Memory requests and limits in Kubernetes - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Memory Requests vs Limits

In Kubernetes, what happens if a container uses more memory than its memory request but less than its memory limit?

A The container is terminated immediately by the system.

B The container may be evicted depending on node pressure.

C The container is allowed to use the extra memory without any restrictions.

D The container's CPU usage is limited but memory usage is ignored.

💡 Hint

Think about how Kubernetes manages resources when the node is under memory pressure.

Memory requests define the guaranteed memory for a container. If usage goes above the request but below the limit, the container can continue running but may be evicted if the node runs low on memory.

💻 Command Output

intermediate

Check Memory Limits in a Pod

You run the command kubectl describe pod mypod. Which section shows the memory requests and limits for containers?

Kubernetes

kubectl describe pod mypod

A In the <strong>Volumes</strong> section describing storage.

B Under the <strong>Events</strong> section at the bottom of the output.

C In the <strong>Conditions</strong> section near the top.

D Under the <strong>Containers</strong> section, look for <code>Limits:</code> and <code>Requests:</code> lines.

💡 Hint

Memory settings are part of container resource specifications.

The kubectl describe pod command shows resource requests and limits under each container's details in the Containers section.

❓ Configuration

advanced

YAML for Memory Requests and Limits

Which YAML snippet correctly sets a memory request of 256Mi and a memory limit of 512Mi for a container?

A

resources:
  requests:
    memory: 256MB
  limits:
    memory: 512MB

B

resources:
  memory:
    request: 256Mi
    limit: 512Mi

C

resources:
  requests:
    memory: "256Mi"
  limits:
    memory: "512Mi"

D

resources:
  requests:
    memory: 256
  limits:
    memory: 512

💡 Hint

Check the correct indentation and units for memory in Kubernetes YAML.

Memory requests and limits must be under resources.requests.memory and resources.limits.memory with units like Mi (mebibytes).

❓ Troubleshoot

advanced

Pod Evicted Due to Memory Limit

A pod is repeatedly evicted with the message OOMKilled. What is the most likely cause?

A The pod's memory usage exceeded its memory limit.

B The pod's disk space was full.

C The pod's CPU usage exceeded its CPU request.

D The pod's network bandwidth was exceeded.

💡 Hint

OOMKilled means Out Of Memory killed by the system.

When a container uses more memory than its limit, the system kills it to protect the node.

✅ Best Practice

expert

Setting Memory Requests and Limits for Stability

Which practice helps ensure stable Kubernetes cluster performance regarding memory requests and limits?

A Set memory requests based on typical usage and limits slightly above peak usage to balance stability and flexibility.

B Set memory requests low and limits very high to allow containers to burst freely.

C Set memory requests equal to limits for all containers to avoid resource contention.

D Do not set memory requests or limits and let Kubernetes manage automatically.

💡 Hint

Think about balancing guaranteed resources and flexibility.

Setting requests based on typical usage ensures guaranteed resources, while limits above peak usage prevent excessive memory use and evictions.

Practice

1. What does the memory request specify in a Kubernetes pod configuration?

easy

A. The total memory available on the node

B. The maximum amount of memory the container can use

C. The amount of memory the container has currently used

D. The minimum amount of memory guaranteed for the container

Solution

1. Step 1: Understand memory request meaning

   Memory request is the minimum memory Kubernetes guarantees to a container so it can run without being killed due to lack of memory.

2. Step 2: Differentiate from memory limit

   Memory limit is the max memory allowed, not the minimum guaranteed.

3. Final Answer:

   The minimum amount of memory guaranteed for the container -> Option D

4. Quick Check:

   Memory request = minimum guaranteed memory [OK]

Hint: Requests = minimum guaranteed memory, limits = max allowed [OK]

Common Mistakes:

• Confusing memory request with memory limit
• Thinking request is the max memory
• Assuming request is current usage

2. Which of the following is the correct way to specify memory requests and limits in a Kubernetes pod YAML?

easy

A. resources:
requests:
memory: "256Mi"
limits:
memory: "512Mi"

B. resources:
memory:
request: 256
limit: 512

C. memory:
requests: 256Mi
limits: 512Mi

D. resources:
requests:
mem: 256Mi
limits:
mem: 512Mi

Solution

1. Step 1: Recall correct YAML structure for resources

   In Kubernetes, memory requests and limits are under resources.requests.memory and resources.limits.memory with values as strings including units like "Mi".

