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Sample CKAD Application Design and Build Q&A

Application Design and Build – 20%

  • Define, build and modify container images **
  • Understand Jobs and CronJobs
  • Understand multi-container Pod design patterns (e.g. sidecar, init and others)
  • Utilize persistent and ephemeral volumes **

01-01. Docker Question

  • Create a container from the attached Dockerfile and index.html.
  • Name the image my-image.
  • Run the container exposing port 8080 on the host and port 80 on the container.
  • Name the container my-container. Stop the container. Delete the container.
Docker Image Creation

Create a file called index.html

mkdir -p ~/ckad/
vi ~/ckad/index.html

Edit index.html with the following text.

Hardships often prepare ordinary people for an extraordinary destiny.

Create a file called Dockerfile

vi ~/ckad/Dockerfile

Edit the Docker with to include the text below :

FROM nginx:latest
COPY ./index.html /usr/share/nginx/html/index.html
cd ~/ckad/
clear
# Build the docker image
docker build -t my-image:v0.1 .
docker images
# Create a TAR file from the image file
docker save --output my-image.tar my-image:v0.1
ls my-image*

Docker Container Operations

kubernetes.io bookmark: docker run

clear
# Run the docker image
docker run -it --rm -d -p 8080:80 --name my-container my-image:v0.1
clear
# Verify Operation
curl localhost:8080
clear
# List all images
docker ps -a
clear
# Stop the Container
docker container stop my-container
clear
# Delete the Image
docker image rm my-image:v0.1

Docker Operations 

clear
# Prune all dangling images
docker image prune -a


01-02. Name Container Question

  • Create a namespace called pod-namespace.
  • Create a pod called pod-1 using nginx image.
  • The container in the pod should be named container-1.
Prerequisites 

clear
# Create the namespace
kubectl create namespace pod-namespace
clear
# Switch context into the namespace so that all subsequent commands execute inside that namespace.
kubectl config set-context --current --namespace=pod-namespace
Help Examples
clear
# Run the help flag to get examples
kubectl run -h | more

Output:

Examples:

# Start a nginx pod

kubectl run nginx --image=nginx

# Start a hazelcast pod and let the container expose port 5701

kubectl run hazelcast --image=hazelcast/hazelcast --port=5701

# Start a hazelcast pod and set environment variables "DNS_DOMAIN=cluster" and "POD_NAMESPACE=default" in the

container
kubectl run hazelcast --image=hazelcast/hazelcast --env="DNS_DOMAIN=cluster" --env="POD_NAMESPACE=default"

# Start a hazelcast pod and set labels "app=hazelcast" and "env=prod" in the container

kubectl run hazelcast --image=hazelcast/hazelcast --labels="app=hazelcast,env=prod"

# Dry run; print the corresponding API objects without creating them

kubectl run nginx --image=nginx --dry-run=client 👈👈👈 This example matches most closely to the question. Just needs an output file.

# Start a nginx pod, but overload the spec with a partial set of values parsed from JSON

kubectl run nginx --image=nginx --overrides='{ "apiVersion": "v1", "spec": { ... } }'

# Start a busybox pod and keep it in the foreground, don't restart it if it exits

kubectl run -i -t busybox --image=busybox --restart=Never

# Start the nginx pod using the default command, but use custom arguments (arg1 .. argN) for that command

kubectl run nginx --image=nginx -- <arg1> <arg2> ... <argN>

# Start the nginx pod using a different command and custom arguments

kubectl run nginx --image=nginx --command -- <cmd> <arg1> ... <argN>

Solution

kubernetes.io bookmark: kubectl Cheat Sheet

clear
# Using the best example that matches the question
mkdir -p ~/ckad/
kubectl run pod-1 --image=nginx --dry-run=client -o yaml > ~/ckad/01-02.yml
clear
# Edit the YAML file to make required changes
# Use the Question number in case you want to return to the question for reference or for review
vi ~/ckad/01-02.yml
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: pod-1
  name: pod-1
spec:
  containers:
  - image: nginx
    name: container-1 #👈👈👈 Change from pod-1 to container-1
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}
clear
# Apply the YAML file to the Kubernetes API server
kubectl apply -f ~/ckad/01-02.yml
clear
# Quick verification that the pod was created and is working
kubectl get pod --watch


