Limit ranges for defaults in Kubernetes - Mini Project: Build & Apply

Limit Ranges for Defaults in Kubernetes

📖 Scenario: You are managing a Kubernetes cluster where developers deploy their applications. To ensure fair resource usage and avoid accidental overconsumption, you want to set default resource limits and requests for all pods in a namespace.

🎯 Goal: Create a Kubernetes LimitRange resource that sets default CPU and memory requests and limits for containers in a namespace.

📋 What You'll Learn

Create a LimitRange YAML manifest named limitrange.yaml

Set default CPU request to 100m and default memory request to 200Mi

Set default CPU limit to 500m and default memory limit to 500Mi

Apply the LimitRange to the development namespace

💡 Why This Matters

🌍 Real World

In real Kubernetes clusters, setting default resource limits helps avoid resource starvation and ensures fair sharing among applications.

💼 Career

DevOps engineers and cluster administrators use LimitRanges to enforce resource policies and maintain cluster stability.

1

Create the basic LimitRange YAML skeleton

Create a YAML file named limitrange.yaml with the following top-level keys: apiVersion set to v1, kind set to LimitRange, and metadata with name set to resource-limits and namespace set to development.

Kubernetes

apiVersion: v1
kind: LimitRange
metadata:
  name: resource-limits
  namespace: development
# Your code here

Hint

Use the apiVersion, kind, and metadata fields to define the LimitRange resource.

2

Add the spec and limits section

Add a spec section with a limits list containing one item. This item should have type set to Container.

Kubernetes

apiVersion: v1
kind: LimitRange
metadata:
  name: resource-limits
  namespace: development
spec:
  limits:
  - type: Container
  # Your code here

Hint

The spec section defines the rules. The limits list holds the limit definitions.

3

Set default CPU and memory requests and limits

Inside the limits item, add defaultRequest with cpu: 100m and memory: 200Mi, and default with cpu: 500m and memory: 500Mi.

Kubernetes

apiVersion: v1
kind: LimitRange
metadata:
  name: resource-limits
  namespace: development
spec:
  limits:
  - type: Container
    # Your code here

Hint

Use defaultRequest for default resource requests and default for default limits.

4

Apply the LimitRange to the development namespace and verify

Run the command kubectl apply -f limitrange.yaml to create the LimitRange in the development namespace. Then run kubectl get limitrange resource-limits -n development -o yaml to display the applied LimitRange.

Kubernetes

apiVersion: v1
kind: LimitRange
metadata:
  name: resource-limits
  namespace: development
spec:
  limits:
  - type: Container
    defaultRequest:
      cpu: 100m
      memory: 200Mi
    default:
      cpu: 500m
      memory: 500Mi
# Your code here

Hint

Use kubectl apply -f limitrange.yaml to apply and kubectl get limitrange resource-limits -n development -o yaml to verify.

Practice

1. What is the main purpose of a LimitRange in a Kubernetes namespace?

easy

A. To schedule pods on specific nodes

B. To set default and maximum resource limits for containers in that namespace

C. To create network policies for pods

D. To manage persistent storage volumes

Solution

1. Step 1: Understand LimitRange role

   A LimitRange defines default, minimum, and maximum resource limits for containers in a namespace.

2. Step 2: Compare with other options

   Network policies, scheduling, and storage are managed by other Kubernetes resources, not LimitRange.

3. Final Answer:

   To set default and maximum resource limits for containers in that namespace -> Option B

4. Quick Check:

   LimitRange controls resource limits = C [OK]

Hint: LimitRange controls resource limits, not networking or storage [OK]

Common Mistakes:

• Confusing LimitRange with NetworkPolicy
• Thinking LimitRange schedules pods
• Assuming LimitRange manages storage

2. Which of the following is the correct YAML snippet to set a default CPU request of 100m using a LimitRange?

easy

A. apiVersion: v1\nkind: LimitRange\nmetadata:\n name: cpu-default\nspec:\n limits:\n - default:\n cpu: 100m\n type: Container

B. apiVersion: v1\nkind: LimitRange\nmetadata:\n name: cpu-default\nspec:\n limits:\n - defaultRequest:\n cpu: 100m\n type: Container

C. apiVersion: v1\nkind: LimitRange\nmetadata:\n name: cpu-default\nspec:\n limits:\n - defaultLimit:\n cpu: 100m\n type: Container

D. apiVersion: v1\nkind: LimitRange\nmetadata:\n name: cpu-default\nspec:\n limits:\n - defaultCpu:\n cpu: 100m\n type: Container

Solution

1. Step 1: Check LimitRange syntax for default

   The correct key to set default resource requests or limits is default under limits.

2. Step 2: Validate the YAML snippet

   apiVersion: v1\nkind: LimitRange\nmetadata:\n name: cpu-default\nspec:\n limits:\n - default:\n cpu: 100m\n type: Container uses default: with cpu: 100m correctly under limits and type: Container.

