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Exercise Set 01: Commands, Env, and Volumes

Exercise 1 — Command & Args Basics​

Create a Pod named echo-pod in the default namespace using the busybox image.

  • The container should print the message Hello from CKA every 5 seconds in an infinite loop.
  • Write the loop as a shell command using command and args fields (not baked into the image).
  • The pod should restart automatically if it exits.

Verify by checking the logs.

Exercise 2 — Args from Environment Variables​

Create a Pod named greeter using the busybox image.

  • Define an environment variable GREETING with the value Kubernetes is fun.
  • The container should run a shell command that prints the value of GREETING once and then exits.
  • Use args to pass the shell command; use command only to invoke the shell.

Exercise 3 — ConfigMap as Environment Variables + Volume​

Create a ConfigMap named app-config in the default namespace with the following data:

APP_ENV=production
LOG_LEVEL=debug

Then create a Pod named config-reader using the busybox image that does both of the following:

  • Injects APP_ENV and LOG_LEVEL as environment variables from the ConfigMap.
  • Mounts the entire ConfigMap as a volume at /etc/config.
  • On startup, runs a shell command that prints both env vars AND then cats every file under /etc/config.

Exercise 4 — Secret Mounted as Volume​

Create a Secret named db-creds with the following literal values:

username=admin
password=s3cr3t

Create a Pod named secret-reader using the busybox image that:

  • Mounts the secret as a volume at /etc/secrets.
  • Runs a command that reads and prints the contents of both username and password files from that path.
  • Does not use secretKeyRef env vars — only the volume mount.

Exercise 5 — Init Container Writing to a Shared Volume​

Create a Pod named init-writer with:

  • An init container using busybox that writes the text initialized at $(date) into a file at /work-dir/status.txt. Use command substitution in the shell command.
  • A main container using busybox that reads /work-dir/status.txt, prints it, then sleeps indefinitely.
  • Both containers share an emptyDir volume mounted at /work-dir.

Exercise 6 — Sidecar Sharing a Log Volume​

Create a Pod named log-app with two containers:

Container 1 — writer using busybox:

  • Every 3 seconds, appends a line like log entry: <number> (incrementing) to /var/log/app/out.log.
  • Uses a shell loop with a counter variable.

Container 2 — reader using busybox:

  • Runs tail -f /var/log/app/out.log.

Both containers share an emptyDir volume at /var/log/app.

Verify that kubectl logs log-app -c reader shows the entries being written by the writer.

Exercise 7 — Downward API as Environment Variables​

Create a Pod named downward-env using the busybox image that exposes the following as environment variables using the Downward API:

  • MY_POD_NAME → the pod's name
  • MY_POD_NAMESPACE → the pod's namespace
  • MY_NODE_NAME → the node the pod is scheduled on

The container should print all three values on startup and exit.

asciicast

Exercise 8 — Downward API as a Volume​

Create a Pod named downward-vol using the busybox image that:

  • Mounts pod metadata (specifically: name, namespace, and labels) as files under /etc/podinfo using a Downward API volume.
  • Add at least two labels to the pod (app=downward-vol, tier=backend).
  • On startup, cats all files under /etc/podinfo.

Exercise 9 — Combined: ConfigMap + Secret + Downward API + Shared Volume​

Create the following in the default namespace:

  • A ConfigMap pipeline-config with keys MODE=batch and TIMEOUT=30.
  • A Secret pipeline-secret with key API_KEY=abc123xyz.

Create a Pod named pipeline-runner with two containers:

Container 1 — setup (busybox, runs once then exits):

  • Has MODE and TIMEOUT injected as env vars from the ConfigMap.
  • Has API_KEY injected as an env var from the Secret.
  • Also exposes MY_POD_NAME via Downward API as an env var.
  • Writes a file /shared/config-dump.txt containing all four values (one per line, labeled).

Container 2 — runner (busybox):

  • Waits for /shared/config-dump.txt to exist (poll in a loop), then prints its contents and sleeps.

Both share an emptyDir at /shared.

Exercise 10 — Deployment with Configurable Replicas and Command Override​

Create a Deployment named worker in namespace tasks (create it if needed) with:

  • 3 replicas, image busybox.
  • A ConfigMap worker-config in the same namespace with key INTERVAL=10.
  • Each pod injects INTERVAL from the ConfigMap as an env var.
  • The container runs: sleep $INTERVAL in a loop, printing worker sleeping for $INTERVAL seconds before each sleep.
  • Set a restartPolicy that keeps the containers running.

Then, without deleting the deployment, update the INTERVAL value in the ConfigMap to 5 and confirm the behavior changes after the pods are restarted.