OOMKilled containers in Kubernetes - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to check pods that were OOMKilled.

Kubernetes

kubectl get pods --field-selector status.phase=Failed -o json | jq '.items[] | select(.status.containerStatuses[].state.terminated.reason == "[1]") | .metadata.name'

Drag options to blanks, or click blank then click option'

ACompleted

BCrashLoopBackOff

COOMKilled

DError

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'CrashLoopBackOff' instead of 'OOMKilled'.

Using 'Error' which is too generic.

The reason for containers killed due to out-of-memory is OOMKilled.

2fill in blank

medium

Complete the YAML snippet to set memory limit to 256Mi for a container.

Kubernetes

resources:
  limits:
    memory: [1]

Drag options to blanks, or click blank then click option'

A256MB

B256Mi

C256mb

D256M

Attempts:

3 left

💡 Hint

Common Mistakes

Using '256MB' which is invalid in Kubernetes YAML.

Using lowercase units like 'mb'.

In Kubernetes, memory limits use Mi (mebibytes) notation, so 256Mi is correct.

3fill in blank

hard

Fix the error in the command to describe a pod named 'webapp' in namespace 'prod'.

Kubernetes

kubectl describe pod [1] -n prod

Drag options to blanks, or click blank then click option'

Aprod

Bpod/webapp

C--webapp

Dwebapp

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prod' as pod name.

Using '--webapp' which is invalid flag.

The pod name is passed directly without prefix or flags. So just webapp is correct.

4fill in blank

hard

Fill both blanks to create a pod spec with memory request 128Mi and limit 256Mi.

Kubernetes

resources:
  requests:
    memory: [1]
  limits:
    memory: [2]

Drag options to blanks, or click blank then click option'

A128Mi

B256Mi

C512Mi

D64Mi

Attempts:

3 left

💡 Hint

Common Mistakes

Setting requests higher than limits.

Using invalid memory units.

Memory requests should be lower or equal to limits. Here, 128Mi request and 256Mi limit is correct.

5fill in blank

hard

Fill all three blanks to create a pod spec with container name 'app', memory request 100Mi, and limit 200Mi.

Kubernetes

containers:
- name: [1]
  resources:
    requests:
      memory: [2]
    limits:
      memory: [3]

Drag options to blanks, or click blank then click option'

Aapp

B100Mi

C200Mi

Dweb

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong container name.

Swapping request and limit values.

The container name is 'app', with memory request 100Mi and limit 200Mi as per spec.

Practice

1. What does it mean when a Kubernetes container status shows OOMKilled?

easy

A. The container was deleted manually by the user.

B. The container was restarted due to a network failure.

C. The container completed its task successfully.

D. The container was stopped because it used more memory than allowed.

Solution

1. Step 1: Understand OOMKilled meaning

   OOMKilled means Out Of Memory Killed, which happens when a container uses more memory than its limit.

2. Step 2: Relate to container status

   When a container exceeds its memory limit, Kubernetes stops it to protect the system.

3. Final Answer:

   The container was stopped because it used more memory than allowed. -> Option D

4. Quick Check:

   OOMKilled = Memory limit exceeded [OK]

Hint: OOMKilled means container used too much memory [OK]

Common Mistakes:

• Confusing OOMKilled with network errors
• Thinking OOMKilled means container finished normally
• Assuming OOMKilled is a manual stop

2. Which kubectl command helps you check why a pod's container was OOMKilled?

easy

A. kubectl get pods --all-namespaces

B. kubectl logs <pod-name>

C. kubectl describe pod <pod-name>

D. kubectl exec <pod-name> -- top

Solution

1. Step 1: Identify command to get pod details

   kubectl describe pod <pod-name> shows detailed pod info including container status and reasons for restarts.

2. Step 2: Confirm OOMKilled reason visibility

   This command shows events and container states, including if a container was OOMKilled.

3. Final Answer:

   kubectl describe pod <pod-name> -> Option C

4. Quick Check:

   Describe pod shows OOMKilled reason [OK]

Hint: Use 'kubectl describe pod' to see OOMKilled details [OK]

Common Mistakes:

• Using 'kubectl get pods' which lacks detailed reason
• Checking logs which may not show OOMKilled cause
• Running exec commands which don't show pod status

3. Given this pod description snippet, what caused the container to stop?

State: Terminated
Reason: OOMKilled
Exit Code: 137

medium

A. The container was killed because it used too much memory.

B. The container ran out of CPU resources.

C. The container was terminated due to a manual stop.

D. The container crashed due to a software error.

Solution

1. Step 1: Analyze the Reason field

   The Reason is 'OOMKilled', which means the container was killed because it exceeded memory limits.

2. Step 2: Understand Exit Code 137

   Exit code 137 means the process was killed by signal 9 (SIGKILL), typical for OOMKilled events.

3. Final Answer:

   The container was killed because it used too much memory. -> Option A

4. Quick Check:

   Reason OOMKilled + Exit 137 = Memory kill [OK]

Hint: Exit code 137 with OOMKilled means memory limit exceeded [OK]

Common Mistakes:

• Confusing CPU limits with memory limits
• Assuming manual stop without checking reason
• Thinking software error caused termination

4. You see a pod's container repeatedly OOMKilled. Which change fixes this issue?

medium

A. Increase the container's memory limit in the pod spec.

B. Decrease the container's CPU limit in the pod spec.

C. Remove the memory limit from the pod spec.

D. Restart the pod manually every time it OOMKills.

Solution

1. Step 1: Identify cause of repeated OOMKilled

   Repeated OOMKilled means the container needs more memory than allowed.

2. Step 2: Choose proper fix

   Increasing the memory limit lets the container use more memory and prevents OOMKilled.

3. Final Answer:

   Increase the container's memory limit in the pod spec. -> Option A

4. Quick Check:

   More memory limit stops OOMKilled [OK]

Hint: Raise memory limit to stop OOMKilled repeats [OK]

Common Mistakes:

• Lowering CPU limit which doesn't affect memory
• Removing memory limit causing instability
• Relying on manual restarts instead of fixing limits

5. A pod's container is OOMKilled even though its memory limit is set to 512Mi. You want to prevent this without increasing the limit. What is the best approach?

hard

A. Increase the CPU limit to speed up processing.

B. Optimize the application to use less memory inside the container.

C. Remove the memory limit to avoid OOMKilled.

D. Add more replicas of the pod to distribute load.

Solution

1. Step 1: Understand memory limit and OOMKilled

   The container hits the 512Mi limit and is killed. Increasing limit is not an option.

2. Step 2: Find alternative to increasing memory

   Optimizing the app to use less memory reduces usage below the limit, preventing OOMKilled.

3. Step 3: Evaluate other options

   Removing limit risks node stability, increasing CPU doesn't reduce memory, adding replicas doesn't fix memory per container.

4. Final Answer:

   Optimize the application to use less memory inside the container. -> Option B

5. Quick Check:

   Lower memory use avoids OOMKilled without raising limit [OK]

Hint: Reduce app memory use to avoid OOMKilled without raising limit [OK]

Common Mistakes:

• Removing memory limits causing node crashes
• Increasing CPU expecting memory fix
• Adding replicas without fixing memory use