DVA-C02 Troubleshooting and Optimization Practice Question
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. 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 developer is using AWS Lambda with a VPC configuration. The function needs to access an Amazon RDS instance in the same VPC. The function is timing out after 3 seconds. What is the MOST likely cause?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Lambda function's security group does not allow outbound traffic to the RDS instance.
Option C is correct because Lambda functions in a VPC need a NATgateway or VPC endpoints to access the internet, but to access RDS in the same VPC, they need a route to the RDS subnet. However, the most common cause of timeout is missing a route to the RDS subnet via a VPC peering or transit gateway, but here the RDS is in the same VPC, so the issue is likely that the Lambda function's security group does not allow outbound traffic to the RDS security group. Option A is wrong because RDS proxy is not required. Option B is wrong because the function can access the database directly via its private IP. Option D is wrong because the function timeout is set to 3 seconds, which is the default; it could be increased, but the root cause is connectivity.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 Lambda function's execution role does not have rds:Connect permission.
Why it's wrong here
Database access is controlled by database credentials, not IAM (unless using IAM authentication).
✓
The Lambda function's security group does not allow outbound traffic to the RDS instance.
Why this is correct
The Lambda function's security group must allow outbound traffic to the RDS security group on the database port.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The Lambda function does not have an RDS proxy configured.
Why it's wrong here
RDS proxy is optional and not required for connectivity.
✗
The Lambda function timeout is set too low.
Why it's wrong here
While increasing timeout might help, it would not fix the underlying connectivity issue.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DVA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The Lambda function's security group does not allow outbound traffic to the RDS instance. — Option C is correct because Lambda functions in a VPC need a NAT gateway or VPC endpoints to access the internet, but to access RDS in the same VPC, they need a route to the RDS subnet. However, the most common cause of timeout is missing a route to the RDS subnet via a VPC peering or transit gateway, but here the RDS is in the same VPC, so the issue is likely that the Lambda function's security group does not allow outbound traffic to the RDS security group. Option A is wrong because RDS proxy is not required. Option B is wrong because the function can access the database directly via its private IP. Option D is wrong because the function timeout is set to 3 seconds, which is the default; it could be increased, but the root cause is connectivity.
What should I do if I get this DVA-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DVA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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