01-03. Storage Question

  • Create a namespace called storage-namespace.
  • Create a Persistent Volume called my-pv with 5Gi storage using hostPath /mnt/my-host.
  • Create a Persistent Volume Claim called my-pvc with 2Gi storage.
  • Create a pod called storage-pod using the nginx image.
  • Mount the Persistent Volume Claim onto /my-mount in storage-pod.
Overview

06-pv-pvc-pod

Legend

  • PersistentVolume – the low level representation of a storage volume
  • PersistentVolumeClaim – the binding between a Pod and PersistentVolume
  • Pod – a running container that will consume a PersistentVolume
  • StorageClass – allows for dynamic provisioning of PersistentVolumes

Access Modes

  • ReadWriteOnce(RWO) - volume can be mounted as read-write by a single node.
  • ReadOnlyMany(ROX) - volume can be mounted read-only by many nodes.
  • ReadWriteMany(RWX) - volume can be mounted as read-write by many nodes.
  • ReadWriteOncePod(RWOP) - volume can be mounted as read-write by a single Pod.

Notes

  • Once a PV is bound to a PVC, that PV is essentially tied to the PVC and cannot be bound to by another PVC.
  • There is a one-to-one mapping of PVs and PVCs.
  • However, multiple pods in the same project can use the same PVC.
  • The link between PV and PVC is not explict, instead the PVC makes a some requests for storage.
  • Kubernetes will pick an appropriate PersistentVolume to meet that claim.
  • StorageClass provisions PV dynamically, when PVC claims it.
  • StorageClass allows for dynamically provisioned volumes for an incoming claim.

Prerequisites 

clear
kubectl create namespace storage-namespace
kubectl config set-context --current --namespace=storage-namespace

Solution - PersistentVolume

kubernetes.io bookmark: Create a PersistentVolume

# Create a YAML file for the PV
mkdir -p ~/ckad/
vi ~/ckad/01-03-pv.yml
apiVersion: v1
kind: PersistentVolume
metadata:
  name: my-pv #👈👈👈 Change
  labels:
    type: local
spec:
  storageClassName: manual
  capacity:
    storage: 5Gi #👈👈👈 Change
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: "/mnt/my-host" #👈👈👈 Change
kubectl apply -f ~/ckad/01-03-pv.yml
clear
kubectl get pv

Output:

# Note the STATUS=Available
NAME      CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM
my-pv     5Gi        RWO            Retain           Available

Solution - PersistentVolumeClaim

kubernetes.io bookmark: Create a PersistentVolumeClaim

# Create a YAML file for the PVC
mkdir -p ~/ckad/
vi ~/ckad/01-03-pvc.yml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-pvc #👈👈👈 Change
spec:
  storageClassName: manual
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 2Gi #👈👈👈 Change
kubectl apply -f ~/ckad/01-03-pvc.yml
clear
kubectl get pv
kubectl get pvc

Output:

NAME      CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM
my-pv     5Gi        RWO            Retain           Bound       storage-namespace/my-pvc  # STATUS=Bound means the PV and PVC are linked

NAME     STATUS   VOLUME   CAPACITY   ACCESS MODES   STORAGECLASS   AGE
my-pvc   Bound    my-pv    5Gi        RWO            manual         6s                     # STATUS=Bound means the PV and PVC are linked

Solution - Pod

kubernetes.io bookmark: Create a Pod

# Create a YAML file for the Pod
mkdir -p ~/ckad/
vi  ~/ckad/01-03-pod.yml
apiVersion: v1
kind: Pod
metadata:
  name: storage-pod #👈👈👈 Change
spec:
  volumes:
    - name: my-volume
      persistentVolumeClaim:
        claimName: my-pvc #👈👈👈 Change
  containers:
    - name: my-container
      image: nginx
      ports:
        - containerPort: 80
          name: "http-server"
      volumeMounts:
        - mountPath: "/my-mount" #👈👈👈 Change
          name: my-volume

kubectl apply -f ~/ckad/01-03-pod.yml
clear
# Verify that the volume is mounted
# Or just kubectl describe pod storage-pod
kubectl describe pod storage-pod | grep -i Mounts -A1

Output:

    Mounts:
      /my-mount from my-volume (rw)    # Success


Clean Up

Clean Up 

cd
yes | rm -R ~/ckad/
kubectl delete ns storage-namespace --force
kubectl delete ns pod-namespace --force
kubectl delete pv my-pv

End of Section