CKA Practice Question: Cluster Architecture, Installation & Configuration
This CKA practice question tests your understanding of cluster architecture, installation & configuration. 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.
Network Topology
Refer to the exhibit. A Kubernetes cluster was initialized using kubeadm with the command shown. After initialization, the cluster nodes are in NotReady state. Which is the most likely missing step?
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.
Increase the apiserver-advertise-address to match the node's external IP.
Why wrong: Incorrect. The advertise address is already set to a valid IP. NotReady state is not caused by this.
B
Install a pod network add-on such as Flannel.
Correct. After kubeadm init, a pod network must be installed to enable communication between pods. Nodes remain NotReady until a CNI plugin is deployed.
C
Run kubeadm join on the control plane node.
Why wrong: Incorrect. kubeadm join is only for worker nodes, not the control plane node.
D
Restart the kubelet service on all nodes.
Why wrong: Incorrect. Restarting kubelet may temporarily fix issues but not the root cause. The missing pod network is the primary reason.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Install a pod network add-on such as Flannel.
The kubeadm init command only initializes the control plane. To make the nodes ready, a pod network must be installed. The exhibit shows no pod network add-on being applied, and the --pod-network-cidr flag indicates a specific CIDR for the pod network (10.244.0.0/16) which is typically used with Flannel. Without installing a CNI plugin, nodes remain NotReady.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Increase the apiserver-advertise-address to match the node's external IP.
Why it's wrong here
Incorrect. The advertise address is already set to a valid IP. NotReady state is not caused by this.
✓
Install a pod network add-on such as Flannel.
Why this is correct
Correct. After kubeadm init, a pod network must be installed to enable communication between pods. Nodes remain NotReady until a CNI plugin is deployed.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Incorrect. kubeadm join is only for worker nodes, not the control plane node.
✗
Restart the kubelet service on all nodes.
Why it's wrong here
Incorrect. Restarting kubelet may temporarily fix issues but not the root cause. The missing pod network is the primary reason.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CKA question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related CKA subnetting questions on CIDR, address ranges, and subnet selection.
The correct answer is: Install a pod network add-on such as Flannel. — The kubeadm init command only initializes the control plane. To make the nodes ready, a pod network must be installed. The exhibit shows no pod network add-on being applied, and the --pod-network-cidr flag indicates a specific CIDR for the pod network (10.244.0.0/16) which is typically used with Flannel. Without installing a CNI plugin, nodes remain NotReady.
What should I do if I get this CKA question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related CKA subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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