The correct answer is to configure the Aurora cluster's security group to allow inbound traffic from the EC2 instances' security group. This works because security groups act as a virtual firewall at the instance level, and you can reference another security group as the source, which dynamically grants access to any EC2 instance that belongs to that group—even if the instance’s IP changes. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of network-level access control versus authentication mechanisms; a common trap is confusing IAM database authentication (which controls who can log in, not where they connect from) with security group rules. Remember that for restricting network access to specific EC2 instances within the same VPC, security group chaining is the precise and granular solution, while NACLs are stateless and less suitable for this use case. Memory tip: think “SG-to-SG” for instance-level access control—if the source is a security group ID, traffic is allowed from any resource in that group.
DBS-C01 Database Security Practice Question
This DBS-C01 practice question tests your understanding of database 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 company is using Amazon Aurora MySQL-Compatible Edition. The security team wants to restrict access to the database so that only specific applications running on Amazon EC2 instances can connect. The EC2 instances are in the same VPC as the Aurora cluster. Which combination of steps should be taken to enforce this restriction?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure the Aurora cluster's security group to allow inbound traffic from the EC2 instances' security group.
Option A is correct because security groups can be used to allow traffic only from specific security groups (e.g., EC2 security group). Option B is wrong because IAM database authentication controls user authentication, not network access. Option C is wrong because NACLs are stateless and less granular. Option D is wrong because subnet group does not restrict access.
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.
✗
Enable IAM database authentication and create database users for each application.
Why it's wrong here
This controls authentication, not network access.
✗
Modify the DB subnet group to include only subnets where the EC2 instances reside.
Why it's wrong here
Subnet group does not restrict access at the instance level.
✗
Use a network ACL to allow traffic only from the EC2 instances' IP addresses.
Why it's wrong here
NACLs are stateless and less flexible than security groups.
✓
Configure the Aurora cluster's security group to allow inbound traffic from the EC2 instances' security group.
Why this is correct
Security group rules can reference other security groups.
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 DBS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Database Security — This question tests Database Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Configure the Aurora cluster's security group to allow inbound traffic from the EC2 instances' security group. — Option A is correct because security groups can be used to allow traffic only from specific security groups (e.g., EC2 security group). Option B is wrong because IAM database authentication controls user authentication, not network access. Option C is wrong because NACLs are stateless and less granular. Option D is wrong because subnet group does not restrict access.
What should I do if I get this DBS-C01 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 DBS-C01 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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