kubectl basics ¶

Scenario: get to know how to operate Kubernetes cluster using kubectl.

via API
via kubectl
via Dashboard

Demo:

Check current kubeconfig file ¶

Use the kubectl config command to get current context of configuration file.

echo $KUBECONFIG
kubectl config view
kubectl config get-contexts

Get resource list ¶

Get a complete list of supported resources

kubectl api-resources

Get cluster status ¶

Kubernetes control plane is running at https://<control_plane_ip>:6443

CoreDNS is running at https://<control_plane_ip>:6443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy

kubectl cluster-info
kubectl cluster-info dump

Display resources ¶

Use kubectl get --help to get examples of displaying one or many resources.

Get health status of control plane.

kubectl get componentstatuses
kubectl get cs

Result

NAME                 STATUS    MESSAGE                         ERROR
etcd-0               Healthy   {"health":"true","reason":""}   
scheduler            Healthy   ok                              
controller-manager   Healthy   ok

Get node status and details ¶

kubectl get nodes
kubectl get nodes -o wide
kubectl describe node cka001

Use command kubectl create --help to get examples of creating resources.

Create namespace ¶

kubectl create namespace --help
kubectl create namespace my-namespace

Information

Namespace is a cluster, which includes services. Service may be on a node, may be not.

Create deployment ¶

Create Deployment on the namespace.

kubectl -n my-namespace create deployment my-busybox \
  --image=busybox \
  --replicas=3 \
  --port=5701

Create ClusterRole ¶

kubectl create clusterrole --help

kubectl create clusterrole pod-creater \
  -n my-namespace \
  --verb=create \
  --resource=deployment \
  --resource-name=my-busybox

Create ServiceAccount ¶

kubectl create serviceaccount --help
kubectl -n my-namespace create serviceaccount my-service-account

Create RoleBinding ¶

Note

RoleBinding can reference a Role in the same namespace or a ClusterRole in the global namespace.

kubectl create rolebinding --help

kubectl create rolebinding NAME \
  --clusterrole=NAME|--role=NAME \
  [--user=username] \
  [--group=groupname] \
  [--serviceaccount=namespace:serviceaccountname] \
  [--dry-run=server|client|none]

kubectl create rolebinding my-admin \
  --clusterrole=pod-creater \
  --serviceaccount=my-namespace:my-service-account

Use the proxy ¶

We can use kubectl proxy command to open a tunnel to the API server and make it available locally - usually on localhost:8001 / 127.0.0.1:8001. When I want to explore the API, this is an easy way to gain access.

Run the command kubectl proxy & and open http://localhost:8001/api/v1 in browser. Just opening http://localhost:8001 will return an error because we are only allowed to access certain parts of the API. Hence the API path is important

kubectl proxy &

Output

[1] 102358
Starting to serve on 127.0.0.1:8001

Example, get available API groups and so on via below link:

http://127.0.0.1:8001/
http://127.0.0.1:8001/api/v1
http://127.0.0.1:8001/api/v1/namespaces
http://127.0.0.1:8001/api/v1/namespaces/default
http://127.0.0.1:8001/api/v1/namespaces/sock-shop/pods

Access as application ¶

If we access kubernetes as an application rather than an administrator, we cannot use the kubectl. Instead of kubectl we can use the program curl. We have to send HTTP requests to the cluster. asking for the available nodes.

Make sure kubectl proxy is running and serving on http://localhost:8001/.

Execute command below with a -v=9 flag, it shows all the information needed.

kubectl get nodes

Go through the command's output and find the correct curl request below.

curl -v -XGET  \
  -H "Accept: application/json;as=Table;v=v1;g=meta.k8s.io,application/json;as=Table;v=v1beta1;g=meta.k8s.io,application/json" \
  -H "User-Agent: kubectl/v1.24.1 (linux/amd64) kubernetes/3ddd0f4" \
  'https://<control_plane_ip>/api/v1/nodes?limit=500'

Reference

*There is a forum-like page hosted by K8s with lots of information around kubectl and how to use it best. * Manage multiple clusters and multiple config files *kubectl command documentation * Shell autocompletion *kubectl cheat sheet * jsonpath in kubectl * kubectl