- A
Add an inbound rule to the RDS security group that allows traffic from the VPC CIDR on port 3306.
Why wrong: This allows traffic from all instances in the VPC, which is too broad.
- B
Add an inbound rule to the RDS security group that allows traffic from the security group of the application server on port 3306.
This restricts access to only the application server's security group.
- C
Add an inbound rule to the RDS security group that allows traffic from the subnet CIDR of the application server on port 3306.
Why wrong: This allows any instance in that subnet, which may include other instances.
- D
Add an inbound rule to the RDS security group that allows traffic from 0.0.0.0/0 on port 3306.
Why wrong: This exposes the database to the internet.
Question 425 of 1,748
Security Group Referencing for Cross-Tier Traffic
This SCS-C02 practice question tests your understanding of infrastructure security. 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. An Amazon RDS instance is in the private subnet, and an application server is in the public subnet. The security team needs to allow the application server to connect to the RDS instance on port 3306 (MySQL). Which configuration will meet this requirement securely?
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
✓
Add an inbound rule to the RDS security group that allows traffic from the security group of the application server on port 3306.
Option B is correct because it uses a security group reference as the source in the inbound rule for the RDS security group. This allows traffic only from the specific application server(s) associated with that security group, regardless of their IP addresses, and automatically scales if the application server is replaced or scaled. This is the most secure and AWS-recommended method for controlling traffic between resources within a VPC.
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.
- ✗
Add an inbound rule to the RDS security group that allows traffic from the VPC CIDR on port 3306.
Why it's wrong here
This allows traffic from all instances in the VPC, which is too broad.
- ✓
Add an inbound rule to the RDS security group that allows traffic from the security group of the application server on port 3306.
Why this is correct
This restricts access to only the application server's security group.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Add an inbound rule to the RDS security group that allows traffic from the subnet CIDR of the application server on port 3306.
Why it's wrong here
This allows any instance in that subnet, which may include other instances.
- ✗
Add an inbound rule to the RDS security group that allows traffic from 0.0.0.0/0 on port 3306.
Why it's wrong here
This exposes the database to the internet.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse security group references with CIDR-based rules, mistakenly thinking that allowing traffic from the subnet CIDR (Option C) is equivalent to allowing traffic from the application server, when in fact it permits any resource in that subnet to connect.
Detailed technical explanation
How to think about this question
Security group references work by evaluating the network interfaces attached to the source security group; when you reference another security group, AWS automatically resolves the private IP addresses of all instances associated with that group. This is more dynamic than using CIDR blocks because it accommodates auto-scaling, instance replacements, and changes to the application server's IP without requiring rule updates. In contrast, subnet CIDR rules are static and do not differentiate between instances within the same subnet.
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.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this SCS-C02 question test?
Infrastructure Security — This question tests Infrastructure Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add an inbound rule to the RDS security group that allows traffic from the security group of the application server on port 3306. — Option B is correct because it uses a security group reference as the source in the inbound rule for the RDS security group. This allows traffic only from the specific application server(s) associated with that security group, regardless of their IP addresses, and automatically scales if the application server is replaced or scaled. This is the most secure and AWS-recommended method for controlling traffic between resources within a VPC.
What should I do if I get this SCS-C02 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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Last reviewed: Jul 4, 2026
This SCS-C02 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 SCS-C02 exam.
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