Quick Answer
The correct first action is to check the inbound rules of the security group for port 3306. When troubleshooting an RDS MySQL connection from an EC2 instance in the same VPC, the most common cause of failure is that the security group attached to the RDS instance does not explicitly allow inbound traffic on port 3306 from the EC2 instance’s security group. Even if the endpoint is correct and the DB instance is available, the VPC security group acts as a virtual firewall; without a proper inbound rule permitting MySQL traffic, the connection will be silently dropped. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of network-level access controls, a frequent trap where candidates overlook security group rules and instead focus on encryption or instance status. Remember the mnemonic “SG before DB” — always verify security group inbound rules for the correct port before diving into more complex diagnostics.
This DBS-C01 practice question tests your understanding of management and operations. 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 DBA runs the above AWS CLI command. The DB instance is an Amazon RDS for MySQL instance. The DBA needs to connect to the database from an EC2 instance in the same VPC but cannot connect. Which action should be taken first?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Verify that the DB instance endpoint resolves correctly from the EC2 instance.
Why wrong: The endpoint appears correct.
Check the inbound rules of the security group for port 3306.
Security group inbound rules control access to the DB instance.
Enable encryption on the DB instance.
Why wrong: Encryption is not required for connectivity.
Check the DB instance status in the output.
Why wrong: The status is 'available'.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Check the inbound rules of the security group for port 3306.
Option D is correct because the VPC security group (sg-0123456789abcdef0) must allow inbound traffic on port 3306 (MySQL) from the EC2 instance's security group. Option A is wrong because the endpoint is correct. Option B is wrong because the instance is available. Option C is wrong because encryption does not affect connectivity.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Verify that the DB instance endpoint resolves correctly from the EC2 instance.
Why it's wrong here
The endpoint appears correct.
Check the inbound rules of the security group for port 3306.
Why this is correct
Security group inbound rules control access to the DB instance.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Enable encryption on the DB instance.
Why it's wrong here
Encryption is not required for connectivity.
Check the DB instance status in the output.
Why it's wrong here
The status is 'available'.
Common exam traps
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Identify which DBS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Management and Operations — study guide chapter
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FAQ
Management and Operations — This question tests Management and Operations — Read the scenario before looking for a memorised answer..
The correct answer is: Check the inbound rules of the security group for port 3306. — Option D is correct because the VPC security group (sg-0123456789abcdef0) must allow inbound traffic on port 3306 (MySQL) from the EC2 instance's security group. Option A is wrong because the endpoint is correct. Option B is wrong because the instance is available. Option C is wrong because encryption does not affect connectivity.
Identify which DBS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 20, 2026
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.
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