CKS Minimize Microservice Vulnerabilities Practice Question
Which container runtime is specifically designed for sandboxing containers with a lightweight kernel?
⚠ Common exam trap
The CNCF CKS exam often tests the distinction between container runtimes that share the host kernel (like runc) and those that provide an additional isolation layer (like gVisor or Kata Containers), and candidates mistakenly pick containerd or Docker because they are more familiar names, not realizing they lack the lightweight kernel sandboxing feature.
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
✓
gVisor (runsc)
gVisor (runsc) is a container runtime that provides a lightweight kernel written in Go, which intercepts system calls from the container and handles them in user space. This creates a strong sandbox between the container and the host kernel, making it specifically designed for sandboxing containers with a lightweight kernel, unlike standard runtimes that share the host kernel directly.
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 a container platform that builds, ships, and runs applications, but its default runtime is runc, which uses the host kernel directly. Containers created by Docker share the kernel with the host, and while Docker can apply seccomp, AppArmor, or SELinux profiles for additional hardening, these do not create a sandbox or user-space kernel. Docker therefore provides process isolation, not sandboxing, making it the wrong choice for running untrusted code.
- ✗
containerd
Why it's wrong here
containerd is a high-level runtime that manages images and container lifecycle, but by default it delegates container execution to runc, which uses the host kernel. It is not designed as a sandbox; rather, it is a management layer that can actually be configured to use sandboxed runtimes like gVisor when running Kubernetes with the appropriate runtime class. Standard containerd containers share the host kernel, so they lack the isolation of a sandbox.
- ✓
gVisor (runsc)
Why this is correct
gVisor (runsc) is an OCI runtime that implements a user-space kernel, intercepting system calls made by the container and processing them in user space rather than passing them to the host kernel. This architecture significantly reduces the host kernel attack surface, making gVisor specifically designed for sandboxing and running untrusted workloads. The user-space kernel adds a layer of isolation that standard runtimes do not provide.
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runc
Why it's wrong here
runc is the reference OCI runtime that launches containers by directly setting up namespaces and cgroups and executing them using the host kernel. It is optimized for low overhead and performance, but it does not intercept syscalls or implement a separate kernel, so a vulnerability in the host kernel can escape the container. runc is a container runtime, not a sandbox runtime, making it incorrect for sandboxing requirements.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.