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 |
Components at a glance
Network at a glance
Reference
- Kubernetes – An Enterprise Guide (Marc Boorshtein, Scott Surovich)
- Certified Kubernetes Administrator (CKA) Study Guide (Benjamin Muschko)
https://argo-cd.readthedocs.io/en/stable/understand_the_basics/
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