The answer is two reasons: a DeletionPolicy of 'Retain' on the DB instance, and an unsupported DB engine version for the storage type migration. When CloudFormation attempts a storage type modification from gp2 to io1 that requires resource replacement, the 'Retain' DeletionPolicy blocks the update because CloudFormation cannot delete and recreate a resource it is instructed to preserve. Additionally, certain older or specific DB engine versions do not support the underlying migration needed to change storage types, causing the modification to fail even if the request is syntactically valid. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this question tests your understanding of CloudFormation's replacement behavior and RDS engine compatibility—a common trap is assuming all storage changes are in-place modifications. Remember that replacement-triggering updates are incompatible with 'Retain', and always verify engine version support for storage migrations. Memory tip: "Retain blocks replace, engine blocks migrate."
SOA-C02 Deployment, Provisioning, and Automation Practice Question
This SOA-C02 practice question tests your understanding of deployment, provisioning, and 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 SysOps administrator is troubleshooting a failed AWS CloudFormation stack update. The update attempted to modify an Amazon RDS DB instance's storage type from gp2 to io1. The error message indicates that the modification is not supported. Which TWO reasons could cause this error? (Choose TWO.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The DB instance is using an Oracle DB engine version that does not support storage type modification.
Option A is correct because CloudFormation stack updates that require replacement will fail if 'DeletionPolicy' is set to 'Retain' and the resource is replaced. Option C is correct because some storage modifications require a migration that is not supported for certain DB engine versions. Option B is wrong because storage type changes are generally allowed without enabling backup. Option D is wrong because maintenance windows do not affect the feasibility of modification. Option E is wrong because the allocated storage size can be changed during modification.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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 DB instance is using an Oracle DB engine version that does not support storage type modification.
Why this is correct
Some older engine versions have limitations.
Related concept
Standard ACLs match source addresses.
✗
The DB instance does not have automated backups enabled.
Why it's wrong here
Automated backups are not required for storage type changes.
✓
The DB instance has a DeletionPolicy of 'Retain', and the update requires replacement.
Why this is correct
If the modification requires replacement, the DeletionPolicy prevents it.
Related concept
Standard ACLs match source addresses.
✗
The stack update is occurring during the DB instance's maintenance window.
Why it's wrong here
Maintenance windows affect timing, not feasibility.
✗
The allocated storage size is below the minimum required for io1.
Why it's wrong here
Minimum size for io1 is 100 GB, but this can be changed.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related SOA-C02 ACL questions on filtering logic and placement.
Deployment, Provisioning, and Automation — This question tests Deployment, Provisioning, and Automation — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The DB instance is using an Oracle DB engine version that does not support storage type modification. — Option A is correct because CloudFormation stack updates that require replacement will fail if 'DeletionPolicy' is set to 'Retain' and the resource is replaced. Option C is correct because some storage modifications require a migration that is not supported for certain DB engine versions. Option B is wrong because storage type changes are generally allowed without enabling backup. Option D is wrong because maintenance windows do not affect the feasibility of modification. Option E is wrong because the allocated storage size can be changed during modification.
What should I do if I get this SOA-C02 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related SOA-C02 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Question Discussion
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