The answer is a routing issue: the EC2 instance is sending S3 traffic over the internet instead of through the VPC endpoint. This happens because when an S3 bucket policy explicitly grants access only to a specific VPC endpoint, the request must physically traverse that endpoint to be valid. If the EC2 instance has a public IP address and its route table directs S3 traffic (via the S3 prefix list) to an internet gateway rather than the endpoint, the request arrives at S3 from the public internet, not the endpoint, and is denied. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of how VPC endpoints interact with resource-based policies—a common trap is assuming that being in the same VPC is sufficient. Remember the key distinction: the endpoint is the identity, not the VPC. Memory tip: “Endpoint, not environment—traffic must flow through the door, not the wall.”
DVA-C02 Troubleshooting and Optimization Practice Question
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 company uses an S3 bucket to store sensitive documents. The bucket policy allows access only from a specific VPC endpoint. However, a developer in the same VPC is unable to access the bucket from an EC2 instance. 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 EC2 instance is routing traffic to S3 through the internet instead of the VPC endpoint.
S3 bucket policies that restrict access to a specific VPC endpoint require that requests originate from that endpoint. The EC2 instance must route S3 traffic through the VPC endpoint. If the instance has a public IP and routes directly to S3, the request won't go through the endpoint.
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 EC2 instance is routing traffic to S3 through the internet instead of the VPC endpoint.
Why this is correct
If traffic goes through the internet, the source IP won't match the VPC endpoint, causing denial.
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 S3 bucket policy requires encryption in transit, which is not configured.
Why it's wrong here
Encryption in transit is not the issue; the error would be different.
✗
The VPC endpoint policy does not grant access to the developer's IAM role.
Why it's wrong here
The endpoint policy might be missing permissions, but the bucket policy is the primary restriction.
✗
The EC2 instance does not have an IAM role assigned.
Why it's wrong here
IAM role is needed for permissions, but the bucket policy restricts access via endpoint, not IAM.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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.
Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The EC2 instance is routing traffic to S3 through the internet instead of the VPC endpoint. — S3 bucket policies that restrict access to a specific VPC endpoint require that requests originate from that endpoint. The EC2 instance must route S3 traffic through the VPC endpoint. If the instance has a public IP and routes directly to S3, the request won't go through the endpoint.
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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