The answer is to create a snapshot of the unencrypted instance, copy the snapshot with encryption enabled, and restore the encrypted snapshot to a new DB instance. This is necessary because RDS does not support enabling encryption on an existing, running instance; encryption at rest must be applied at the time of instance creation or through a snapshot migration. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of the immutable nature of RDS encryption and how service control policies (SCPs) can mandate encryption but cannot retroactively fix unencrypted resources. A common trap is assuming you can simply modify the existing instance or toggle encryption on the subnet group, but neither affects data at rest. Remember the memory tip: “Snap, Copy, Restore” — you cannot encrypt in place, so you must snapshot, encrypt the copy, and rebuild.
SCS-C02 Management and Security Governance Practice Question
This SCS-C02 practice question tests your understanding of management and security governance. 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's security team needs to enforce encryption at rest for all RDS instances in the production account. They have enabled mandatory encryption using a service control policy. What else must be done to ensure existing unencrypted RDS instances are encrypted?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a snapshot of the unencrypted instance, copy the snapshot with encryption enabled, and restore the encrypted snapshot to a new DB instance.
Option A is correct because RDS does not support encrypting existing unencrypted instances; you must create a snapshot, copy it encrypted, and restore. Option B is incorrect because you cannot enable encryption on an existing instance. Option C is incorrect because enabling encryption on the DB subnet group does not affect existing instances. Option D is incorrect because you must use a snapshot copy.
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.
✗
Attach a new KMS key policy to the RDS instance.
Why it's wrong here
Key policy does not encrypt the instance.
✓
Create a snapshot of the unencrypted instance, copy the snapshot with encryption enabled, and restore the encrypted snapshot to a new DB instance.
Why this is correct
This is the standard procedure to migrate to encrypted RDS.
Enable encryption on the DB subnet group and reboot the instance.
Why it's wrong here
Encryption is not configured at subnet group level.
✗
Modify the RDS instance to enable encryption using the AWS Console.
Why it's wrong here
RDS does not allow enabling encryption on existing instances.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
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 SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Management and Security Governance — This question tests Management and Security Governance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Create a snapshot of the unencrypted instance, copy the snapshot with encryption enabled, and restore the encrypted snapshot to a new DB instance. — Option A is correct because RDS does not support encrypting existing unencrypted instances; you must create a snapshot, copy it encrypted, and restore. Option B is incorrect because you cannot enable encryption on an existing instance. Option C is incorrect because enabling encryption on the DB subnet group does not affect existing instances. Option D is incorrect because you must use a snapshot copy.
What should I do if I get this SCS-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 SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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