- A
The security group on the EC2 instance blocks outbound traffic to DynamoDB.
Why wrong: Gateway endpoints do not use security groups.
- B
The IAM role does not include the dynamodb:PutItem action.
Why wrong: IAM role is correct.
- C
The route table does not have a route to the DynamoDB prefix list.
Why wrong: Route is present.
- D
The VPC does not have DNS resolution enabled, or the endpoint's private DNS option is disabled.
Correct: Without private DNS, the public endpoint is used, which routes over the internet.
Question 139 of 1,705
ANS-C01 VPC Gateway Endpoint Practice Question
This ANS-C01 practice question tests your understanding of network design. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: vPC Gateway Endpoint. 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 has a VPC with a public subnet and a private subnet. An EC2 instance in the private subnet needs to access an Amazon DynamoDB table. The company wants to avoid sending traffic over the internet. A VPC gateway endpoint for DynamoDB is created and attached to the route table of the private subnet. The EC2 instance has an IAM role that grants access to DynamoDB. However, the application running on the instance cannot connect to DynamoDB. The network team confirms that the route table has a route to the DynamoDB prefix list. 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 VPC does not have DNS resolution enabled, or the endpoint's private DNS option is disabled.
Option D is correct because a VPC gateway endpoint for DynamoDB requires DNS resolution to resolve DynamoDB public hostnames to private IP addresses within the VPC. If DNS resolution is disabled in the VPC, the EC2 instance will resolve DynamoDB endpoints to public IPs, causing traffic to attempt internet routing rather than using the gateway endpoint. Note that gateway endpoints do not have a 'private DNS' option—that is for interface endpoints. The essential requirement is that the VPC's DNS resolution attribute (enableDnsSupport) is enabled.
Key principle: VPC Gateway Endpoint
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 security group on the EC2 instance blocks outbound traffic to DynamoDB.
Why it's wrong here
Gateway endpoints do not use security groups.
- ✗
The IAM role does not include the dynamodb:PutItem action.
Why it's wrong here
IAM role is correct.
- ✗
The route table does not have a route to the DynamoDB prefix list.
Why it's wrong here
Route is present.
- ✓
The VPC does not have DNS resolution enabled, or the endpoint's private DNS option is disabled.
Common exam traps
Common exam trap: answer the scenario, not the keyword
AWS often tests the misconception that a route to the prefix list alone is sufficient for gateway endpoint connectivity, ignoring the critical requirement for DNS resolution to redirect traffic through the endpoint. Do not confuse the 'private DNS' setting of interface endpoints with the DNS resolution requirement for gateway endpoints.
Detailed technical explanation
How to think about this question
VPC gateway endpoints use AWS-managed prefix lists to route traffic via the endpoint's private IPs, but the instance must resolve DynamoDB DNS names (e.g., dynamodb.us-east-1.amazonaws.com) to those private IPs. If the endpoint's private DNS option is disabled, the instance will resolve to public IPs, and traffic will attempt to egress via an internet gateway or NAT device, failing if no such path exists. In real-world scenarios, this often occurs when the VPC's 'Enable DNS resolution' attribute is set to false, or when the endpoint is created without selecting 'Enable Private DNS Name'.
KKey Concepts to Remember
- VPC Gateway Endpoint
- Prefix List
- DNS Resolution
- DynamoDB
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
VPC Gateway Endpoint
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review vPC Gateway Endpoint, then practise related ANS-C01 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Design — This question tests Network Design — VPC Gateway Endpoint.
What is the correct answer to this question?
The correct answer is: The VPC does not have DNS resolution enabled, or the endpoint's private DNS option is disabled. — Option D is correct because a VPC gateway endpoint for DynamoDB requires DNS resolution to resolve DynamoDB public hostnames to private IP addresses within the VPC. If DNS resolution is disabled in the VPC, the EC2 instance will resolve DynamoDB endpoints to public IPs, causing traffic to attempt internet routing rather than using the gateway endpoint. Note that gateway endpoints do not have a 'private DNS' option—that is for interface endpoints. The essential requirement is that the VPC's DNS resolution attribute (enableDnsSupport) is enabled.
What should I do if I get this ANS-C01 question wrong?
Review vPC Gateway Endpoint, then practise related ANS-C01 questions on the same topic to reinforce the concept.
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?
VPC Gateway Endpoint
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Last reviewed: Jun 30, 2026
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