This CV0-004 practice question tests your understanding of troubleshooting. 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.
Exhibit
CloudWatch Logs:
2025-03-01T10:00:00Z ERROR: Connection refused to database endpoint: db.example.com:3306
2025-03-01T10:00:01Z INFO: Retrying in 1 second...
2025-03-01T10:00:02Z ERROR: Connection refused to database endpoint: db.example.com:3306
Refer to the exhibit. An application running on an EC2 instance is failing to connect to an RDS database. What is the most likely issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
CloudWatch Logs:
2025-03-01T10:00:00Z ERROR: Connection refused to database endpoint: db.example.com:3306
2025-03-01T10:00:01Z INFO: Retrying in 1 second...
2025-03-01T10:00:02Z ERROR: Connection refused to database endpoint: db.example.com:3306
A
The database instance is in a different VPC
Why wrong: Cross-VPC connectivity issues typically result in timeout, not connection refused.
B
The security group for the RDS instance does not allow inbound traffic from the EC2 instance
A security group denying inbound traffic causes a TCP reset, resulting in connection refused.
C
The database instance is stopped
Why wrong: A stopped database would not respond at all, leading to a timeout.
D
The application is using the wrong database port
Why wrong: Wrong port would also cause connection refused, but 3306 is correct for MySQL; other ports would show similar error but this is less likely.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The security group for the RDS instance does not allow inbound traffic from the EC2 instance
Option B is correct because a 'connection refused' error typically indicates that the database is reachable but the port is blocked, likely by a security group. Option A is wrong if the database is in a different VPC, the error would be timeout or no route. Option C is wrong because a stopped database would result in a 'no route to host' or timeout. Option D is wrong because port 3306 is standard for MySQL and the error is not about wrong port.
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.
✗
The database instance is in a different VPC
Why it's wrong here
Cross-VPC connectivity issues typically result in timeout, not connection refused.
✓
The security group for the RDS instance does not allow inbound traffic from the EC2 instance
Why this is correct
A security group denying inbound traffic causes a TCP reset, resulting in connection refused.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The database instance is stopped
Why it's wrong here
A stopped database would not respond at all, leading to a timeout.
✗
The application is using the wrong database port
Why it's wrong here
Wrong port would also cause connection refused, but 3306 is correct for MySQL; other ports would show similar error but this is less likely.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Trap categories for this question
Similar concept trap
Wrong port would also cause connection refused, but 3306 is correct for MySQL; other ports would show similar error but this is less likely.
Command / output trap
Wrong port would also cause connection refused, but 3306 is correct for MySQL; other ports would show similar error but this is less likely.
Detailed technical explanation
How to think about this question
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.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 practitioner preparing for the CV0-004 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which CV0-004 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.
Troubleshooting — This question tests Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The security group for the RDS instance does not allow inbound traffic from the EC2 instance — Option B is correct because a 'connection refused' error typically indicates that the database is reachable but the port is blocked, likely by a security group. Option A is wrong if the database is in a different VPC, the error would be timeout or no route. Option C is wrong because a stopped database would result in a 'no route to host' or timeout. Option D is wrong because port 3306 is standard for MySQL and the error is not about wrong port.
What should I do if I get this CV0-004 question wrong?
Identify which CV0-004 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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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