- A
docker
Why wrong: Docker is not a sandboxing runtime.
- B
runc
Why wrong: runc is the default runtime for OCI containers, not a sandbox.
- C
runsc
gVisor's runtime handler is runsc.
- D
containerd
Why wrong: containerd is a container runtime that uses runc by default.
- E
kata
Kata Containers uses kata as the runtime handler.
Question 768 of 997
Valid RuntimeClass Handlers for Container Sandboxing — Kubernetes Runtime Security | Certified Kubernetes Security Specialist Explained
This CKS practice question tests your understanding of minimize microservice vulnerabilities. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which TWO of the following are valid Kubernetes RuntimeClass handlers for container sandboxing? (Choose two.)
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
runsc
Option C (runsc) is correct because it is the handler for gVisor, a user-space kernel that provides an additional layer of sandboxing between the container and the host kernel. In Kubernetes, a RuntimeClass with handler 'runsc' instructs the container runtime (e.g., containerd) to launch the container using gVisor's runsc runtime, which intercepts system calls to enforce a security boundary.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
docker
Why it's wrong here
Docker is not a sandboxing runtime.
- ✗
runc
Why it's wrong here
runc is the default runtime for OCI containers, not a sandbox.
- ✓
runsc
Why this is correct
gVisor's runtime handler is runsc.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
containerd
Why it's wrong here
containerd is a container runtime that uses runc by default.
- ✓
kata
Why this is correct
Kata Containers uses kata as the runtime handler.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The CKS exam often tests the distinction between container runtimes (like runc) and sandboxing runtimes (like runsc or kata), and the trap here is that candidates mistakenly select runc because it is a common runtime, but it does not provide sandboxing isolation.
Detailed technical explanation
How to think about this question
gVisor's runsc implements a 2nd-level kernel (Sentry) that handles application system calls, reducing the attack surface of the host kernel. In contrast, Kata Containers (handler 'kata') uses lightweight VMs (e.g., QEMU or Firecracker) to provide hardware-virtualized isolation, each container running in its own guest kernel. Both runsc and kata are valid RuntimeClass handlers for sandboxing, but they achieve isolation through fundamentally different mechanisms—runsc via user-space kernel interception, kata via hardware virtualization.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the CKS exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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Minimize Microservice Vulnerabilities — study guide chapter
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FAQ
Questions learners often ask
What does this CKS question test?
Minimize Microservice Vulnerabilities — This question tests Minimize Microservice Vulnerabilities — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: runsc — Option C (runsc) is correct because it is the handler for gVisor, a user-space kernel that provides an additional layer of sandboxing between the container and the host kernel. In Kubernetes, a RuntimeClass with handler 'runsc' instructs the container runtime (e.g., containerd) to launch the container using gVisor's runsc runtime, which intercepts system calls to enforce a security boundary.
What should I do if I get this CKS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on CKS
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which TWO of the following are valid RuntimeClass handlers for container sandboxing?
easy- A.docker
- B.runc
- ✓ C.runsc
- D.crun
- ✓ E.kata
Why C: Option C is correct because `runsc` is the RuntimeClass handler for gVisor, a sandboxed container runtime that provides a user-space kernel to isolate containers from the host kernel. It intercepts system calls and implements a security boundary, making it a valid handler for container sandboxing.
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Last reviewed: Jul 4, 2026
This CKS practice question is part of Courseiva's free CNCF certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CKS exam.
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