CKAD 1 | Core Concepts

Basic Creation commands

• create pod

kubectl run podName --image=imageName --env=KEY=VALUE --labels=key=value --port=PortNum

• delete pod

kubectl delete po podName

• create deployment

kubectl create deployment depName --image=imageName -r replicaCount --port=PortNum

• configMap

kubectl create cm cmName --from-literal=key=value

• service

kubectl create svc clusterip svcName --tcp=sourceIP:targetIP

• secret

kubectl create secret generic secretName --from-literal=key=value

• apply file

kubectl apply -f fileName

• bind secret and configmap

kubectl set env --from=secret/secretName --from=configmap/cmName objectType/objectName

• update resource limits

kubectl set resources objectType objectName --limits=cpu=cpuQuotaUpperBound,memory=memQuotaUpperBound --requests=cpu=cpuQuotaLowerBound,memory=memQuotaLowerBound

• label pod

kubectl label pods podName key=value --overwrite

• update replicas

kubectl scale --replicas=repValue deployment/deploymentName

• execute on pod

kubectl exec podName -c containerName -- command

• unschedule node

kubectl cordon nodeName

• node for maintaince

kubectl drain nodeName

• bring node back

kubectl uncordon nodeName

• taint node

kubectl taint node nodeName key=value:NoSchedule-

• edit with YAML

kubectl edit objectType/objectName -o yaml 

• force replace YAML to update (don’t need to specify the object)

kubectl replace -f fileName --force

• get pod logs

kubectl logs podName -n namespace

Commands and Arguments

• Update pod container commands

apiVersion: v1
kind: Pod
metadata:
    name: podName
spec:
    containers:
    - name: containerName
      image: containerImage
      command:
      - commands
      - to
      - be
      - executed
      args:
      - command
      - arguments

Can also be written as,

apiVersion: v1
kind: Pod
metadata:
    name: podName
spec:
    containers:
    - name: containerName
      image: containerImage
      command: ["commands", "to", "be", "executed"]
      args: ["command", "arguments"]

• ENTRYPOINT commands in the Dockerfile will be override by pod defination

• We can only specify the argument to use the commands in Dockerfile by default

Environment Variables

apiVersion: v1
kind: Pod
metadata:
    name: podName
spec:
    containers:
    - name: containerName
      image: containerImage
      env:
      - name: ENVVARNAME
        value: envVarValue

Configmap

• Create configmap by,

$ kubectl create cm configMapName --from-literal=key=val

• Bind pod with one key in configMap

apiVersion: v1
kind: Pod
metadata: 
  name: podName
spec:
  containers:
    - name: containerName
      image: containerImage
      env:
        - name: KEY
          valueFrom:
            configMapKeyRef:
              name: cmName
              key: KEY

• Bind pod with all Keys in configMap

apiVersion: v1
kind: Pod
metadata: 
  name: podName
spec:
  containers:
    - name: containerName
      image: containerImage
      envFrom:
        - configMapRef:
            name: cmName

Secrets

• Create a serect: must use generic

$ kubectl create secret generic secretName --from-literal=KEY=value

• Bind pod with secret

apiVersion: v1
kind: Pod
metadata: 
  name: podName
spec:
  containers:
    - name: containerName
      image: containerImage
      envFrom:
        - secretRef:
            name: secretName

Pod Execution

• One command

$ kubectl exec -it podName -- command

• Get shell

$ kubectl exec -it podName -- sh

Security Context

• Specify user for all containers in a pod

apiVersion: v1
kind: Pod
metadata: 
  name: podName
spec:
  securityContext:
    runAsUser: userID
  containers:
    - name: containerName
      image: containerImage

• Specify user for one container

apiVersion: v1
kind: Pod
metadata: 
  name: podName
spec:
  containers:
    - name: containerName
      image: containerImage
      securityContext:
        runAsUser: userID

• Grant container privileges of CAP_SYS_TIME

apiVersion: v1
kind: Pod
metadata: 
  name: podName
spec:
  containers:
    - name: containerName
      image: containerImage
      securityContext:
        capabilities:
          add: ["SYS_TIME"]

Resources

• Set memory limitations

apiVersion: v1
kind: Pod
metadata: 
  name: podName
spec:
  containers:
    - name: containerName
      image: containerImage
      resources:
        limits:
          memory: 10Mi
        requests:
          memory: 5Mi

Node Affinity

• Show labels

$ kubectl get node --show-labels

• Set a label

$ kubectl set node nodeName key=value