Quality of Service classes (Guaranteed, Burstable, BestEffort) in Kubernetes - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are the three Quality of Service (QoS) classes in Kubernetes?

The three QoS classes are Guaranteed, Burstable, and BestEffort. They define how Kubernetes manages pod resources under pressure.

intermediate

What conditions must a pod meet to be classified as Guaranteed QoS in Kubernetes?

A pod is Guaranteed if every container has memory and CPU requests equal to their limits. This means the pod gets the highest priority for resources.

intermediate

Describe the <strong>Burstable</strong> QoS class in Kubernetes.

A pod is Burstable if it has resource requests and limits set, but requests are less than limits for at least one resource. It can use extra resources when available but may be throttled under pressure.

beginner

What happens to a BestEffort pod during resource contention in Kubernetes?

BestEffort pods have no resource requests or limits set. They get the lowest priority and are the first to be evicted when the node runs out of resources.

intermediate

How does Kubernetes determine the QoS class of a pod?

Kubernetes checks the resource requests and limits of all containers in the pod. Based on their presence and equality, it assigns the pod to Guaranteed, Burstable, or BestEffort.

Which QoS class in Kubernetes guarantees the highest priority for resource allocation?

A None

B Burstable

C BestEffort

D Guaranteed

The Guaranteed class ensures pods have equal resource requests and limits, giving them the highest priority.

A pod with no resource requests or limits set falls under which QoS class?

A BestEffort

B Guaranteed

C Burstable

D Critical

Pods without any resource requests or limits are classified as BestEffort.

If a pod has CPU requests less than CPU limits, what QoS class does it belong to?

A Burstable

B BestEffort

C Guaranteed

D None

When requests are less than limits, the pod is Burstable.

Which QoS class pods are evicted first during node resource pressure?

A Guaranteed

B BestEffort

C All equally

D Burstable

BestEffort pods have the lowest priority and are evicted first.

What must be true for a pod to be classified as Guaranteed?

A Requests less than limits for some containers

B No resource requests or limits

C Requests equal limits for all containers

D Only CPU requests set

Guaranteed requires requests and limits to be equal for every container.

Explain the differences between Guaranteed, Burstable, and BestEffort QoS classes in Kubernetes.

Think about resource requests and limits and how Kubernetes uses them to prioritize pods.

Describe how Kubernetes uses QoS classes to manage pod eviction during resource shortages.

Consider which pods have resource guarantees and which do not.

Practice

1. Which Kubernetes Quality of Service (QoS) class guarantees that a pod will always get the resources it requests?

easy

A. Burstable

B. Guaranteed

C. BestEffort

D. Reserved

Solution

1. Step 1: Understand QoS classes in Kubernetes

   There are three main QoS classes: Guaranteed, Burstable, and BestEffort. Guaranteed means the pod has resource requests equal to limits.

2. Step 2: Identify which class ensures resource guarantees

   Guaranteed pods always get the resources they request because requests and limits match exactly.

3. Final Answer:

   Guaranteed -> Option B

4. Quick Check:

   Guaranteed = full resource guarantee [OK]

Hint: Guaranteed means requests equal limits, so full resource guarantee [OK]

Common Mistakes:

• Confusing Burstable with Guaranteed
• Thinking BestEffort has resource guarantees
• Assuming Reserved is a QoS class

2. Which of the following pod resource specifications will result in a Burstable QoS class?

easy

A. resources:\n requests:\n cpu: '200m'\n memory: '128Mi'\n limits:\n cpu: '500m'\n memory: '256Mi'

B. resources:\n requests:\n cpu: '500m'\n memory: '256Mi'\n limits:\n cpu: '500m'\n memory: '256Mi'

C. resources:\n requests:\n cpu: '0'\n memory: '0'\n limits:\n cpu: '0'\n memory: '0'

D. resources: {}

Solution

1. Step 1: Review resource requests and limits for QoS classes

   Guaranteed requires requests equal to limits. Burstable requires requests less than limits. BestEffort has no requests or limits.

2. Step 2: Match the given specs to Burstable

   resources:\n requests:\n cpu: '200m'\n memory: '128Mi'\n limits:\n cpu: '500m'\n memory: '256Mi' has requests less than limits, so it is Burstable.

3. Final Answer:

   requests less than limits -> Option A

4. Quick Check:

   Burstable = requests < limits [OK]

Hint: Burstable means requests less than limits, not equal [OK]

Common Mistakes:

• Choosing equal requests and limits as Burstable
• Assuming empty resources means Burstable
• Confusing zero requests with BestEffort

3. Given this pod spec snippet, what QoS class will Kubernetes assign?

resources:
  requests:
    cpu: '100m'
    memory: '128Mi'
  limits:
    cpu: '100m'
    memory: '128Mi'

medium

A. Burstable

B. BestEffort

C. null

D. Guaranteed

Solution

1. Step 1: Compare requests and limits in the pod spec

   Requests and limits for both CPU and memory are equal (100m CPU and 128Mi memory).

2. Step 2: Determine QoS class based on equality

   When requests equal limits for all resources, Kubernetes assigns Guaranteed QoS.

3. Final Answer:

   Guaranteed -> Option D

4. Quick Check:

   Requests = Limits means Guaranteed [OK]

Hint: Equal requests and limits means Guaranteed QoS [OK]

Common Mistakes:

• Choosing Burstable when requests equal limits
• Thinking BestEffort applies with resource specs
• Selecting null as a QoS class

4. Given this pod spec snippet, what QoS class will Kubernetes assign?

resources:
  requests:
    cpu: '0'
    memory: '0'

medium

A. BestEffort

B. Burstable

C. Guaranteed

D. It will cause a syntax error

Solution

1. Step 1: Analyze the resource specification

   Requests are set to cpu: '0' and memory: '0', with no limits defined.

2. Step 2: Apply QoS classification rules

   Requests are specified but zero values are treated as no requests. No limits are defined. This qualifies as BestEffort, since no resource requests or limits are effectively set.

3. Final Answer:

   BestEffort -> Option A

4. Quick Check:

   No requests or limits means BestEffort [OK]

Hint: Zero requests with no limits -> BestEffort (not Burstable) [OK]

Common Mistakes:

• Thinking it causes a syntax error
• Assuming zero requests means BestEffort
• Believing it qualifies as Guaranteed

5. You want to ensure a pod gets guaranteed CPU and memory resources but also allow it to burst beyond the requested amount when available. Which resource configuration and QoS class combination achieves this?

hard

A. Set no requests or limits; QoS class BestEffort

B. Set requests equal to limits; QoS class Guaranteed

C. Set requests less than limits; QoS class Burstable

D. Set limits less than requests; QoS class Burstable

Solution

1. Step 1: Understand resource guarantees and bursting

   Guaranteed QoS requires requests equal to limits, which means no bursting beyond limits. Burstable allows requests less than limits, enabling bursting.

2. Step 2: Match configuration to desired behavior

   Setting requests less than limits gives minimum guaranteed resources with ability to burst, which is Burstable QoS.

3. Final Answer:

   Set requests less than limits; QoS class Burstable -> Option C

4. Quick Check:

   Burstable = guaranteed minimum + burst capacity [OK]

Hint: Burstable = requests less than limits for bursting [OK]

Common Mistakes:

• Choosing Guaranteed which disallows bursting
• Setting limits less than requests (invalid)
• Assuming BestEffort provides guarantees