2. Step 2: Check each option for syntax correctness

   resources: requests: memory: "256Mi" limits: memory: "512Mi" matches the correct syntax. Options A, B, and C use wrong keys or structure.

3. Final Answer:

   resources: requests: memory: "256Mi" limits: memory: "512Mi" -> Option A

4. Quick Check:

   Correct YAML keys and units = resources: requests: memory: "256Mi" limits: memory: "512Mi" [OK]

Hint: Use resources.requests.memory and resources.limits.memory keys [OK]

Common Mistakes:

• Using wrong keys like 'mem' or 'memory' outside resources
• Omitting quotes or units for memory values
• Swapping 'request' and 'requests'

3. Given this pod spec snippet:

resources:
  requests:
    memory: "128Mi"
  limits:
    memory: "256Mi"

What happens if the container tries to use 300Mi of memory?

medium

A. The container is allowed to use 300Mi without issues

B. The container is throttled but not killed

C. The container is killed by Kubernetes for exceeding the memory limit

D. The container's memory usage is capped at 256Mi but continues running

Solution

1. Step 1: Understand memory limit enforcement

   Memory limit is the maximum memory a container can use. If it exceeds this, Kubernetes kills the container.

2. Step 2: Apply to given values

   The limit is 256Mi. Using 300Mi exceeds this limit, so the container will be terminated.

3. Final Answer:

   The container is killed by Kubernetes for exceeding the memory limit -> Option C

4. Quick Check:

   Memory usage > limit = container killed [OK]

Hint: Memory over limit kills container, not throttled [OK]

Common Mistakes:

• Thinking container is throttled instead of killed
• Confusing requests with limits
• Assuming container can burst beyond limit safely

4. You set memory requests to 512Mi and limits to 256Mi in your pod YAML. What is the problem?

medium

A. Memory limits cannot be lower than 256Mi

B. Memory requests cannot be higher than memory limits

C. This configuration is valid and will work fine

D. Requests and limits must be equal

Solution

1. Step 1: Recall relationship between requests and limits

   Memory requests must be less than or equal to memory limits. Requests are minimum guaranteed, limits are max allowed.

2. Step 2: Analyze given values

   Requests = 512Mi, Limits = 256Mi. Requests are higher than limits, which is invalid and causes an error.

3. Final Answer:

   Memory requests cannot be higher than memory limits -> Option B

4. Quick Check:

   Requests ≤ Limits rule violated [OK]

Hint: Requests must be ≤ limits, else config error [OK]

Common Mistakes:

• Setting requests higher than limits
• Assuming limits can be lower than requests
• Thinking requests and limits can be any values

5. You want to ensure your pod always has at least 200Mi memory but never uses more than 400Mi. How should you set memory requests and limits in the pod spec?

hard

A. requests.memory: "200Mi" and limits.memory: "400Mi"

B. requests.memory: "400Mi" and limits.memory: "200Mi"

C. requests.memory: "200Mi" only, no limits

D. limits.memory: "400Mi" only, no requests

Solution

1. Step 1: Identify minimum guaranteed memory

   Minimum memory guaranteed is set by requests.memory, so set it to 200Mi.

2. Step 2: Identify maximum allowed memory

   Maximum memory allowed is set by limits.memory, so set it to 400Mi.

3. Step 3: Verify correct order

   Requests must be ≤ limits, so 200Mi ≤ 400Mi is valid.

4. Final Answer:

   requests.memory: "200Mi" and limits.memory: "400Mi" -> Option A

5. Quick Check:

   Requests = 200Mi, Limits = 400Mi [OK]

Hint: Requests = min guaranteed, limits = max allowed [OK]

Common Mistakes:

• Swapping requests and limits values
• Setting only requests or only limits
• Setting requests higher than limits