kubectl
=========
###### tags: `kubernetes`

<kbd>kubectl</kbd> allows you to run commands against Kubernetes clusters.You can use kubectl to deploy applications, inspect and manage cluster resources, and view logs.

## how to install

curl -LO "https://dl.k8s.io/release/v1.26.4/bin/darwin/amd64/kubectl"
chmod +x ./kubectl
sudo mv ./kubectl /usr/local/bin/kubectl
sudo chown root: /usr/local/bin/kubectl
alias k=kubectl

## useful "imperative" command lines
> ==**explicit instructions**==

### management

kubectl version -o json
kubectl cluster-info
kubectl get nodes

### config
:::info
The loading order follows these rules
1. `--kubeconfig` flag
2. `$KUBECONFIG` environment variable
3. `${HOME}/.kube/config` is used
:::

kubectl config view
kubectl config get-clusters
kubectl config get-contexts
kubectl config get-users
kubectl config use-context minikube
kubectl config set-context $(kubectl config current-context) --namespace=dev

### workload

kubectl api-versions
kubectl api-resources
kubectl get all -A

kubectl get pods -n whale \
-l "app=blue-app" \
-o jsonpath="{.items[0].metadata.name}"

### monitor

$ k top node

NAME           CPU(cores)   CPU%   MEMORY(bytes)   MEMORY%   
controlplane   353m         0%     1060Mi          0%        
node01         22m          0%     322Mi           0%        

$ k top po

NAME       CPU(cores)   MEMORY(bytes)   
elephant   20m          32Mi            
lion       1m           18Mi            
rabbit     132m         252Mi           

### others

kubectl auth can-i get pods --all-namespaces
kubectl auth can-i get pods -n default
kubectl auth can-i create pods
kubectl auth can-i delete pods
kubectl auth can-i create deployments --as=dev-user
kubectl auth can-i create pods --as=dev-user --namespace=test
kubectl auth can-i list nodes --as=bruce

# list 所有權限
kubectl auth can-i --list --as=jenkins

kubectl set image deployment/nginx nginx=nginx:1.18

kubectl label pod/meesaging tier=message --overwrite

## "declarative" command
> ==**descibe outcome**==
+ create the object using `kubectl apply -f` command.

## JSON path

k get no -o custom-columns=NODE:.metadata.name,CPU:.status.capacity.cpu
k get po -o jsonpath='{.items[0].spec.containers[0].image}'
k get no -o jsonpath='{.items[*].metadata.name}{"\n"}{.items[*].status.capacity.cpu}'
k get no --sort-by=.status.capacity.cpu

kubectl -n admin2406 get deployment -o custom-columns=DEPLOYMENT:.metadata.name,CONTAINER_IMAGE:.spec.template.spec.containers[].image,READY_REPLICAS:.status.readyReplicas,NAMESPACE:.metadata.namespace --sort-by=.metadata.name > /opt/admin2406_data