## cheatsheet
* https://kubernetes.io/docs/user-guide/kubectl-cheatsheet/
* https://learnk8s.io/blog/kubectl-productivity/
* https://gist.github.com/so0k/42313dbb3b547a0f51a547bb968696ba
* https://speakerdeck.com/so0k/kubectl-tips-and-tricks
* https://github.com/dennyzhang/cheatsheet-kubernetes-A4
* https://medium.com/bitnami-perspectives/imperative-declarative-and-a-few-kubectl-tricks-9d6deabdde
* http://blog.kubernetes.io/2015/10/some-things-you-didnt-know-about-kubectl_28.html
* https://coreos.com/blog/kubectl-tips-and-tricks

## context, namespace
```
 get current context: kubectl config view -o=jsonpath='{.current-context}'
 get all contexts:  kubectl config get-contexts -o=name | sort -n
 get namesapce:  kubectl get namespaces -o=jsonpath='{range .items[*].metadata.name}{@}{"\n"}{end}'
 
kubectl config use-context <cluster_name_in_kubeconfig>
kubectl --context <context>

## set the namespace for the current context
kubectl config set-context gke_sandbox-co_us-west1-a_cka --namespace=kube-system
kubectl config set-context --current --namespace=kube-system
```
 
## generate yaml (dryrun)
* generate yaml: https://blog.heptio.com/using-kubectl-to-jumpstart-a-yaml-file-heptioprotip-6f5b8a63a3ea

```
kubectl run my-cool-app —-image=me/my-cool-app:v1 \
  -o yaml --dry-run > my-cool-app.yaml
kubectl run kuard --generator=run-pod/v1 --replicas=2 --image=gcr.io/kuar-demo/kuard-amd64:1 --dry-run -o yaml
kubectl create configmap ip-masq-agent --from-file=config --namespace=kube-system --dry-run -o yaml > ip-masq-agent.yaml
```
## API

```
kubectl get --raw /apis/apps/v1/namespaces/default/statefulsets/es-data/status |  jq -r '.spec.replicas'
```

* https://kubernetes.io/docs/tasks/administer-cluster/access-cluster-api/

## kubectl run
```
kubectl run kuard --generator=run-pod/v1 --replicas=2 --image=gcr.io/kuar-demo/kuard-amd64:1 
kubectl port-forward kuard 8080:8080

kubectl expose deployment kuard --type=LoadBalancer --port=80 --target-port=8080
```

## how it works
* https://github.com/jamiehannaford/what-happens-when-k8s

## secret
```
echo $(kubectl get secret/terraform -o jsonpath="{.data['terraform\.json']}" | base64 --decode)
```

## Play with jid and jq
* https://gist.github.com/so0k/42313dbb3b547a0f51a547bb968696ba
* https://kubernetes.io/docs/tasks/access-application-cluster/list-all-running-container-images/

```

grace=$(kubectl get po cassandra-0 -o=jsonpath=‘{.spec.terminationGracePeriodSeconds}’) 
grace=$(kubectl get sts -l component=elasticsearch,role=data -o jsonpath='{..terminationGracePeriodSeconds}'

kubectl get svc -l component=elasticsearch,role=client -o jsonpath='{..ip}'
kubectl get pods -o jsonpath="{..image}"
kubectl get pods -o jsonpath="{.items[*].spec.containers[*].image}"
kubectl get pods -o jsonpath='{.items[*].status.podIP}'
kubectl get pods -o jsonpath='{range .items[*]}{"\n"}{.metadata.name}{":\t"}{range .spec.containers[*]}{.image}{", "}{end}{end}'

kubectl get pods -o go-template --template="{{range .items}}{{range .spec.containers}}{{.image}} {{end}}{{end}}"

kubectl get po -o wide --sort-by=.spec.nodeName
```
## Get the pod cidr from nodes 

```
kubectl get nodes -o jsonpath='{.items[*].spec.podCIDR}' | tr " " "\n"
kubectl get nodes -o json | jq '.items[] | .spec'
kubectl get no -o go-template='{{range .items}}{{.spec.podCIDR}}{{"\n"}}{{end}}'
```

## Get the TCP LB port and IP
```
  EXT_IP="$(kubectl get svc hello-server -o=jsonpath='{.status.loadBalancer.ingress[0].ip}')"
  EXT_PORT=$(kubectl --namespace default get service hello-server -o=jsonpath='{.spec.ports[0].port}')
  echo "$EXT_IP:$EXT_PORT"
  [ "$(curl -s -o /dev/null -w '%{http_code}' "$EXT_IP:$EXT_PORT"/)" -eq 200 ] || exit 1
```
## loop over pods
```
kubectl get pods -o jsonpath --template='{range .items[*]}{.met
ata.name}{"\t"}{"\t"}{.spec.containers[0].image}{"\n"}{end}'
```
## export all
* https://github.com/kubernetes/kubernetes/issues/24873

## deployment

### rollout 
```
kubectl rollout pause deployment/hello
kubectl rollout status deployment/hello
# check the versions on pods
kubectl get pods -o jsonpath --template='{range .items[*]}{.metadata.name}{"\t"}{"\t"}{.spec.containers[0].image}{"\n"}{end}'
kubectl rollout resume deployment/hello
# roll back
kubectl rollout undo deployment/hello
```
## find top resource hungry pod
```
# cpu
kubectl top pods -A | sort --reverse --key 3 --numeric
# memory
kubectl top pods -A | sort --reverse --key 4 --numeric
# top 1
kubectl top pod | grep -v NAME | sort -k 3 -nr | awk -F ' ' 'NR==1{print $1}'
```