CPU requests and limits in Kubernetes - Mini Project: Build & Apply

CPU Requests and Limits in Kubernetes

📖 Scenario: You are managing a Kubernetes cluster for a small web application. To ensure the application runs smoothly without using too many resources, you need to set CPU requests and limits for the application pod.

🎯 Goal: Learn how to define CPU requests and limits in a Kubernetes pod configuration to control resource usage effectively.

📋 What You'll Learn

Create a pod configuration with a container named webapp

Set the CPU request to 250m (250 millicores)

Set the CPU limit to 500m (500 millicores)

Use the correct YAML structure for resource requests and limits

💡 Why This Matters

🌍 Real World

Setting CPU requests and limits is essential in Kubernetes to ensure applications get enough resources without overloading the cluster.

💼 Career

Understanding resource management in Kubernetes is a key skill for DevOps engineers and cloud administrators.

1

Create the basic pod YAML skeleton

Create a YAML file with a pod named cpu-demo-pod and a container named webapp using the image nginx. Include the required fields: apiVersion, kind, metadata, and spec with the container definition.

Kubernetes

apiVersion: v1
kind: Pod
metadata:
  name: cpu-demo-pod
spec:
  containers:
  - name: webapp
    image: nginx
    # Your code here

Hint

Start with the basic pod structure and container details.

2

Add CPU requests to the container

Add a resources section under the webapp container. Inside resources, add requests with cpu: "250m" to request 250 millicores of CPU.

Kubernetes

apiVersion: v1
kind: Pod
metadata:
  name: cpu-demo-pod
spec:
  containers:
  - name: webapp
    image: nginx
    # Add CPU requests here

Hint

Indent resources under the container, then add requests with the CPU value.

3

Add CPU limits to the container

Extend the resources section by adding limits with cpu: "500m" to limit CPU usage to 500 millicores.

Kubernetes

apiVersion: v1
kind: Pod
metadata:
  name: cpu-demo-pod
spec:
  containers:
  - name: webapp
    image: nginx
    resources:
      requests:
        cpu: "250m"
      # Add CPU limits here

Hint

Under resources, add limits with the CPU limit value.

4

Display the final pod YAML

Print the complete YAML configuration for the pod named cpu-demo-pod with the container webapp that has CPU requests and limits set.

Kubernetes

# Print the YAML configuration
# Your code here

Hint

Show the full YAML text as the output.

Practice

1. What does setting a cpu request in a Kubernetes pod specification do?

easy

A. It guarantees a minimum amount of CPU for the container.

B. It limits the maximum CPU the container can use.

C. It sets the CPU priority for the container.

D. It reserves memory for the container.

Solution

1. Step 1: Understand CPU request meaning

   CPU request is the minimum CPU resource Kubernetes guarantees to a container.

2. Step 2: Differentiate from CPU limit

   CPU limit sets the maximum CPU usage, not the minimum guaranteed.

3. Final Answer:

   It guarantees a minimum amount of CPU for the container. -> Option A

4. Quick Check:

   CPU request = minimum CPU guaranteed [OK]

Hint: Requests guarantee minimum CPU, limits cap maximum CPU [OK]

Common Mistakes:

• Confusing CPU request with CPU limit
• Thinking requests set maximum CPU
• Mixing CPU with memory resource

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

easy

A. resources:
cpu:
request: 500m
limit: 1

B. resources:
requests:
cpu: 500
limits:
cpu: 1000

C. resources:
requests:
cpu: "500m"
limits:
cpu: "1"

D. resources:
requests:
cpu: "1.0"
limits:
cpu: "0.5"

Solution

1. Step 1: Check correct YAML structure for resources

   The correct keys are requests and limits under resources, with CPU values as strings with units like "500m" or "1".

2. Step 2: Validate resources: requests: cpu: "500m" limits: cpu: "1" format

   resources: requests: cpu: "500m" limits: cpu: "1" uses correct keys and units: "500m" means 0.5 CPU, "1" means 1 CPU core.

