- A
Launch the RDS instance in the default VPC.
Why wrong: Placing the instance in a different VPC would complicate connectivity.
- B
Change the DB subnet group to include the application server's subnet.
Why wrong: The DB subnet group defines which subnets the RDS instance can be in, not which subnets can connect to it.
- C
Add a network ACL rule allowing inbound traffic on port 5432 from the application server's public IP.
Why wrong: Network ACLs are stateless and the application uses private IP; also security groups are sufficient.
- D
Modify the RDS instance to be publicly accessible.
Why wrong: Public accessibility is not needed if the application is in the same VPC.
- E
Update the security group inbound rule to allow traffic from the application server's private IP address.
The application connects from its private IP within the VPC, so the security group should allow that private IP.
DBS-C01 Database Security Practice Question
This DBS-C01 practice question tests your understanding of database security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 database specialist is troubleshooting a connectivity issue with an Amazon RDS for PostgreSQL instance. The instance is in a VPC with a public subnet. The security group allows inbound traffic on port 5432 from the application server's IP address. The application server is in the same VPC but in a private subnet. Despite the security group configuration, the application cannot connect. Which action should the specialist take to resolve the issue?
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
Update the security group inbound rule to allow traffic from the application server's private IP address.
Option E is correct because the application server is in a private subnet, so it communicates with the RDS instance using its private IP address. The security group inbound rule must allow traffic from the application server's private IP (or the security group of the application server) on port 5432. The current rule only allows the application server's public IP, which is not used for traffic within the VPC, causing the connection failure.
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.
- ✗
Launch the RDS instance in the default VPC.
Why it's wrong here
Placing the instance in a different VPC would complicate connectivity.
- ✗
Change the DB subnet group to include the application server's subnet.
Why it's wrong here
The DB subnet group defines which subnets the RDS instance can be in, not which subnets can connect to it.
- ✗
Add a network ACL rule allowing inbound traffic on port 5432 from the application server's public IP.
Why it's wrong here
Network ACLs are stateless and the application uses private IP; also security groups are sufficient.
- ✗
Modify the RDS instance to be publicly accessible.
Why it's wrong here
Public accessibility is not needed if the application is in the same VPC.
- ✓
Update the security group inbound rule to allow traffic from the application server's private IP address.
Why this is correct
The application connects from its private IP within the VPC, so the security group should allow that private IP.
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 may confuse public and private IP addressing within a VPC, assuming that allowing the application server's public IP in the security group is sufficient, when in fact traffic between instances in the same VPC always uses private IPs.
Detailed technical explanation
How to think about this question
In a VPC, instances in private subnets use private IP addresses for internal communication, even if they have a public IP assigned via a NAT gateway or internet gateway. Security groups are stateful and evaluate inbound rules based on the source IP of the traffic; if the source is a private IP, the rule must reference that private IP or the security group of the source. Network ACLs are stateless and require both inbound and outbound rules, but they are not the primary cause here because the security group is blocking the traffic.
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.
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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: Update the security group inbound rule to allow traffic from the application server's private IP address. — Option E is correct because the application server is in a private subnet, so it communicates with the RDS instance using its private IP address. The security group inbound rule must allow traffic from the application server's private IP (or the security group of the application server) on port 5432. The current rule only allows the application server's public IP, which is not used for traffic within the VPC, causing the connection failure.
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 11, 2026
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