The answer is that the Lambda function is not in the same VPC as the RDS instance, or lacks proper routing to reach it. When a Lambda function is configured to access a VPC, it loses default internet connectivity and can only communicate with resources within that VPC unless you add a NAT Gateway or VPC endpoints. A timeout specifically indicates a network connectivity failure, not an authentication or permission issue—access denied errors would occur with wrong IAM roles, and cold starts would cause latency, not a hard timeout. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of Lambda’s VPC networking behavior and the common pitfall of forgetting that VPC-enabled Lambda functions cannot reach RDS databases in a private subnet without a route through a NAT device or a VPC endpoint. A helpful memory tip: “No route, no response—timeout tells you the network is the problem, not the permissions.”
DVA-C02 Security Practice Question
This DVA-C02 practice question tests your understanding of security. 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 writing a Lambda function that needs to access an RDS database. The function currently fails with a timeout. 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 is not in the same VPC as the RDS instance
If the Lambda function is in a VPC without a proper VPC configuration (NATGateway or VPC endpoints), it cannot access the RDS database. Option A is possible but less likely than network issues. Option C (wrong permissions) would cause access denied, not timeout. Option D (cold start) would not cause a timeout to RDS.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 is not in the same VPC as the RDS instance
Why this is correct
Without VPC connectivity, the Lambda function cannot reach the RDS instance, causing a timeout.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The Lambda function has a cold start delay
Why it's wrong here
Cold start adds latency but typically does not cause a timeout.
✗
The RDS instance is not publicly accessible
Why it's wrong here
Even if not public, Lambda in the same VPC can access it.
✗
The Lambda function does not have an IAM role granting RDS access
Why it's wrong here
Missing permissions would result in access denied, not timeout.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DVA-C02 NAT questions on configuration and troubleshooting.
Security — This question tests Security — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The Lambda function is not in the same VPC as the RDS instance — If the Lambda function is in a VPC without a proper VPC configuration (NAT Gateway or VPC endpoints), it cannot access the RDS database. Option A is possible but less likely than network issues. Option C (wrong permissions) would cause access denied, not timeout. Option D (cold start) would not cause a timeout to RDS.
What should I do if I get this DVA-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DVA-C02 NAT questions on configuration and troubleshooting.
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?
Static NAT maps one inside address to one outside address.
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