CKA Practice Question: Cluster Architecture, Installation and Configuration
This CKA practice question tests your understanding of cluster architecture, installation and configuration. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
You are setting up a new Kubernetes cluster using kubeadm. You run 'kubeadm init --pod-network-cidr=10.244.0.0/16' on the control plane node. The command fails with: '[preflight] Some fatal errors occurred: [ERROR CRI]: container runtime is not running: output: time="..." level=fatal msg="validate service connection: CRI v1 runtime API is not implemented for endpoint 'unix:///var/run/containerd/containerd.sock': rpc error: code = Unimplemented desc = unknown service runtime.v1.RuntimeService'"'. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The containerd runtime does not support the CRI v1 API; it may be an older version that only supports v1alpha2
The error message indicates that the containerd socket is reachable but the CRI v1 API (runtime.v1.RuntimeService) is not implemented. This typically occurs when containerd is an older version that only supports the CRI v1alpha2 API. Kubernetes 1.24+ defaults to the CRI v1 API, so an older containerd without v1 support will fail during kubeadm init.
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.
The kubelet version is incompatible with containerd
Why it's wrong here
The issue is the API version mismatch, not kubelet version.
✓
The containerd runtime does not support the CRI v1 API; it may be an older version that only supports v1alpha2
Why this is correct
Containerd versions prior to 1.6.0 use v1alpha2; later versions use v1. The kubelet in newer Kubernetes expects v1.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The containerd service is not running
Why it's wrong here
The error shows the endpoint exists but the API version is not implemented.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the error means the container runtime is not running at all (Option D), but the detailed error message clearly indicates the socket is reachable and the issue is an API version mismatch, not a service outage.
Trap categories for this question
Command / output trap
The error shows the endpoint exists but the API version is not implemented.
Detailed technical explanation
How to think about this question
Kubernetes 1.24 removed the built-in dockershim and requires a CRI-compliant runtime. The CRI v1 API was stabilized in Kubernetes 1.23 and became the default in 1.24. Older containerd versions (e.g., 1.4.x) only implement the v1alpha2 API, which is deprecated. To fix this, either upgrade containerd to v1.6.0+ (which supports both v1 and v1alpha2) or downgrade Kubernetes to a version that defaults to v1alpha2. The kubeadm preflight check explicitly probes the CRI API version, causing the failure.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CKA question in full detail.
Cluster Architecture, Installation and Configuration — This question tests Cluster Architecture, Installation and Configuration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The containerd runtime does not support the CRI v1 API; it may be an older version that only supports v1alpha2 — The error message indicates that the containerd socket is reachable but the CRI v1 API (runtime.v1.RuntimeService) is not implemented. This typically occurs when containerd is an older version that only supports the CRI v1alpha2 API. Kubernetes 1.24+ defaults to the CRI v1 API, so an older containerd without v1 support will fail during kubeadm init.
What should I do if I get this CKA question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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