Executing commands in Pods in Kubernetes - Mini Project: Build & Apply

Executing Commands in Kubernetes Pods

📖 Scenario: You are managing a Kubernetes cluster. Sometimes you need to run commands inside a running Pod to check its status or debug issues.

🎯 Goal: Learn how to execute commands inside a Kubernetes Pod using kubectl exec.

📋 What You'll Learn

Create a Pod manifest with a specific name and image

Add a label to the Pod for easy selection

Use kubectl exec to run a command inside the Pod

Display the output of the command executed inside the Pod

💡 Why This Matters

🌍 Real World

Running commands inside Pods helps troubleshoot and inspect running applications without needing to redeploy or restart them.

💼 Career

Kubernetes administrators and DevOps engineers often use <code>kubectl exec</code> to debug issues and verify application states inside containers.

1

Create a Pod manifest

Create a YAML file named mypod.yaml that defines a Pod with the name mypod using the image busybox. The Pod should run the command sleep 3600 to keep it alive.

Kubernetes

# Create a YAML manifest for the Pod named mypod
# Your code here

Hint

Use apiVersion: v1, kind: Pod, and specify metadata.name as mypod. Under spec.containers, set the container name, image, and command.

2

Add a label to the Pod

Add a label app: testpod under metadata.labels in the mypod.yaml file.

Kubernetes

apiVersion: v1
kind: Pod
metadata:
  name: mypod
  # Add labels here
  labels:
    app: testpod
spec:
  containers:
  - name: busybox-container
    image: busybox
    command: ["sleep", "3600"]
# Your code here

Hint

Under metadata, add a labels section with app: testpod.

3

Execute a command inside the Pod

Use the command kubectl exec mypod -- ls / to list the root directory inside the Pod.

Kubernetes

# Run the command to list root directory inside the Pod
# Your code here

Hint

Use kubectl exec followed by the Pod name mypod, then -- and the command ls /.

4

Display the output of the command

Run the command kubectl exec mypod -- ls / in your terminal and write the output exactly as it appears.

Kubernetes

# Paste the output of the command here
# Your output here

Hint

Run the command in your terminal and copy the exact output listing the root directories inside the Pod.

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