The answer is to check the CloudFormation stack events for a detailed status message from the DBInstance resource. This is the correct first step because when a CloudFormation RDS creation failure occurs, the stack events provide the specific error reason from the RDS API, such as an invalid DB instance class that is not supported in the chosen region, which is the most common cause of failure. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this tests your understanding of the CloudFormation troubleshooting workflow, emphasizing that stack events are the most direct source of failure details, more so than checking the RDS console or adjusting timeouts. A common trap is jumping to VPC configuration or timeout adjustments, but the event log immediately reveals validation errors like unsupported instance types. Remember the mnemonic: "Events first, fix the worst"—always check the stack events for the precise error before making any changes.
DOP-C02 SDLC Automation Practice Question
This DOP-C02 practice question tests your understanding of sdlc automation. 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 uses AWS CloudFormation to manage infrastructure. They have a stack that creates an Amazon RDS instance. The stack creation fails with the error: 'The following resource(s) failed to create: [DBInstance]'. The CloudFormation template includes a parameter for the DB instance class. Which troubleshooting step should be taken 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Check the CloudFormation stack events for a detailed status message from the DBInstance resource.
Option B is correct because the most common reason for RDS creation failure is an invalid instance class (e.g., not available in the region). Option A is wrong because the VPC configuration is less likely. Option C is wrong because checking the RDS console will show the error, but checking the events is more direct. Option D is wrong because increasing timeout won't fix a configuration error.
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 stack creation timeout to allow more time for the database to be created.
Why it's wrong here
Timeout is not the issue if the error is immediate.
✓
Check the CloudFormation stack events for a detailed status message from the DBInstance resource.
Why this is correct
Stack events provide the specific reason for failure, such as 'DBInstance class not supported'.
Clue confirmation
The clue word "first" in the question point toward this answer.
Verify that the VPC has at least two public subnets in different Availability Zones.
Why it's wrong here
RDS does not require public subnets; it can be in private subnets.
✗
Use the Amazon RDS console to check if a DB instance with the same identifier already exists.
Why it's wrong here
While possible, the stack events are more immediate and specific.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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 DOP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
SDLC Automation — This question tests SDLC Automation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Check the CloudFormation stack events for a detailed status message from the DBInstance resource. — Option B is correct because the most common reason for RDS creation failure is an invalid instance class (e.g., not available in the region). Option A is wrong because the VPC configuration is less likely. Option C is wrong because checking the RDS console will show the error, but checking the events is more direct. Option D is wrong because increasing timeout won't fix a configuration error.
What should I do if I get this DOP-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 DOP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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