- A
The NAT Gateway is not configured with a route to the internet.
Why wrong: The scenario states a NAT Gateway exists; lack of a route would cause a different failure, but the timeout at exactly the function timeout suggests a connection block rather than routing issue.
- B
The Lambda function's security group does not allow outbound traffic.
Correct. If the security group's outbound rules do not permit HTTPS traffic, the connection cannot be established, resulting in a timeout. This is the most common cause in such scenarios.
- C
The external API's response time exceeds 30 seconds.
Why wrong: If the API response time were the issue, the function would likely hang until the timeout, but the function should have a sensible timeout. The pattern of exactly 30 seconds indicates the function timeout is being reached, not the API delay.
- D
The Lambda function's VPC does not have an internet gateway.
Why wrong: In this scenario, the VPC has a NAT Gateway which requires an Internet Gateway. An Internet Gateway is present; the issue is not the IGW.
Quick Answer
The answer is a missing security group egress rule for outbound traffic. This is the most likely cause because when a Lambda function runs inside a VPC, it loses default internet access and must route traffic through a NAT Gateway or NAT instance. Even with that routing correctly configured, the function’s security group acts as a stateful firewall—if it lacks an outbound rule allowing HTTPS on port 443, the packets are silently dropped, causing the function to hang until its 30-second timeout expires. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding that VPC-enabled Lambda requires both a proper route to a NAT and explicit security group egress rules; a common trap is assuming the NAT alone is sufficient. Remember the mnemonic: “No egress, no progress”—if the security group doesn’t allow traffic out, the Lambda can’t reach the internet, no matter how good the route is.
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 troubleshooting an AWS Lambda function that returns timeout errors when calling an external HTTPS API. The function is configured with a 30-second timeout and runs in a VPC with a public subnet and NAT Gateway. The developer checks CloudWatch logs and sees that the function is timing out at exactly 30 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 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 Lambda function's security group does not allow outbound traffic.
Option B is correct because Lambda functions running in a VPC do not automatically get internet access; they require a route to a NAT Gateway or NAT instance. Even with a NAT Gateway, the Lambda function's security group must allow outbound traffic (e.g., HTTPS on port 443) to reach the external API. Without this rule, outbound packets are dropped, causing the function to hang until the configured timeout (30 seconds) expires, resulting in a timeout error.
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 NAT Gateway is not configured with a route to the internet.
- ✓
The Lambda function's security group does not allow outbound traffic.
Why this is correct
Correct. If the security group's outbound rules do not permit HTTPS traffic, the connection cannot be established, resulting in a timeout. This is the most common cause in such scenarios.
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 external API's response time exceeds 30 seconds.
Why it's wrong here
If the API response time were the issue, the function would likely hang until the timeout, but the function should have a sensible timeout. The pattern of exactly 30 seconds indicates the function timeout is being reached, not the API delay.
- ✗
The Lambda function's VPC does not have an internet gateway.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a NAT Gateway alone provides internet access to Lambda, overlooking that security group egress rules must explicitly allow outbound traffic to the destination.
Trap categories for this question
Scenario analysis trap
The scenario states a NAT Gateway exists; lack of a route would cause a different failure, but the timeout at exactly the function timeout suggests a connection block rather than routing issue.
Detailed technical explanation
How to think about this question
Lambda functions in a VPC use Elastic Network Interfaces (ENIs) with security groups that default to denying all outbound traffic unless explicitly allowed. The function's timeout at exactly 30 seconds indicates a network-level hang rather than a slow API response, as TCP connection attempts fail silently when outbound traffic is blocked. In practice, developers often forget to add an outbound rule for HTTPS (port 443) to the security group, leading to this exact symptom—timeout at the configured limit.
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 DVA-C02 question test?
Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The Lambda function's security group does not allow outbound traffic. — Option B is correct because Lambda functions running in a VPC do not automatically get internet access; they require a route to a NAT Gateway or NAT instance. Even with a NAT Gateway, the Lambda function's security group must allow outbound traffic (e.g., HTTPS on port 443) to reach the external API. Without this rule, outbound packets are dropped, causing the function to hang until the configured timeout (30 seconds) expires, resulting in a timeout error.
What should I do if I get this DVA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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Last reviewed: Jun 11, 2026
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