ANS-C01 Network Design Practice Question
A company has a VPC with a public subnet and a private subnet. The private subnet contains Amazon RDS instances that should only be accessed by EC2 instances in the same VPC. The EC2 instances are in a security group named 'App-SG'. Which configuration will meet the requirement?
⚠ Common exam trap
Candidates often confuse security groups with network ACLs, or assume that allowing the VPC CIDR is sufficient, not realizing that security group references provide more precise, instance-level access control than CIDR-based rules.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure a security group on the RDS instances to allow inbound traffic from the 'App-SG' security group.
Security groups are stateful and can reference other security groups as a source, allowing traffic from all instances associated with the source security group. By configuring the RDS security group to allow inbound traffic from 'App-SG', only EC2 instances in that group can access the RDS instances, meeting the requirement without exposing the database to the entire VPC CIDR.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure a network ACL on the private subnet to allow inbound traffic from the VPC CIDR.
Why it's wrong here
This is broad and does not restrict to App-SG.
- ✗
Configure a network ACL on the private subnet to allow inbound traffic from the public subnet CIDR.
Why it's wrong here
This would allow traffic from the public subnet, not specifically from App-SG.
- ✓
Configure a security group on the RDS instances to allow inbound traffic from the 'App-SG' security group.
Why this is correct
Security group referencing another security group allows only instances with that security group.
- ✗
Configure a security group on the RDS instances to allow inbound traffic from the VPC CIDR.
Why it's wrong here
This allows any instance in the VPC, not just App-SG.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.