The correct three steps are to launch the database in a private subnet, create a security group that allows inbound traffic on port 3306 from the EC2 instances' security group, and enable encryption at rest. This combination ensures that the RDS MySQL instance has no direct internet exposure, access is tightly scoped to only the specific EC2 resources via security group referencing rather than IP addresses, and data is protected against physical compromise. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of defense-in-depth for database workloads, where a common trap is choosing a public subnet for easier access or disabling encryption to reduce overhead—both of which violate the principle of least privilege and data protection. Remember the mnemonic "PSE": Private subnet, Security group referencing, and Encryption at rest form the triad for comprehensively securing RDS MySQL.
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 security engineer is tasked with securing an Amazon RDS for MySQL database. The database must be accessible only from a specific set of EC2 instances. Which THREE steps should the engineer take?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable encryption at rest for the RDS instance.
Option A is correct because launching the DB in a private subnet prevents direct internet access. Option B is correct because using a security group to allow inbound traffic from the EC2 instances' security group restricts access. Option D is correct because enabling encryption at rest protects data. Option C is wrong because a public subnet would expose the DB to the internet. Option E is wrong because disabling encryption is not a security measure.
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.
✗
Disable encryption at rest to improve performance.
Associate the RDS instance with a public subnet for easier access.
Why it's wrong here
Public subnet would expose the DB to the internet.
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 SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Infrastructure Security — This question tests Infrastructure Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Enable encryption at rest for the RDS instance. — Option A is correct because launching the DB in a private subnet prevents direct internet access. Option B is correct because using a security group to allow inbound traffic from the EC2 instances' security group restricts access. Option D is correct because enabling encryption at rest protects data. Option C is wrong because a public subnet would expose the DB to the internet. Option E is wrong because disabling encryption is not a security measure.
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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