The answer is to set the RDS security group inbound rule to allow traffic from the EC2 security group on port 3306. This is the most secure configuration because it uses a security group reference as the source rather than a CIDR block, which adheres to the principle of least privilege by granting access only to instances associated with that specific EC2 security group. On the AWS Certified Database Specialty DBS-C01 exam, this concept tests your understanding of how to restrict network access to an RDS instance without exposing it to the internet, and a common trap is choosing a CIDR-based rule that might inadvertently allow broader access or require manual updates. Remember that security group references automatically scale with your EC2 fleet, eliminating the need to manage IP ranges. Memory tip: think “SG-to-SG, not IP-to-IP” for the most secure database access.
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 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.
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.
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.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A security audit reveals that an Amazon RDS for MySQL DB instance is accessible from the internet. The security team requires that the database be accessible only from a specific set of application servers within the same VPC. Which solution should be implemented?
easy
✓ A.Modify the DB instance's security group to allow inbound traffic only from the application servers' security group.
B.Apply a network ACL that denies inbound traffic from 0.0.0.0/0 and allows from the application servers' IP range.
C.Enable encryption at rest on the DB instance to prevent unauthorized access.
D.Move the DB instance to a private subnet and configure a bastion host for access.
Why A: Option B is correct because a security group with an inbound rule that references the application servers' security group restricts access to only those instances. Option A is wrong because network ACLs are stateless and block all traffic if not correctly configured, but security groups are more appropriate for instance-level access. Option C is wrong because changing the subnet to private and using a bastion host is unnecessary if the app servers are in the same VPC. Option D is wrong because enabling encryption does not restrict network access.
Variation 2. A company is deploying a new Amazon RDS for MySQL database in a VPC. The database must be accessible only from an application server running in the same VPC. The security team also wants to ensure that the database is not accessible from the internet. Which TWO configurations are required? (Choose TWO.)
easy
A.Place the DB instance in a public subnet.
B.Modify the DB parameter group to restrict network access.
✓ C.Configure the security group to allow inbound traffic only from the application server's security group.
✓ D.Set the DB instance to be not publicly accessible.
E.Configure a network ACL to deny inbound traffic from 0.0.0.0/0.
Why C: Options B and D are correct. Option B: Making the DB instance not publicly accessible ensures it cannot be reached from the internet. Option D: Configuring the security group to allow inbound traffic only from the application server's security group limits access. Option A is wrong because a public subnet does not prevent internet access; it enables it. Option C is wrong because a network ACL is stateless and less specific than security groups. Option E is wrong because the parameter group does not control network access.
Variation 3. A company has an Amazon RDS for MySQL DB instance that is publicly accessible. The security team wants to restrict access to only specific IP addresses. Which configuration should be used?
medium
A.Create a VPC endpoint for RDS and attach a policy that allows only the specific IP addresses.
B.Use an IAM policy with a condition that restricts the source IP address.
✓ C.Configure a security group associated with the RDS instance to allow inbound traffic only from the specific IP addresses.
D.Configure a network ACL to allow inbound traffic from the specific IP addresses.
Why C: Option B is correct because DB security groups (or VPC security groups) can be configured to allow inbound traffic only from specific IP addresses. Option A is wrong because network ACLs are stateless and less granular. Option C is wrong because the RDS instance is publicly accessible, so it has a public endpoint; a VPC endpoint is not needed. Option D is wrong because IAM policies do not restrict network access.
Variation 4. A company has an Amazon RDS for Oracle DB instance that is publicly accessible. They want to restrict access to only a specific CIDR block. Which two actions must be taken together?
medium
✓ A.Modify the VPC security group to allow inbound traffic on the database port from the specific CIDR, and ensure the DB instance is publicly accessible with the correct security group.
B.Modify the DB subnet group to include only subnets from the allowed CIDR.
C.Add a rule to the network ACL to allow inbound traffic from the CIDR.
D.Set the rds.force_ssl parameter to force encrypted connections from the allowed CIDR.
Why A: Option C is correct because the security group must allow inbound from the specific CIDR, and the DB instance must be publicly accessible. Option A is wrong because subnet assignment is not directly for access control. Option B is wrong because NACLs are stateless and not typically used for RDS access control. Option D is wrong because the DB parameter group does not control network access.
Variation 5. Which TWO actions should a company take to secure an Amazon RDS for MySQL database that is accessible from the internet? (Choose two.)
medium
✓ A.Use a security group that restricts inbound traffic to only the required IP addresses.
B.Disable encryption at rest to reduce latency.
C.Use the default VPC with a public subnet and a network ACL that allows all traffic.
D.Launch the DB instance in a public subnet with a public IP address.
✓ E.Place the DB instance in a private subnet without a public IP address.
Why A: Options B and E are correct. Option B: Placing the DB instance in a private subnet with no direct internet access is a fundamental security measure. Option E: Using security groups to restrict inbound traffic to specific IP addresses limits exposure. Option A is wrong because disabling encryption reduces security. Option C is wrong because using a public subnet increases exposure. Option D is wrong because using the default VPC with a public subnet is insecure.
Last reviewed: Jun 24, 2026
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