Updating ConfigMaps and propagation in Kubernetes - Mini Project: Build & Apply

Updating ConfigMaps and Propagation in Kubernetes

📖 Scenario: You are managing a Kubernetes cluster for a small web application. The application uses a ConfigMap to store configuration settings like the welcome message. You need to update the ConfigMap and see how the changes propagate to the running pods.

🎯 Goal: Learn how to create a ConfigMap, update it, and verify that the changes propagate to pods using volume mounts.

📋 What You'll Learn

Create a ConfigMap with a key-value pair

Create a pod that uses the ConfigMap as a volume

Update the ConfigMap with a new value

Verify the updated value inside the pod

💡 Why This Matters

🌍 Real World

ConfigMaps are used in Kubernetes to separate configuration from container images. Updating ConfigMaps and understanding how changes propagate helps keep applications flexible and easy to manage.

💼 Career

DevOps engineers and Kubernetes administrators frequently update ConfigMaps to change application behavior without rebuilding images. Knowing how to update and verify ConfigMaps is essential for managing live applications.

1

Create a ConfigMap with initial data

Create a ConfigMap named app-config with a key welcome_message and value Hello, Kubernetes! using the kubectl create configmap command.

Kubernetes

# Your code here

Need a hint?

Use kubectl create configmap app-config --from-literal=welcome_message='Hello, Kubernetes!' to create the ConfigMap.

2

Create a pod that uses the ConfigMap as a volume

Create a pod named configmap-pod using the busybox image. Mount the app-config ConfigMap as a volume at /etc/config. Use the command sleep 3600 to keep the pod running.

Kubernetes

kubectl create configmap app-config --from-literal=welcome_message='Hello, Kubernetes!'
# Your code here

Need a hint?

Use kubectl run to create the pod and patch it to add the ConfigMap volume and mount.

3

Update the ConfigMap with a new welcome message

Update the app-config ConfigMap to change the welcome_message value to Welcome to Kubernetes! using the kubectl create configmap --from-literal --dry-run=client -o yaml | kubectl apply -f - pattern.

Kubernetes

kubectl create configmap app-config --from-literal=welcome_message='Hello, Kubernetes!'
kubectl run configmap-pod --image=busybox --restart=Never -- sleep 3600
kubectl patch pod configmap-pod -p '{"spec":{"volumes":[{"name":"config-volume","configMap":{"name":"app-config"}}],"containers":[{"name":"configmap-pod","image":"busybox","command":["sleep","3600"],"volumeMounts":[{"name":"config-volume","mountPath":"/etc/config"}]}]}}' --type=merge
# Your code here

Need a hint?

Use kubectl create configmap app-config --from-literal=welcome_message='Welcome to Kubernetes!' --dry-run=client -o yaml | kubectl apply -f - to update the ConfigMap.

4

Verify the updated ConfigMap value inside the pod

Use kubectl exec to open a shell inside the configmap-pod pod and use cat /etc/config/welcome_message to display the updated welcome message.

Kubernetes

kubectl create configmap app-config --from-literal=welcome_message='Hello, Kubernetes!'
kubectl run configmap-pod --image=busybox --restart=Never -- sleep 3600
kubectl patch pod configmap-pod -p '{"spec":{"volumes":[{"name":"config-volume","configMap":{"name":"app-config"}}],"containers":[{"name":"configmap-pod","image":"busybox","command":["sleep","3600"],"volumeMounts":[{"name":"config-volume","mountPath":"/etc/config"}]}]}}' --type=merge
kubectl create configmap app-config --from-literal=welcome_message='Welcome to Kubernetes!' --dry-run=client -o yaml | kubectl apply -f -
# Your code here

Need a hint?

Use kubectl exec configmap-pod -- cat /etc/config/welcome_message to see the updated message inside the pod.