- A
Set the RDS security group inbound rule to allow traffic from the VPC CIDR on port 3306.
Why wrong: This allows all resources in the VPC, too broad.
- B
Set the RDS security group inbound rule to allow traffic from 0.0.0.0/0 on port 3306.
Why wrong: This exposes the database to the internet.
- C
Set the RDS security group inbound rule to allow traffic from the private subnet CIDR on port 3306.
Why wrong: This allows all resources in the subnet, not just EC2.
- D
Set the RDS security group inbound rule to allow traffic from the EC2 security group on port 3306.
This is the most secure, least-privilege approach.
Question 1,676 of 1,730
DBS-C01 Database Security Practice Question
This DBS-C01 practice question tests your understanding of database 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 security engineer is designing a VPC with an RDS instance. The database must not be accessible from the internet, but EC2 instances in a private subnet must connect. Which security group configuration is MOST secure?
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
✓
Set the RDS security group inbound rule to allow traffic from the EC2 security group on port 3306.
Option D is the most secure because it uses a security group reference instead of a CIDR block. By referencing the EC2 security group as the source in the RDS security group inbound rule, only instances associated with that specific security group can communicate with the database on port 3306. This approach adheres to the principle of least privilege and automatically scales as instances are added or removed from the EC2 security group, without needing to update CIDR ranges.
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.
- ✗
Set the RDS security group inbound rule to allow traffic from the VPC CIDR on port 3306.
Why it's wrong here
This allows all resources in the VPC, too broad.
- ✗
Set the RDS security group inbound rule to allow traffic from 0.0.0.0/0 on port 3306.
Why it's wrong here
This exposes the database to the internet.
- ✗
Set the RDS security group inbound rule to allow traffic from the private subnet CIDR on port 3306.
Why it's wrong here
This allows all resources in the subnet, not just EC2.
- ✓
Set the RDS security group inbound rule to allow traffic from the EC2 security group on port 3306.
Why this is correct
This is the most secure, least-privilege approach.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose a CIDR-based rule (like the private subnet CIDR) thinking it is sufficiently restrictive, but they overlook the superior security and operational benefits of using a security group reference, which is a key concept tested in the DBS-C01 exam for database security.
Detailed technical explanation
How to think about this question
Security group rules using a security group ID as the source leverage the AWS hypervisor's stateful firewall to evaluate traffic based on the source instance's security group membership, not its IP address. This means that even if an EC2 instance's private IP changes (e.g., after stop/start), the rule remains valid. In contrast, CIDR-based rules require manual updates if the subnet topology changes, and they cannot distinguish between legitimate database clients and other services running in 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
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this DBS-C01 question test?
Database Security — This question tests Database Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Set the RDS security group inbound rule to allow traffic from the EC2 security group on port 3306. — Option D is the most secure because it uses a security group reference instead of a CIDR block. By referencing the EC2 security group as the source in the RDS security group inbound rule, only instances associated with that specific security group can communicate with the database on port 3306. This approach adheres to the principle of least privilege and automatically scales as instances are added or removed from the EC2 security group, without needing to update CIDR ranges.
What should I do if I get this DBS-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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Last reviewed: Jun 24, 2026
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