Memory requests and limits in Kubernetes - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a memory request in Kubernetes?

A memory request is the amount of memory a container is guaranteed to have. Kubernetes uses this to decide which node can run the container.

beginner

What happens if a container exceeds its memory limit in Kubernetes?

If a container uses more memory than its limit, Kubernetes may terminate the container to protect the node's stability.

intermediate

Why should you set both memory requests and limits?

Setting both helps Kubernetes schedule containers efficiently and prevents any container from using too much memory and affecting others.

intermediate

How does Kubernetes use memory requests during scheduling?

Kubernetes checks if a node has enough free memory to meet the container's memory request before placing it there.

beginner

What is the difference between memory request and memory limit?

Memory request is the minimum memory guaranteed to a container. Memory limit is the maximum memory the container can use before being terminated.

What does the memory request specify in a Kubernetes pod?

A The minimum memory guaranteed to the container

B The maximum memory the container can use

C The total memory of the node

D The CPU usage limit

Memory request is the minimum memory Kubernetes guarantees to the container.

What happens if a container exceeds its memory limit?

A The container is terminated by Kubernetes

B The container is given more memory automatically

C Nothing happens, it continues running

D The node shuts down

Kubernetes kills containers that use more memory than their limit to keep the system stable.

Why is it important to set memory requests?

A To increase network bandwidth

B To limit CPU usage

C To help Kubernetes schedule pods on nodes with enough memory

D To set disk space limits

Memory requests help Kubernetes decide where to place pods based on available memory.

If a pod has a memory request of 500Mi and a limit of 1Gi, what does this mean?

A The pod can only use 500Mi memory

B The pod is guaranteed 500Mi memory and can use up to 1Gi

C The pod must use exactly 1Gi memory

D The pod has no memory limits

The request is the guaranteed memory, and the limit is the maximum allowed.

What is the risk of not setting memory limits?

A The container will use less memory

B The container will not start

C The pod will be scheduled on the wrong node

D A container might use too much memory and crash the node

Without limits, a container can consume excessive memory and affect node stability.

Explain how memory requests and limits work together in Kubernetes to manage container memory.

Think about how Kubernetes decides where to place containers and what happens if they use too much memory.

Describe why setting memory requests and limits is important for a stable Kubernetes cluster.

Consider what happens if one container uses too much memory without limits.

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