ANS-C01 Network Design Practice Question
A company has a VPC with public and private subnets. The public subnet has a NAT gateway for outbound internet access from private subnets. The private subnets have EC2 instances that need to access an S3 bucket in the same region. The company wants to minimize data transfer costs and avoid traversing the internet. What is the MOST cost-effective solution?
⚠ Common exam trap
AWS often tests the misconception that interface endpoints are always the best choice for AWS service access, but for S3 and DynamoDB, gateway endpoints are the most cost-effective because they are free and avoid the per-GB data processing charges of interface endpoints.
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
✓
Create a VPC Gateway Endpoint for S3 and attach a policy allowing access from the private subnets.
A VPC Gateway Endpoint for S3 allows private subnet instances to access S3 over the AWS network without traversing the internet or a NAT gateway, eliminating data transfer costs for the NAT gateway and avoiding internet egress charges. This is the most cost-effective solution because gateway endpoints are free and use prefix lists in the route table to direct traffic to S3 via the AWS backbone.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure an S3 bucket policy that restricts access to the VPC's public IP addresses.
Why it's wrong here
Private subnet instances do not have public IPs, and this would not prevent traffic from going through the NAT gateway.
- ✓
Create a VPC Gateway Endpoint for S3 and attach a policy allowing access from the private subnets.
Why this is correct
Gateway endpoints are free and keep traffic within AWS network.
- ✗
Route traffic to the NAT gateway and then to the S3 bucket using a VPC peering connection.
Why it's wrong here
NAT gateway adds cost and traffic goes over the internet, not cost-effective.
- ✗
Create a VPC Interface Endpoint for S3 and associate with the private subnets.
Why it's wrong here
Interface endpoints for S3 incur hourly charges and data processing costs, making them less cost-effective than Gateway endpoints.
Visual reference
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.