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Question 776 of 1,040

Design Cost-Optimized Architectures →easyMultiple ChoiceObjective-mapped

Quick Answer

The correct answer is to remove the NAT Gateway path for S3 and DynamoDB by creating Gateway VPC endpoints for both services and updating the private subnet route tables to direct that traffic to the endpoints. This works because Gateway VPC endpoints allow EC2 instances in private subnets to reach S3 and DynamoDB over the AWS backbone network without ever leaving the VPC, completely bypassing the NAT Gateway and eliminating its data processing charges for that traffic. On the SAA-C03 exam, this scenario tests your understanding of when to use Gateway endpoints versus Interface endpoints—a common trap is assuming you need a NAT Gateway for all AWS service access, but S3 and DynamoDB are the only two services that support Gateway endpoints, making them the most cost-effective choice for private subnet access. Remember the memory tip: “Gateway for S3 and DDB—no NAT fee, just AWS.”

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 runs Amazon EC2 instances in private subnets. Those instances only need to access Amazon S3 (read/write) and Amazon DynamoDB. The VPC currently routes all outbound traffic through a NAT Gateway, increasing monthly cost. What change most directly reduces NAT Gateway usage for these AWS services?

Question 1easymultiple choice

Read the full NAT/PAT explanation →

A
Remove the NAT Gateway path for S3 and DynamoDB by creating S3 Gateway VPC endpoints and DynamoDB Gateway VPC endpoints, and updating the private subnet route tables to route S3/DynamoDB traffic to those endpoints.
S3 and DynamoDB Gateway VPC endpoints keep traffic inside AWS without sending it to the internet, so requests don’t traverse the NAT Gateway (avoiding NAT hourly charges and per-GB NAT data processing).
B
Keep the NAT Gateway but disable any cross-region routing settings for the route table entries that point to the NAT Gateway.
Why wrong: Cross-region routing settings do not prevent the traffic from still being sent to the NAT Gateway. If the route still points to NAT, NAT charges still apply.
C
Create interface VPC endpoints for all services (including S3) and route S3 traffic to the interface endpoint network interfaces (ENIs).
Why wrong: S3 does not use interface VPC endpoints. S3 uses Gateway VPC endpoints (and requires appropriate prefix-list route entries). Using the wrong endpoint type won’t address the NAT path.
D
Add an IAM policy that denies requests unless they originate from the public subnet, so the application sends fewer requests through the NAT Gateway.
Why wrong: IAM does not control whether traffic traverses the NAT Gateway at the network layer. Even if requests are denied, the EC2 instances will still attempt outbound connectivity through the existing NAT routes (and you would also likely break the application).

Full breakdown with real-world context →

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

✓

Remove the NAT Gateway path for S3 and DynamoDB by creating S3 Gateway VPC endpoints and DynamoDB Gateway VPC endpoints, and updating the private subnet route tables to route S3/DynamoDB traffic to those endpoints.

Option A is correct because S3 Gateway VPC endpoints and DynamoDB Gateway VPC endpoints allow EC2 instances in private subnets to access these services directly over the AWS network without traversing a NAT Gateway. This eliminates NAT Gateway data processing charges for S3 and DynamoDB traffic, directly reducing costs. The route tables in the private subnets are updated to direct S3 and DynamoDB traffic to the gateway endpoints, bypassing the NAT Gateway entirely.

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.

✓
Remove the NAT Gateway path for S3 and DynamoDB by creating S3 Gateway VPC endpoints and DynamoDB Gateway VPC endpoints, and updating the private subnet route tables to route S3/DynamoDB traffic to those endpoints.
Why this is correct
S3 and DynamoDB Gateway VPC endpoints keep traffic inside AWS without sending it to the internet, so requests don’t traverse the NAT Gateway (avoiding NAT hourly charges and per-GB NAT data processing).
Related concept
Read the scenario before looking for a memorised answer.
✗
Keep the NAT Gateway but disable any cross-region routing settings for the route table entries that point to the NAT Gateway.
Why it's wrong here
Cross-region routing settings do not prevent the traffic from still being sent to the NAT Gateway. If the route still points to NAT, NAT charges still apply.
✗
Create interface VPC endpoints for all services (including S3) and route S3 traffic to the interface endpoint network interfaces (ENIs).
Why it's wrong here
S3 does not use interface VPC endpoints. S3 uses Gateway VPC endpoints (and requires appropriate prefix-list route entries). Using the wrong endpoint type won’t address the NAT path.
✗
Add an IAM policy that denies requests unless they originate from the public subnet, so the application sends fewer requests through the NAT Gateway.
Why it's wrong here
IAM does not control whether traffic traverses the NAT Gateway at the network layer. Even if requests are denied, the EC2 instances will still attempt outbound connectivity through the existing NAT routes (and you would also likely break the application).

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates may confuse gateway endpoints with interface endpoints, assuming all AWS services require interface endpoints, or they may overlook that DynamoDB also supports gateway endpoints, leading them to choose the more expensive interface endpoint option for S3.

Detailed technical explanation

How to think about this question

S3 Gateway VPC endpoints use prefix lists and route table entries to direct traffic to S3 via the AWS global network, avoiding internet gateways or NAT devices. DynamoDB Gateway VPC endpoints similarly use route table entries to access DynamoDB without internet routing. Under the hood, gateway endpoints are horizontally scaled, redundant, and highly available by default, with no additional cost for the endpoint itself—only standard data transfer charges apply, which are typically lower than NAT Gateway data processing fees.

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: Remove the NAT Gateway path for S3 and DynamoDB by creating S3 Gateway VPC endpoints and DynamoDB Gateway VPC endpoints, and updating the private subnet route tables to route S3/DynamoDB traffic to those endpoints. — Option A is correct because S3 Gateway VPC endpoints and DynamoDB Gateway VPC endpoints allow EC2 instances in private subnets to access these services directly over the AWS network without traversing a NAT Gateway. This eliminates NAT Gateway data processing charges for S3 and DynamoDB traffic, directly reducing costs. The route tables in the private subnets are updated to direct S3 and DynamoDB traffic to the gateway endpoints, bypassing the NAT Gateway entirely.

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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Same concept, more angles

1 more ways this is tested on SAA-C03

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A service in private subnets downloads product images from Amazon S3 and stores job state in DynamoDB. A NAT Gateway is currently the only route to AWS services, and the monthly bill is dominated by NAT data processing charges. Which two changes will most directly reduce that cost? Select two.

medium

✓ A.Create a gateway VPC endpoint for Amazon S3.
✓ B.Create a gateway VPC endpoint for Amazon DynamoDB.
C.Add an internet gateway and move the instances into public subnets.
D.Replace the NAT Gateway with a Site-to-Site VPN connection.
E.Create an interface endpoint for S3 instead of a gateway endpoint.

Why A: A is correct because a gateway VPC endpoint for Amazon S3 allows instances in private subnets to access S3 directly over the AWS network without traversing the internet or a NAT Gateway. This eliminates NAT data processing charges for S3 traffic, which is the dominant cost driver in this scenario.

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