This ANS-C01 practice question tests your understanding of network design. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 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?
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related concept
Read the scenario before looking for a memorised answer.
✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that 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.
Detailed technical explanation
How to think about this question
Security group rules using source security group references are evaluated based on the private IP addresses of the instances in the source group, and the stateful nature of security groups means return traffic is automatically allowed. This approach is more granular than CIDR-based rules and is recommended for multi-tier architectures where you want to restrict database access to specific application tiers. In contrast, network ACLs operate at the subnet boundary and require explicit inbound and outbound rules, making them less suitable for instance-level access control.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this ANS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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