidatingWebhookConfiguration
customresourcedefinitions	crd,crds	apiextensions.k8s.io/v1	FALSE	CustomResourceDefinition
apiservices		apiregistration.k8s.io/v1	FALSE	APIService
controllerrevisions		apps/v1	TRUE	ControllerRevision
daemonsets	ds	apps/v1	TRUE	DaemonSet
deployments	deploy	apps/v1	TRUE	Deployment
replicasets	rs	apps/v1	TRUE	ReplicaSet
statefulsets	sts	apps/v1	TRUE	StatefulSet
tokenreviews		authentication.k8s.io/v1	FALSE	TokenReview
localsubjectaccessreviews		authorization.k8s.io/v1	TRUE	LocalSubjectAccessReview
selfsubjectaccessreviews		authorization.k8s.io/v1	FALSE	SelfSubjectAccessReview
selfsubjectrulesreviews		authorization.k8s.io/v1	FALSE	SelfSubjectRulesReview
subjectaccessreviews		authorization.k8s.io/v1	FALSE	SubjectAccessReview
horizontalpodautoscalers	hpa	autoscaling/v2	TRUE	HorizontalPodAutoscaler
cronjobs	cj	batch/v1	TRUE	CronJob
jobs		batch/v1	TRUE	Job
certificatesigningrequests	csr	certificates.k8s.io/v1	FALSE	CertificateSigningRequest
leases		coordination.k8s.io/v1	TRUE	Lease
bgpconfigurations		crd.projectcalico.org/v1	FALSE	BGPConfiguration
bgppeers		crd.projectcalico.org/v1	FALSE	BGPPeer
blockaffinities		crd.projectcalico.org/v1	FALSE	BlockAffinity
caliconodestatuses		crd.projectcalico.org/v1	FALSE	CalicoNodeStatus
clusterinformations		crd.projectcalico.org/v1	FALSE	ClusterInformation
felixconfigurations		crd.projectcalico.org/v1	FALSE	FelixConfiguration
globalnetworkpolicies		crd.projectcalico.org/v1	FALSE	GlobalNetworkPolicy
globalnetworksets		crd.projectcalico.org/v1	FALSE	GlobalNetworkSet
hostendpoints		crd.projectcalico.org/v1	FALSE	HostEndpoint
ipamblocks		crd.projectcalico.org/v1	FALSE	IPAMBlock
ipamconfigs		crd.projectcalico.org/v1	FALSE	IPAMConfig
ipamhandles		crd.projectcalico.org/v1	FALSE	IPAMHandle
ippools		crd.projectcalico.org/v1	FALSE	IPPool
ipreservations		crd.projectcalico.org/v1	FALSE	IPReservation
kubecontrollersconfigurations		crd.projectcalico.org/v1	FALSE	KubeControllersConfiguration
networkpolicies		crd.projectcalico.org/v1	TRUE	NetworkPolicy
networksets		crd.projectcalico.org/v1	TRUE	NetworkSet
endpointslices		discovery.k8s.io/v1	TRUE	EndpointSlice
events	ev	events.k8s.io/v1	TRUE	Event
flowschemas		flowcontrol.apiserver.k8s.io/v1beta3	FALSE	FlowSchema
prioritylevelconfigurations		flowcontrol.apiserver.k8s.io/v1beta3	FALSE	PriorityLevelConfiguration
ingressclasses		networking.k8s.io/v1	FALSE	IngressClass
ingresses	ing	networking.k8s.io/v1	TRUE	Ingress
networkpolicies	netpol	networking.k8s.io/v1	TRUE	NetworkPolicy
runtimeclasses		node.k8s.io/v1	FALSE	RuntimeClass
poddisruptionbudgets	pdb	policy/v1	TRUE	PodDisruptionBudget
clusterrolebindings		rbac.authorization.k8s.io/v1	FALSE	ClusterRoleBinding
clusterroles		rbac.authorization.k8s.io/v1	FALSE	ClusterRole
rolebindings		rbac.authorization.k8s.io/v1	TRUE	RoleBinding
roles		rbac.authorization.k8s.io/v1	TRUE	Role
priorityclasses	pc	scheduling.k8s.io/v1	FALSE	PriorityClass
csidrivers		storage.k8s.io/v1	FALSE	CSIDriver
csinodes		storage.k8s.io/v1	FALSE	CSINode
csistoragecapacities		storage.k8s.io/v1	TRUE	CSIStorageCapacity
storageclasses	sc	storage.k8s.io/v1	FALSE	StorageClass
volumeattachments		storage.k8s.io/v1	FALSE	VolumeAttachment

Kubernetes components overview