This DVA-C02 practice question tests your understanding of deployment. 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 developer is using AWS CloudFormation to deploy a stack that includes an Amazon RDS DB instance. The developer wants to update the stack to change the DB instance class. The update fails because CloudFormation cannot modify the DB instance class without replacement. The developer needs to complete the update with minimal downtime. What should the developer do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a custom resource with an AWS Lambda function to perform the modification, ensuring data is backed up and downtime is minimized.
Option B is correct because a custom resource backed by an AWS Lambda function allows you to perform the RDS DB instance class modification outside of CloudFormation's direct lifecycle, enabling you to use the 'ApplyImmediately' parameter to minimize downtime. CloudFormation's native update for RDS DB instance class requires replacement (i.e., a new physical resource), which causes downtime; a custom resource can orchestrate a 'modify-db-instance' API call with '--apply-immediately' to change the class in-place with only a brief reboot.
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.
✗
Delete the stack and create a new stack with the new DB instance class.
Why it's wrong here
Deleting the stack causes downtime and data loss unless a final snapshot is taken.
✓
Use a custom resource with an AWS Lambda function to perform the modification, ensuring data is backed up and downtime is minimized.
Why this is correct
A custom resource can orchestrate the change with minimal downtime, e.g., by creating a read replica and promoting it.
Related concept
Read the scenario before looking for a memorised answer.
✗
Update the stack and disable rollback on failure.
Why it's wrong here
Disabling rollback does not solve the modification issue; the update will still fail.
✗
Update the stack using a change set, then execute it.
Why it's wrong here
CloudFormation will attempt to modify the DB instance class, which requires replacement and causes downtime.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a change set (Option D) can bypass CloudFormation's replacement requirement, but change sets only preview and execute the same update logic—they do not change the underlying resource behavior.
Detailed technical explanation
How to think about this question
Under the hood, RDS DB instance class modifications are not supported as in-place updates in CloudFormation because the resource's physical ID changes when the instance class is altered, triggering a replacement. A custom resource with Lambda can call the 'modify-db-instance' API with '--apply-immediately' to perform the change with a brief reboot (typically 1-2 minutes), and you can use a 'DependsOn' and 'DeletionPolicy' to manage the stack lifecycle. In real-world scenarios, this approach is used for zero-downtime blue/green deployments by first creating a read replica, promoting it, and then switching DNS.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Deployment — This question tests Deployment — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a custom resource with an AWS Lambda function to perform the modification, ensuring data is backed up and downtime is minimized. — Option B is correct because a custom resource backed by an AWS Lambda function allows you to perform the RDS DB instance class modification outside of CloudFormation's direct lifecycle, enabling you to use the 'ApplyImmediately' parameter to minimize downtime. CloudFormation's native update for RDS DB instance class requires replacement (i.e., a new physical resource), which causes downtime; a custom resource can orchestrate a 'modify-db-instance' API call with '--apply-immediately' to change the class in-place with only a brief reboot.
What should I do if I get this DVA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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