- A
Keep the NAT gateway and reduce instance size to lower NAT throughput charges
Why wrong: Reducing instance size might reduce some traffic, but it does not directly eliminate NAT gateway usage. NAT costs can remain high if the application still sends requests through NAT.
- B
Create a Gateway VPC endpoint for S3 and an Interface VPC endpoint for Secrets Manager, then route requests via those endpoints instead of NAT
VPC endpoints allow private connectivity to specific AWS services without sending traffic through a NAT gateway. S3 uses a Gateway endpoint type, while Secrets Manager uses an Interface endpoint type. This directly targets and reduces NAT gateway costs while meeting the “no internet egress” requirement.
- C
Switch Secrets Manager to use S3 as a storage backend so both services can use the S3 endpoint only
Why wrong: Secrets Manager is a managed secrets service and does not provide an option to “swap” storage to S3 for direct endpoint sharing. This would change the application and introduces unnecessary redesign risk.
- D
Move the private subnets to public subnets and attach an Internet Gateway to eliminate NAT
Why wrong: Using public subnets with an Internet Gateway removes NAT, but it allows internet-routed traffic, which violates the requirement to avoid internet egress and can increase exposure.
SAA-C03 Design Cost-Optimized Architectures Practice Question
This SAA-C03 practice question tests your understanding of design cost-optimized architectures. 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 hosts application servers in private subnets. They must access Amazon S3 and read secrets from AWS Secrets Manager, but they want to avoid internet egress. They currently use a NAT gateway and see high NAT-related costs. What change most directly reduces cost while keeping traffic on the AWS network?
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 Gateway VPC endpoint for S3 and an Interface VPC endpoint for Secrets Manager, then route requests via those endpoints instead of NAT
Option B is correct because it replaces the NAT gateway with VPC endpoints, which are free of data processing charges and keep all traffic within the AWS network. A Gateway VPC endpoint for S3 uses prefix lists and route table entries to send S3 traffic directly over the AWS backbone, while an Interface VPC endpoint for Secrets Manager uses AWS PrivateLink to provide private connectivity without internet egress. This eliminates NAT gateway hourly and data processing costs, directly addressing the cost concern.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Keep the NAT gateway and reduce instance size to lower NAT throughput charges
- ✓
Create a Gateway VPC endpoint for S3 and an Interface VPC endpoint for Secrets Manager, then route requests via those endpoints instead of NAT
Why this is correct
VPC endpoints allow private connectivity to specific AWS services without sending traffic through a NAT gateway. S3 uses a Gateway endpoint type, while Secrets Manager uses an Interface endpoint type. This directly targets and reduces NAT gateway costs while meeting the “no internet egress” requirement.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Switch Secrets Manager to use S3 as a storage backend so both services can use the S3 endpoint only
Why it's wrong here
Secrets Manager is a managed secrets service and does not provide an option to “swap” storage to S3 for direct endpoint sharing. This would change the application and introduces unnecessary redesign risk.
- ✗
Move the private subnets to public subnets and attach an Internet Gateway to eliminate NAT
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think NAT gateway costs can be reduced by scaling down instances, or that Secrets Manager can be accessed via an S3 endpoint, when in fact VPC endpoints are the only way to eliminate NAT costs while keeping traffic private and on the AWS network.
Detailed technical explanation
How to think about this question
Gateway VPC endpoints for S3 use route table entries with a prefix list for the S3 service (e.g., com.amazonaws.region.s3) to direct traffic over the AWS global network without traversing the internet or a NAT device. Interface VPC endpoints for Secrets Manager use AWS PrivateLink, which creates an elastic network interface in the subnet with a private IP address, leveraging AWS Direct Connect or VPN for on-premises connectivity if needed. In real-world scenarios, this architecture is critical for compliance with regulations like PCI DSS that require no internet egress for sensitive data access.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
Design Cost-Optimized Architectures — This question tests Design Cost-Optimized Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create a Gateway VPC endpoint for S3 and an Interface VPC endpoint for Secrets Manager, then route requests via those endpoints instead of NAT — Option B is correct because it replaces the NAT gateway with VPC endpoints, which are free of data processing charges and keep all traffic within the AWS network. A Gateway VPC endpoint for S3 uses prefix lists and route table entries to send S3 traffic directly over the AWS backbone, while an Interface VPC endpoint for Secrets Manager uses AWS PrivateLink to provide private connectivity without internet egress. This eliminates NAT gateway hourly and data processing costs, directly addressing the cost concern.
What should I do if I get this SAA-C03 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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