CKAD-Pod-Design.md

CKAD - Pod Design

Domain	Weight
Pod Design	20%
3.1 Understand Deployments and how to perform rolling updates
3.2 Understand Deployments and how to perform rollbacks
3.3 Understand Jobs and CronJobs
3.4 Understand how to use Labels, Selectors, and Annotations

3.1 Understand deployments and how to perform rolling update and rollbacks

https://kubernetes.io/docs/tutorials/kubernetes-basics/update/update-intro/

Deployments

https://kubernetes.io/docs/concepts/workloads/controllers/deployment/

• Scaling up / down easily number of replicas
• Rolling updates to deploy new SW version

Here's an example of a deployment for an NGINX app:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-deployment
  template:
    metadata:
      labels:
        app: my-deployment
    spec:
      containers:
      - name: nginx
        image: nginx:1.19.1
        ports:
        - containerPort: 80

Rolling Updates

https://kubernetes.io/docs/concepts/workloads/controllers/deployment/#updating-a-deployment

Three options for rolling updates:

1- Using imperative command kubectl set image: (use --record to easily rollback)

kubectl set image deployment/my-deployment nginx=nginx:1.19.2 --record

2- Using imperative command kubectl edit deploy:

kubectl edit deployment my-deployment

Note: any change is applied immediately, no need for kubectl apply

3- Editing specs in the deployment YAML manifest:

vi deployment.yaml
kubectl apply -f deployment.yaml

Check deployment status:

kubectl rollout status deployment my-deployment
kubectl rollout status deployment/my-deployment
kubectl rollout history deployment my-deployment

3.2 Understand deployments and how to perform rollbacks

https://kubernetes.io/docs/concepts/workloads/controllers/deployment/#rolling-back-a-deployment

Three options for rolling back:

1- Using imperative command kubectl rollout undo:

kubectl rollout history deployment/my-deployment
kubectl rollout undo deployment.v1.apps/my-deployment
kubectl rollout undo deployment.v1.apps/my-deployment --to-revision=1

Note: use --to-revision when —-record was used

2- Using imperative command kubectl edit deploy

kubectl edit deployment my-deployment
kubectl rollout status deployment my-deployment

Note: any change is applied immediately, no need for kubectl apply

3- Editing specs in the deployment YAML manifest:

vi deployment.yaml
kubectl apply -f deployment.yaml

Check rollout status:

kubectl rollout status deployment my-deployment
kubectl rollout history deployment my-deployment

3.3 Understand Jobs and CronJobs

Jobs

https://kubernetes.io/docs/concepts/workloads/controllers/job/

• A Job create 1 or more Pods to run tasks to completion
• Jobs track successful completion of tasks

Here's an example of a Job to clean up the content of /data directory on worker nodes:

apiVersion: batch/v1
kind: Job
metadata:
  name: cleanup
spec:
  template:
    spec:
      containers:
      - name: cleanup
        image: busybox
        command: ["/bin/sh",  "-c", "rm -rf /data/*"]
        volumeMounts:
        - mountPath: /data
          name: data
      restartPolicy: Never
  backoffLimit: 4
  volumes:
  - name: data
    hostPath:
      path: /data

Cronjobs

https://kubernetes.io/docs/concepts/workloads/controllers/cron-jobs/

• CronJob createa Jobs on a repeating schedule.
• runs a job periodically on a given schedule, written in Cron format.

Cron schedule syntax

# ┌───────────── minute (0 - 59)
# │ ┌───────────── hour (0 - 23)
# │ │ ┌───────────── day of the month (1 - 31)
# │ │ │ ┌───────────── month (1 - 12)
# │ │ │ │ ┌───────────── day of the week (0 - 6) (Sunday to Saturday;
# │ │ │ │ │                                   7 is also Sunday on some systems)
# │ │ │ │ │
# │ │ │ │ │
# * * * * *

Entry	Description	Equivalent to
@yearly (or @annually)	Run once a year at midnight of 1 January	0 0 1 1 *
@monthly	Run once a month at midnight of the first day of the month	0 0 1 * *
@weekly	Run once a week at midnight on Sunday morning	0 0 * * 0
@daily (or @midnight)	Run once a day at midnight	0 0 * * *
@hourly	Run once an hour at the beginning of the hour	0 * * * *

Sample Cronjob:

apiVersion: batch/v1beta1
kind: CronJob
metadata:
  name: hello
spec:
  schedule: "*/1 * * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: hello
            image: busybox
            imagePullPolicy: IfNotPresent
            command:
            - /bin/sh
            - -c
            - date; echo Hello from the Kubernetes cluster
          restartPolicy: OnFailure

3.4 Understand how to use Labels, Selectors, and Annotations

Labels

https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/

Here is a pod with some labels.

apiVersion: v1
kind: Pod
metadata:
  name: pod-with-label
  labels:
    app: my-app
    environment: production
spec:
  containers:
  - name: nginx
    image: nginx

You can view existing labels with kubectl describe.

Here is another pod with different labels.

kubectl describe pod my-production-label-pod

You can use various selectors to select different subsets of objects.

kubectl get pods -l app=my-app
kubectl get pods -l environment=production
kubectl get pods -l environment=development
kubectl get pods -l environment!=production
kubectl get pods -l 'environment in (development,production)'
kubectl get pods -l app=my-app,environment=production

Annotations

https://kubernetes.io/docs/concepts/overview/working-with-objects/annotations/

Here is a simple pod with some annotations.

apiVersion: v1
kind: Pod
metadata:
  name: pod-with-annotation
annotations:
  owner: joe@example.com
  git-commit: bdab0c6 
spec:
  containers:
  - name: nginx
  image: nginx

Like labels, existing annotations can also be viewed using kubectl describe.

kubectl describe pod my-annotation-pod