Executing commands in Pods in Kubernetes - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of command executed inside a Pod

You run the command kubectl exec mypod -- ls /app on a Pod named mypod. The Pod's /app directory contains files index.html and config.yaml. What will be the output?

A

index.html
config.yaml

B

mypod
index.html
config.yaml

C Error: directory not found

D No resources found.

💡 Hint

The kubectl exec command runs the given command inside the Pod's container.

The ls /app command lists files inside the /app directory of the Pod. Since the directory contains index.html and config.yaml, these are listed.

🧠 Conceptual

intermediate

Understanding kubectl exec command syntax

Which of the following is the correct syntax to execute the command cat /etc/hosts inside a Pod named webserver?

A kubectl exec --webserver cat /etc/hosts

B kubectl exec webserver -- cat /etc/hosts

C kubectl exec webserver cat /etc/hosts

D kubectl exec -- pod=webserver -- cat /etc/hosts

💡 Hint

The Pod name comes immediately after kubectl exec, followed by -- to separate the command.

The correct syntax is kubectl exec POD_NAME -- COMMAND. Option B follows this format exactly.

❓ Troubleshoot

advanced

Troubleshooting kubectl exec permission error

You try to run kubectl exec mypod -- whoami but get the error: error: unable to upgrade connection: Forbidden. What is the most likely cause?

A The Kubernetes API server is down

B The Pod does not exist

C The command <code>whoami</code> is not installed in the Pod

D The user running kubectl lacks permission to exec into the Pod

💡 Hint

The error mentions 'Forbidden', which relates to permissions.

The 'Forbidden' error means the user does not have RBAC permissions to exec into the Pod. The Pod existing or command presence would cause different errors.

🔀 Workflow

advanced

Executing an interactive shell inside a Pod

You want to open an interactive bash shell inside a Pod named backend. Which command should you use?

A kubectl exec -it backend -- /bin/bash

B kubectl exec backend /bin/bash -i

C kubectl exec backend --interactive /bin/bash

D kubectl exec backend -bash -it

💡 Hint

Use flags -i and -t for interactive terminal.

The correct command uses -it flags before the Pod name and -- to separate the command. Option A is correct.

✅ Best Practice

expert

Best practice for running commands in multi-container Pods

A Pod has two containers: app and sidecar. You want to run ls /data inside the sidecar container. Which command is correct?

A kubectl exec mypod --container sidecar ls /data

B kubectl exec mypod --container sidecar -- ls /data

C kubectl exec mypod -c sidecar -- ls /data

D kubectl exec mypod --container=sidecar ls /data

💡 Hint

Use -c or --container with kubectl exec to specify container.

The correct syntax is kubectl exec POD -c CONTAINER -- COMMAND. Option C uses the short flag -c correctly. Options B and C have wrong flag usage or missing --. Option C misses -- separator.

Practice

1. What is the primary purpose of the kubectl exec command in Kubernetes?

easy

A. To list all Pods in a namespace

B. To create a new Pod

C. To run commands inside a running Pod

D. To delete a Pod

Solution

1. Step 1: Understand the function of kubectl exec

   The kubectl exec command is used to execute commands inside a running Pod's container.

2. Step 2: Differentiate from other commands

   Creating, deleting, or listing Pods are done with other commands like kubectl create, kubectl delete, and kubectl get.

3. Final Answer:

   To run commands inside a running Pod -> Option C

4. Quick Check:

   kubectl exec runs commands inside Pods [OK]

Hint: Remember: exec means execute inside Pod [OK]

Common Mistakes:

• Confusing exec with create or delete commands
• Thinking exec lists Pods
• Using exec to start new Pods

2. Which of the following is the correct syntax to run the command ls /app inside a Pod named web-pod?

easy

A. kubectl exec web-pod ls /app

B. kubectl exec web-pod -- ls /app

C. kubectl exec -- web-pod ls /app

D. kubectl exec -c web-pod ls /app

Solution

1. Step 1: Identify correct command separator

   The -- separates the Pod name from the command to run inside the Pod.

2. Step 2: Apply syntax rules

   The correct syntax is kubectl exec [pod-name] -- [command], so kubectl exec web-pod -- ls /app is correct.

3. Final Answer:

   kubectl exec web-pod -- ls /app -> Option B

4. Quick Check:

   Use -- before command [OK]

Hint: Use double dash (--) before command [OK]

Common Mistakes:

• Omitting the -- separator
• Placing -- before Pod name
• Using -c without container name

3. Given a Pod named db-pod with two containers: mysql and backup, what is the output of this command?

kubectl exec db-pod -c backup -- echo Hello

medium

A. Pod not found

B. Error: container name required

C. No such container: backup

D. Hello

Solution

1. Step 1: Understand the command components

   The command runs echo Hello inside the backup container of the db-pod Pod.

2. Step 2: Predict the command output

   Since the container exists and the command is valid, it outputs Hello.

3. Final Answer:

   Hello -> Option D

4. Quick Check:

   Correct container specified with -c outputs command result [OK]

Hint: Use -c to specify container, output is command result [OK]

Common Mistakes:

• Not specifying container when multiple exist
• Using wrong container name
• Expecting Pod name as container

4. You run this command but get an error:

kubectl exec mypod ls /data

What is the most likely cause?

medium

A. Missing -- before the command

B. Pod mypod does not exist

C. The ls command is invalid

D. You need to specify the container with -c

Solution

1. Step 1: Check command syntax

   The command is missing the -- separator between Pod name and command.

2. Step 2: Understand effect of missing --

   Without --, kubectl treats ls as a Pod or option, causing an error.

3. Final Answer:

   Missing -- before the command -> Option A

4. Quick Check:

   Always use -- before command [OK]

Hint: Always put -- before command to avoid errors [OK]

Common Mistakes:

• Forgetting the -- separator
• Assuming container must be specified when only one exists
• Thinking command is invalid

5. You want to run cat /etc/config inside the app-container of Pod multi-pod which has three containers. Which command is correct?

hard

A. kubectl exec multi-pod -c app-container -- cat /etc/config

B. kubectl exec multi-pod cat /etc/config -c app-container

C. kubectl exec -c app-container multi-pod cat /etc/config

D. kubectl exec multi-pod -- -c app-container cat /etc/config

Solution

1. Step 1: Identify correct order of options

   The -c option specifying the container must come after the Pod name and before the -- separator.

2. Step 2: Confirm command separator usage

   The -- must separate the Pod/container specification from the command to run.

3. Step 3: Validate each option

   kubectl exec multi-pod -c app-container -- cat /etc/config correctly places -c app-container before -- and then the command cat /etc/config.

4. Final Answer:

   kubectl exec multi-pod -c app-container -- cat /etc/config -> Option A

5. Quick Check:

   -c before --, then command [OK]

Hint: Put -c before --, then command [OK]

Common Mistakes:

• Placing -c after the command
• Putting -- before -c
• Omitting -- separator