Kubernetes - ConfigMaps

Prerequisites

• Kubernetes
• kubectl

Assignment

• Lets start by creating a configmap to pass the environmental variables to the pod.

Job

1️⃣ Create a ConfigMap with two entries using the –from-literal parameter.

kubectl create configmap colour-configmap --from-literal=COLOUR=red --from-literal=KEY=value

kubectl describe configmap/colour-configmap

kubectl delete configmap/colour-configmap

2️⃣ Use an alternative approach for creating the same ConfigMap.

cat <<EOF > configmap-colour.properties
COLOUR=green
KEY=value
EOF

cat configmap-colour.properties

kubectl create configmap colour-configmap --from-env-file=configmap-colour.properties

kubectl describe configmap/colour-configmap

3️⃣ Create a pod that dumps environmental variables and sleeps for infinity. Review the environmental variables dumped by the pod.

kubectl run --image=ubuntu --dry-run=client --restart=Never -o yaml ubuntu --command bash -- -c 'env; sleep infinity' | tee env-dump-pod.yaml

kubectl apply -f env-dump-pod.yaml

kubectl get pods

kubectl logs ubuntu

4️⃣ Update the pod definition to include the configmap using envFrom.

cat <<EOF > env-dump-pod.yaml
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: ubuntu
  name: ubuntu
spec:
  containers:
  - command:
    - bash
    - -c
    - env; sleep infinity
    image: ubuntu
    name: ubuntu
    resources: {}
    envFrom:
    - configMapRef:
        name: colour-configmap
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}
EOF

cat <<EOF > calculatepi.yaml
apiVersion: batch/v1
kind: Job
metadata:
  creationTimestamp: null
  name: calculatepi
spec:
  completions: 20
  parallelism: 5
  template:
    metadata:
      creationTimestamp: null
    spec:
      containers:
      - command:
        - perl
        - -Mbignum=bpi
        - -wle
        - print bpi(2000)
        image: perl:5.34.0
        name: calculatepi
        resources: {}
      restartPolicy: Never
status: {}
EOF

kubectl apply -f env-dump-pod.yaml

5️⃣ The above command will fail as we can only update certain fields of a pod. Recreate the pod with the configmap.

kubectl delete -f env-dump-pod.yaml --now; kubectl apply -f env-dump-pod.yaml

kubectl logs ubuntu

6️⃣ Edit the configmap and change the color to red. Recreate the pod and verify the changes.

kubectl edit configmap/colour-configmap

kubectl delete -f env-dump-pod.yaml --now && kubectl apply -f env-dump-pod.yaml

kubectl logs ubuntu

7️⃣ Make the configmap immutable and update the color to purple. Try changing the color to yellow and confirm that if fails are configmap is immutable.

kubectl edit configmap/colour-configmap

kubectl delete -f env-dump-pod.yaml --now && kubectl apply -f env-dump-pod.yaml

kubectl logs ubuntu

8️⃣ Delete the pod and configmaps.

kubectl delete pod/ubuntu configmap/colour-configmap --now

rm configmap-colour.properties env-dump-pod.yaml