Scenario

Your application needs to react to configuration changes without requiring a pod restart.

Task

Create a ConfigMap and a pod with a sidecar that watches for configuration file changes. Mount the ConfigMap to both containers.

Sidecar container snippet is at /home/interview/watcher.yaml.

Step 1: Create the ConfigMap

kubectl create configmap app-config --from-literal=settings.conf="debug=false"

Step 2: Edit the watcher snippet to create full pod yaml

Edit to create complete pod spec:

apiVersion: v1                    # Add pod structure
kind: Pod
metadata:
  name: app-pod
spec:
  containers:
    - name: app                   # Add main container
      image: nginx:1.24
      volumeMounts:
        - name: config-volume
          mountPath: /etc/config
    - name: config-watcher
      image: busybox              # Fix: busybox888 -> busybox
      command:
        - sh
        - -c
        - |
          LAST_HASH=""
          while true; do
            CURRENT_HASH=$(cat /etc/config/settings.conf 2>/dev/null | md5sum)
            if [ "$CURRENT_HASH" != "$LAST_HASH" ] && [ -n "$LAST_HASH" ]; then
              echo "Config changed at $(date)"
              cat /etc/config/settings.conf
            fi
            LAST_HASH=$CURRENT_HASH
            sleep 5
          done
      volumeMounts:               # Add volumeMounts to sidecar
        - name: config-volume
          mountPath: /etc/config
  volumes:                        # Add volumes section
    - name: config-volume
      configMap:
        name: app-config

kubectl apply -f /home/interview/watcher.yaml

Step 3: Verify pod is running

kubectl get pod app-pod

Step 4: (Optional) Test by updating ConfigMap

kubectl edit configmap app-config
# Change debug=false to debug=true

The sidecar will detect the change:

kubectl logs app-pod -c config-watcher