- A
The accounts are in different OUs and the stack set is not configured to deploy to all OUs.
Why wrong: Stack sets can be deployed to multiple OUs, and the update succeeded for most accounts, indicating the stack set is correctly configured.
- B
Some accounts have manually created resources that conflict with the stack set template's resources.
If a resource with the same logical ID already exists outside the stack, CloudFormation cannot update the stack and throws an error.
- C
The network team does not have sufficient IAM permissions to update stacks in those accounts.
Why wrong: If permissions were insufficient, the operation would fail with an access denied error, not a resource exists error.
- D
The stack set was previously drift-detected and the drift is preventing updates.
Why wrong: Drift detection does not block updates; it just reports differences.
Quick Answer
The answer is that some accounts have manually created resources that conflict with the stack set template's resources. This is the most likely cause because CloudFormation StackSets apply a single template across multiple accounts, and each resource in the template is assigned a unique logical ID. When the stack set update attempts to create a new subnet with a logical ID that already exists in an account—due to a previous manual creation or a separate deployment—the operation fails with a resource conflict error, as CloudFormation cannot create a duplicate resource with the same identifier. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of StackSet idempotency and the importance of managing resources exclusively through Infrastructure as Code to avoid drift. A common trap is assuming the failure is due to permissions or organizational unit structure, but the core issue is always resource name collision. Memory tip: think of StackSets as a single blueprint—if someone else has already built a wall where your blueprint says to build one, the construction stops.
SAP-C02 Practice Question: Design Solutions for Organizational Complexity
This SAP-C02 practice question tests your understanding of design solutions for organizational complexity. 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.
A company has a multi-account AWS environment using AWS Organizations with 50 accounts. The accounts are organized into OUs based on environment: Production, Staging, and Development. The central IT team uses AWS CloudFormation StackSets to deploy a baseline network configuration (VPC, subnets, security groups) to all accounts. Recently, the network team updated the stack set to add a new subnet to the VPC. After the update, they noticed that the stack set operation failed for 10 accounts. The error message indicates that the stack set cannot update because a resource already exists. What is the MOST LIKELY cause of this failure?
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 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
Some accounts have manually created resources that conflict with the stack set template's resources.
Option C is correct because StackSets use a single template, and if an account already has a resource with the same logical ID (e.g., due to a previous manual creation), the update fails. Option A is wrong because stack set updates can be performed with proper permissions. Option B is wrong because StackSets can manage resources across OUs, but the issue is resource conflict. Option D is wrong because drift does not prevent updates; it would be detected separately.
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.
- ✗
The accounts are in different OUs and the stack set is not configured to deploy to all OUs.
Why it's wrong here
Stack sets can be deployed to multiple OUs, and the update succeeded for most accounts, indicating the stack set is correctly configured.
- ✓
Some accounts have manually created resources that conflict with the stack set template's resources.
Why this is correct
If a resource with the same logical ID already exists outside the stack, CloudFormation cannot update the stack and throws an error.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
- ✗
The network team does not have sufficient IAM permissions to update stacks in those accounts.
Why it's wrong here
If permissions were insufficient, the operation would fail with an access denied error, not a resource exists error.
- ✗
The stack set was previously drift-detected and the drift is preventing updates.
Why it's wrong here
Drift detection does not block updates; it just reports differences.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SAP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
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Design Solutions for Organizational Complexity — study guide chapter
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FAQ
Questions learners often ask
What does this SAP-C02 question test?
Design Solutions for Organizational Complexity — This question tests Design Solutions for Organizational Complexity — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Some accounts have manually created resources that conflict with the stack set template's resources. — Option C is correct because StackSets use a single template, and if an account already has a resource with the same logical ID (e.g., due to a previous manual creation), the update fails. Option A is wrong because stack set updates can be performed with proper permissions. Option B is wrong because StackSets can manage resources across OUs, but the issue is resource conflict. Option D is wrong because drift does not prevent updates; it would be detected separately.
What should I do if I get this SAP-C02 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 SAP-C02 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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Last reviewed: Jun 20, 2026
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