3. Final Answer:

   Option A is the correct YAML snippet -> Option A

4. Quick Check:

   Use default key for defaults in LimitRange [OK]

Hint: Use 'default' key under limits to set default resources [OK]

Common Mistakes:

• Using incorrect keys like defaultRequest or defaultLimit
• Misplacing keys outside limits array
• Wrong indentation in YAML

3. Given this LimitRange YAML applied in a namespace:

apiVersion: v1
kind: LimitRange
metadata:
  name: mem-default
spec:
  limits:
  - default:
      memory: 256Mi
    type: Container

What will be the memory request for a container without any memory request specified?

medium

A. No memory request will be set

B. Pod creation will fail due to missing memory request

C. Memory request will be unlimited

D. 256Mi memory request will be applied by default

Solution

1. Step 1: Understand default in LimitRange

   The default memory value sets the memory request if the container does not specify one.

2. Step 2: Apply to container without memory request

   Since the container has no memory request, Kubernetes applies the default 256Mi memory request from LimitRange.

3. Final Answer:

   256Mi memory request will be applied by default -> Option D

4. Quick Check:

   Default resource applies if container omits it [OK]

Hint: Default applies only if container omits resource request [OK]

Common Mistakes:

• Assuming no default means no request
• Thinking pod creation fails without explicit request
• Confusing default with max or min limits

4. You applied this LimitRange YAML:

apiVersion: v1
kind: LimitRange
metadata:
  name: cpu-limit
spec:
  limits:
  - max:
      cpu: 500m
    type: Container

Your pod container requests 600m CPU. What will happen?

medium

A. Pod will be created with 600m CPU request

B. Pod will ignore LimitRange and use 600m CPU

C. Pod creation will fail due to exceeding max CPU limit

D. Pod CPU request will be automatically reduced to 500m

Solution

1. Step 1: Understand max limit enforcement

   LimitRange max limits set the maximum allowed resource request or limit for containers.

2. Step 2: Check pod CPU request against max

   The pod requests 600m CPU, which exceeds the max 500m CPU set by LimitRange.

3. Step 3: Kubernetes behavior on violation

   Kubernetes rejects pod creation if resource requests exceed LimitRange max limits.

4. Final Answer:

   Pod creation will fail due to exceeding max CPU limit -> Option C

5. Quick Check:

   Exceeding max limit causes pod creation failure [OK]

Hint: Requests above max limit cause pod creation failure [OK]

Common Mistakes:

• Assuming Kubernetes auto-adjusts resource requests
• Thinking pod ignores LimitRange max limits
• Confusing max limit with default value

5. You want all containers in a namespace to have a default CPU request of 200m and a default memory request of 512Mi, but also want to ensure no container can request more than 1 CPU or 1Gi memory. Which LimitRange YAML snippet correctly enforces this?

hard

A. apiVersion: v1\nkind: LimitRange\nmetadata:\n name: resource-limits\nspec:\n limits:\n - default:\n cpu: 200m\n memory: 512Mi\n max:\n cpu: 1\n memory: 1Gi\n type: Container

B. apiVersion: v1\nkind: LimitRange\nmetadata:\n name: resource-limits\nspec:\n limits:\n - defaultRequest:\n cpu: 200m\n memory: 512Mi\n maxLimit:\n cpu: 1\n memory: 1Gi\n type: Container

C. apiVersion: v1\nkind: LimitRange\nmetadata:\n name: resource-limits\nspec:\n limits:\n - defaultCpu:\n cpu: 200m\n memory: 512Mi\n maxCpu:\n cpu: 1\n memory: 1Gi\n type: Container

D. apiVersion: v1\nkind: LimitRange\nmetadata:\n name: resource-limits\nspec:\n limits:\n - default:\n cpu: 200m\n memory: 512Mi\n maxRequest:\n cpu: 1\n memory: 1Gi\n type: Container

Solution

1. Step 1: Identify correct keys for defaults and max

   The correct keys are default for default requests and max for maximum allowed resources under limits.

2. Step 2: Validate YAML structure

   apiVersion: v1\nkind: LimitRange\nmetadata:\n name: resource-limits\nspec:\n limits:\n - default:\n cpu: 200m\n memory: 512Mi\n max:\n cpu: 1\n memory: 1Gi\n type: Container correctly uses default and max keys with proper resource names and type: Container.

3. Step 3: Check other options for invalid keys

   Options B, C, and D use invalid keys like defaultRequest, maxLimit, defaultCpu, or maxRequest which are not valid in LimitRange spec.

4. Final Answer:

   Option A correctly enforces default and max resource limits -> Option A

5. Quick Check:

   Use 'default' and 'max' keys for defaults and max limits [OK]

Hint: Use 'default' and 'max' keys under limits for defaults and max limits [OK]

Common Mistakes:

• Using invalid keys like defaultRequest or maxLimit
• Mixing up default and max keys
• Incorrect YAML indentation or structure