This CKA practice question tests your understanding of cluster architecture, installation & 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.
An administrator is tasked with setting up a new Kubernetes cluster using kubeadm. They have two nodes: one control plane and one worker. After initializing the control plane with 'kubeadm init', the worker node fails to join with the error 'error execution phase preflight: [preflight] Some fatal errors occurred: [ERROR CRI]: container runtime is not running'. What should the administrator check first?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Ensure that containerd is installed and running on the worker node.
The CRI error indicates the runtime is not running.
Verify that the control plane node is healthy.
Why wrong: The error is on the worker node.
Check if the join token has expired.
Why wrong: Token expiry would give a different error.
Install a network plugin like Calico on the control plane.
Why wrong: Network plugin is not related to CRI error.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Ensure that containerd is installed and running on the worker node.
The error 'container runtime is not running' on the worker node indicates that the CRI (Container Runtime Interface) implementation, typically containerd, is not active. Since kubelet relies on a running container runtime to manage pods, the administrator must first check that containerd is installed and running on the worker node using commands like 'systemctl status containerd' or 'systemctl start containerd'.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Ensure that containerd is installed and running on the worker node.
Why this is correct
The CRI error indicates the runtime is not running.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Verify that the control plane node is healthy.
Why it's wrong here
The error is on the worker node.
Check if the join token has expired.
Why it's wrong here
Token expiry would give a different error.
Install a network plugin like Calico on the control plane.
Why it's wrong here
Network plugin is not related to CRI error.
Common exam traps
The trap here is that candidates often assume the error is related to the control plane or networking, but the CRI error specifically points to a missing or stopped container runtime on the node attempting to join.
Detailed technical explanation
The kubelet on each node communicates with the container runtime via the CRI socket (e.g., /run/containerd/containerd.sock). If containerd is not running, the kubelet cannot create the pause container needed for pod sandboxes, causing the preflight check to fail. In real-world scenarios, a common subtlety is that containerd may be installed but its socket path is misconfigured in the kubelet's config file (e.g., /var/lib/kubelet/config.yaml), leading to the same error even if the service is active.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the CKA 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
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FAQ
Cluster Architecture, Installation & Configuration — This question tests Cluster Architecture, Installation & Configuration — Read the scenario before looking for a memorised answer..
The correct answer is: Ensure that containerd is installed and running on the worker node. — The error 'container runtime is not running' on the worker node indicates that the CRI (Container Runtime Interface) implementation, typically containerd, is not active. Since kubelet relies on a running container runtime to manage pods, the administrator must first check that containerd is installed and running on the worker node using commands like 'systemctl status containerd' or 'systemctl start containerd'.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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