3. Final Answer:

   resources: requests: cpu: "500m" limits: cpu: "1" -> Option C

4. Quick Check:

   Correct YAML keys and CPU units = resources: requests: cpu: "500m" limits: cpu: "1" [OK]

Hint: Use 'requests' and 'limits' keys with CPU as string with units [OK]

Common Mistakes:

• Using 'request' instead of 'requests'
• Specifying CPU as numbers without quotes or units
• Mixing up 'cpu' and 'memory' keys

3. Given this pod spec snippet:

resources:
  requests:
    cpu: "200m"
  limits:
    cpu: "500m"

What happens if the container tries to use 600m CPU?

medium

A. The container will be killed immediately.

B. The container will be throttled to 500m CPU.

C. The container will be allowed to use 600m CPU.

D. The container will be throttled to 200m CPU.

Solution

1. Step 1: Understand CPU limit effect

   The CPU limit is the maximum CPU the container can use. Here it is 500m (0.5 CPU).

2. Step 2: Predict container behavior when exceeding limit

   If the container tries to use 600m CPU, Kubernetes throttles it to the limit, 500m CPU.

3. Final Answer:

   The container will be throttled to 500m CPU. -> Option B

4. Quick Check:

   CPU limit caps usage = throttled to 500m [OK]

Hint: CPU usage above limit gets throttled to limit [OK]

Common Mistakes:

• Thinking container can exceed CPU limit
• Confusing throttling with killing container
• Assuming CPU request is the max limit

4. You wrote this pod spec:

resources:
  requests:
    cpu: "100m"
  limits:
    cpu: "50m"

What is wrong with this configuration?

medium

A. CPU requests and limits cannot be set together.

B. CPU request is less than CPU limit, which is invalid.

C. CPU values must be integers, not strings.

D. CPU limit is less than CPU request, which is invalid.

Solution

1. Step 1: Compare CPU request and limit values

   CPU request is 100m (0.1 CPU), CPU limit is 50m (0.05 CPU).

2. Step 2: Validate Kubernetes rules for requests and limits

   CPU limit must be equal or greater than CPU request. Here limit < request, which is invalid.

3. Final Answer:

   CPU limit is less than CPU request, which is invalid. -> Option D

4. Quick Check:

   Limit >= Request rule violated = CPU limit is less than CPU request, which is invalid. [OK]

Hint: Limit must be >= request, else config is invalid [OK]

Common Mistakes:

• Setting limit less than request
• Thinking CPU values must be integers
• Believing requests and limits can't coexist

5. You want to ensure a container always gets at least 250m CPU but never uses more than 750m CPU. Which YAML snippet correctly sets this with CPU requests and limits?

hard

A. resources:
requests:
cpu: "250m"
limits:
cpu: "750m"

B. resources:
requests:
cpu: "750m"
limits:
cpu: "250m"

C. resources:
requests:
cpu: 0.25
limits:
cpu: 0.75

D. resources:
requests:
cpu: "0.75"
limits:
cpu: "0.25"

Solution

1. Step 1: Identify correct CPU units and values

   CPU values can be specified as millicores with 'm' suffix, e.g., "250m" for 0.25 CPU.

2. Step 2: Check request and limit order

   Request must be less than or equal to limit. resources: requests: cpu: "250m" limits: cpu: "750m" sets request to 250m and limit to 750m correctly.

3. Final Answer:

   resources: requests: cpu: "250m" limits: cpu: "750m" -> Option A

4. Quick Check:

   Request 250m ≤ Limit 750m with correct units = resources: requests: cpu: "250m" limits: cpu: "750m" [OK]

Hint: Use millicores with 'm' and keep request ≤ limit [OK]

Common Mistakes:

• Swapping request and limit values
• Using decimal numbers without quotes
• Not using millicores for fractional CPU