what is it?
The core of Kubernetes’ control plane is the API server. The API server exposes an HTTP API that lets end users, different parts of your cluster, and external components communicate with one another.
The Kubernetes API lets you query and manipulate the state of API objects in Kubernetes (for example: Pods, Namespaces, ConfigMaps, and Events).
Most operations can be performed through the kubectl command-line interface or other command-line tools, such as kubeadm, which in turn use the API. However, you can also access the API directly using REST calls.
Consider using one of the client libraries if you are writing an application using the Kubernetes API.
– https://kubernetes.io/docs/concepts/overview/kubernetes-api/
why?
When you create a kubernetes resource you need to specify the apiVersion of the resource that you want to apply the resource against. With different versions of kubernetes and different CRD’s applied to your cluster keeping track of the version your cluster is setup to use can be a little trickey to remember.
The format of the apiVersion is apiGroup/version unless the resource is part of the core API group in which case youd don’t need to specify the api_group. So to figure out the apiVersion we’ll need to figure out both the api_group and version of a resource.
finding the group
To find get a list of installed api groups you can run the following command:
$ kubectl api-resourcesYou should get a output that looks similar to the following:
NAME SHORTNAMES APIGROUP NAMESPACED KIND
bindings true Binding
componentstatuses cs false ComponentStatus
configmaps cm true ConfigMap
endpoints ep true Endpoints
events ev true Event
limitranges limits true LimitRange
namespaces ns false Namespace
nodes no false Node
persistentvolumeclaims pvc true PersistentVolumeClaim
persistentvolumes pv false PersistentVolume
pods po true Pod
podtemplates true PodTemplate
replicationcontrollers rc true ReplicationController
resourcequotas quota true ResourceQuota
secrets true Secret
serviceaccounts sa true ServiceAccount
services svc true Service
challenges acme.cert-manager.io true Challenge
orders acme.cert-manager.io true Order
mutatingwebhookconfigurations admissionregistration.k8s.io false MutatingWebhookConfiguration
validatingwebhookconfigurations admissionregistration.k8s.io false ValidatingWebhookConfiguration
customresourcedefinitions crd,crds apiextensions.k8s.io false CustomResourceDefinition
apiservices apiregistration.k8s.io false APIService
controllerrevisions apps true ControllerRevision
daemonsets ds apps true DaemonSet
deployments deploy apps true Deployment
replicasets rs apps true ReplicaSet
statefulsets sts apps true StatefulSet
...If you look in the third column you can see a APIGROUP. For example if we needed to create a new resource for a daemonset we can see the apigroup is apps.
getting the api group version
Using the api group name we can grab the version with
$ kubectl api-versions | grep '^apps/'
apps/v1As you can see the apps/v1 contains the version required to create a daemonset.