DBS-C01 Monitoring and Troubleshooting Practice Question
An application running on Amazon EC2 is unable to connect to an Amazon RDS for SQL Server DB instance. The security group for the RDS instance allows inbound traffic from the security group of the EC2 instance on port 1433. The network ACLs allow all traffic. What is a likely cause of the connectivity 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
✓
The RDS instance is in a private subnet and does not have a public IP address
If the RDS instance is in a private subnet without a public IP address, the EC2 instance cannot connect using the public DNS endpoint unless the EC2 is in the same VPC. Since the security group and network ACLs are correctly configured, the most likely cause is that the RDS instance is not publicly accessible and the EC2 instance is attempting to connect from outside the VPC or via the public endpoint. Option B is wrong because network ACLs allow all traffic. Option C is wrong because the security group inbound rule is correctly configured to allow traffic from the EC2 security group on port 1433. Option D is wrong because port 1433 is the default SQL Server port, and if it were not, the error message would indicate a timeout, not a connectivity issue.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The RDS instance is in a private subnet and does not have a public IP address
Why this is correct
Without a public IP, the EC2 instance cannot reach it over the internet.
- ✗
The network ACL is blocking the traffic
Why it's wrong here
Network ACLs allow all traffic.
- ✗
The security group inbound rule is incorrectly configured
Why it's wrong here
The security group allows traffic from the EC2 security group.
- ✗
The database port is not 1433
Why it's wrong here
SQL Server default port is 1433.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DBS-C01 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 DBS-C01 exam.