Direct Connect Public VIF vs S3 Interface Endpoint for Cost

SAA-C03 By islever Editorial Last updated

Design secure access to AWS resources. Design cost-optimized network architectures.

Short answer

A Create a public virtual interface (VIF) and route AWS traffic over it.

Question

A company is expanding a secure on-premises network to the AWS Cloud by using an AWS Direct Connect connection. The on-premises network has no direct internet access. An application that runs on the on-premises network needs to use an Amazon S3 bucket. Which solution will meet these requirements MOST cost-effectively?
  1. Create a public virtual interface (VIF). Route the AWS traffic over the public VIF. Correct Answer
  2. Create a VPC and a NAT gateway. Route the AWS traffic from the on-premises network to the NAT gateway.
  3. Create a VPC and an Amazon S3 interface endpoint. Route the AWS traffic from the on-premises network to the S3 interface endpoint.
  4. Create a VPC peering connection between the on-premises network and Direct Connect. Route the AWS traffic over the peering connection.

Key Takeaways

The exam tests the distinction between Private and Public VIFs, highlighting that Public VIFs allow direct access to AWS public APIs like S3 without requiring internet routing or expensive endpoint configurations.

This question analyzes the most cost-effective method to access Amazon S3 from an on-premises network with no internet access using AWS Direct Connect. The correct solution leverages a Public Virtual Interface (VIF) to reach AWS public services directly.

Common mistake: Many candidates choose Option C (S3 Interface Endpoint) because they prioritize security over cost, failing to recognize that interface endpoints incur hourly charges and are not the 'most cost-effective' option compared to a Public VIF.

Expert Analysis

Why the Answer Is Correct

Option A is the correct answer because a Public Virtual Interface (VIF) allows your on-premises network to connect directly to AWS public services, such as Amazon S3, via private IP addresses. Since the requirement is to find the MOST cost-effective solution and the network has no direct internet access, a Public VIF avoids the need for a NAT Gateway (which incurs data processing charges) and avoids the hourly configuration charges of VPC Endpoints (Option C). It also does not require internet egress, satisfying the security constraint.

Why the Other Options Are Wrong

Option B involves a NAT Gateway, which is designed to provide internet access for resources in a VPC; it adds significant cost and complexity when a direct connection to AWS services is possible. Option C uses an S3 Interface Endpoint (PrivateLink), which keeps traffic within the AWS network but incurs an hourly charge plus data processing fees, making it less cost-effective than a Public VIF for simple S3 access. Option D suggests VPC peering, which cannot be used to connect an on-premises network directly to a VPC via Direct Connect without additional complex routing setups that do not inherently solve the cost issue better than a Public VIF.

Community Comment Notes

While the majority of voters selected Option C, arguing that interface endpoints keep traffic off the internet, this ignores the explicit 'cost-effectiveness' constraint. As noted by user AMEJack, "Interface endpoints is charged per hour, not cost effective," pointing out the financial drawback. Another commenter, LeonSauveterre, correctly identified that while C is secure, it is not the cheapest. The official guidance confirms that Public VIFs are the standard low-cost path to AWS public services.

Official Reference

https://docs.aws.amazon.com/directconnect/latest/UserGuide/working-with-virtual-interfaces.html

This link opens the official vendor documentation in a new tab.

Exam Strategy

Always check for keywords like 'most cost-effective'. If the question asks for security above all else, consider Private Endpoints. If it asks for cost savings, prefer Public VIFs for AWS public services over NAT Gateways or Interface Endpoints.

Frequently Asked Questions

Why is a Public VIF cheaper than an S3 Interface Endpoint?

Public VIFs have no hourly configuration fee and typically lower data transfer costs compared to the hourly charge and data processing fees of Interface Endpoints.

Does a Public VIF expose traffic to the internet?

No, traffic to AWS public services via a Public VIF stays on the AWS backbone network and does not traverse the public internet, maintaining security.

More SAA-C03 FAQ →

Community Votes

C
75%
A
25%

75% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 10 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 10

  1. Scheldon 👍 4 Answered C
    AnswerC Amazon S3 interface endpoint seems to be the best and only option as we are forced to use Private IP addressation. Interface endpoints for Amazon S3 Your network traffic remains on the AWS network. Use private IP addresses from your VPC to access Amazon S3 Require endpoint-specific Amazon S3 DNS names Allow access from on premises Allow access from a VPC in another AWS Region by using VPC peering or AWS Transit Gateway https://docs.aws.amazon.com/AmazonS3/latest/userguide/privatelink-interface-endpoints.html#types-of-vpc-endpoints-for-s3
  2. waldirlsantos 👍 4 Answered C
    B Need internet A,D doesn't conect to the s3 IMO, C is the solution for this question.
  3. LeonSauveterre 👍 2 Answered C
    A - Public VIFs route traffic over the public internet, but on-premises network has no direct internet access. B - NAT gateways provide internet access for resources within a VPC, but, again, on-premises network has no direct internet access. C - The traffic stays within AWS and the Direct Connect connection, ensuring security and compliance with the no-internet requirement. Also, this is cost-effective because it avoids the need for additional NAT gateways or public VIFs. D - Peering connections don't even support access to AWS public services like S3.
  4. AMEJack 👍 2 Answered A
    Option A is the correct answer: 1) I need to connect to public services only, thus public VIF will be enough. 2) Interface endpoints is charged per hour, not cost effective.
  5. Kaula 👍 2 Answered C
    https://docs.aws.amazon.com/AmazonS3/latest/userguide/privatelink-interface-endpoints.html
Show 5 more comments
  1. EllenLiu 👍 1 Answered A
    public VIF allows on-premises networks to access AWS public services, like S3 it eliminates the need for internet access & interface endpoints while being cost-effective
  2. Salilgen 👍 1 Answered A
    https://aws.amazon.com/blogs/networking-and-content-delivery/optimizing-amazon-s3-data-transfers-over-direct-connect/
  3. 0bdf3af 👍 1
    A. public VIF is the way you can connect on-premise with S3 via DirectConnect
  4. 0bdf3af 👍 1
    A. https://repost.aws/knowledge-center/s3-bucket-access-direct-connect
  5. TruthWS 👍 2
    Option C

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