KCNA Container Orchestration Practice Question
Which THREE are valid container runtimes that implement the Kubernetes CRI? (Choose three.)
⚠ Common exam trap
KCNA often tests the confusion between CRI implementations (containerd, CRI-O, dockershim) and OCI runtimes (runc, crun) — candidates incorrectly pick runc because it 'runs containers'.
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
✓
Docker (via dockershim, deprecated)
Docker (via dockershim) is correct because Kubernetes historically shipped an in-tree CRI adapter called dockershim that translated CRI calls to the Docker Engine API, allowing Docker to serve as a container runtime until its deprecation in v1.24. containerd is correct because it natively implements the CRI plugin (cri plugin enabled by default), making it a first-class Kubernetes container runtime. CRI-O is correct because it was purpose-built as a lightweight CRI implementation for Kubernetes using OCI-compliant runtimes like runc. runc is not a CRI implementation; it is a low-level OCI runtime invoked by higher-level runtimes such as containerd and CRI-O to actually create containers. rkt is not a CRI runtime; it was an alternative container engine that was deprecated and never implemented the Kubernetes CRI.
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 (via dockershim, deprecated)
Why this is correct
Docker's CRI support came only through dockershim, an in-tree adapter that Kubernetes removed in v1.24. It still counts as a valid CRI-implementing runtime historically, satisfying the stem, though the deprecation means containerd or CRI-O is now preferred.
- ✓
containerd
Why this is correct
containerd implements the Kubernetes Container Runtime Interface directly, exposing the CRI gRPC service that kubelet calls to manage pod sandboxes and containers. It satisfies the stem's requirement for a valid CRI runtime, running containers via runc without Docker's daemon layer.
- ✗
runc
Why it's wrong here
runc is an OCI low-level runtime invoked by CRI implementations such as containerd, not itself a CRI runtime. It tempts because runc underpins nearly every Kubernetes node, so it appears central, yet it sits below the CRI boundary.
- ✓
CRI-O
Why this is correct
CRI-O is a lightweight runtime built specifically to implement the Kubernetes Container Runtime Interface, using OCI-compliant images and runc. It satisfies the stem directly: it is a valid CRI-implementing runtime, not a shim or orchestrator.
- ✗
rkt
Why it's wrong here
rkt was deprecated and its CRI shim abandoned, so it no longer implements the CRI in supported Kubernetes releases. It tempts because rkt was a genuine early container runtime with CRI support, and would qualify only on legacy clusters predating its retirement.
Go deeper
Related to this question
Learn chapter
Container Orchestration Essentials
Key term
Container Runtime Interface
The Container Runtime Interface (CRI) is a standardized plugin protocol that allows Kubernetes to work with different container runtimes without needing to change its core code.
Key term
ReplicaSet and Replication
A ReplicaSet ensures a specified number of identical pod instances are running at all times in Kubernetes, using replication to maintain availability and stability.
About these practice questions
This KCNA question is part of Courseiva's 930-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CNCF exam blueprint
This KCNA 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 KCNA exam.