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.
Exhibit
VPC: vpc-0a1b2c3d
Private subnets: 10.0.10.0/24, 10.0.11.0/24
Route tables:
10.0.10.0/24 -> 0.0.0.0/0 -> nat-07fabc123
10.0.11.0/24 -> 0.0.0.0/0 -> nat-07fabc123
VPC Flow Logs (sample):
10.0.10.45 -> 52.216.23.11 ACCEPT
10.0.10.45 -> 54.239.28.85 ACCEPT
10.0.11.18 -> 52.94.76.21 ACCEPT
Cost Explorer last 30 days:
NATGateway-Hours: $31.20
NATGateway-Bytes: $614.80
App requirement: no internet access is needed; only AWS service access is required.
Based on the exhibit, your application runs entirely in private subnets and only needs to reach Amazon S3, Amazon DynamoDB, AWS Secrets Manager, and CloudWatch Logs. The monthly bill is dominated by NAT Gateway charges. Which change most directly reduces cost while preserving private connectivity to these AWS services?
VPC: vpc-0a1b2c3d
Private subnets: 10.0.10.0/24, 10.0.11.0/24
Route tables:
10.0.10.0/24 -> 0.0.0.0/0 -> nat-07fabc123
10.0.11.0/24 -> 0.0.0.0/0 -> nat-07fabc123
VPC Flow Logs (sample):
10.0.10.45 -> 52.216.23.11 ACCEPT
10.0.10.45 -> 54.239.28.85 ACCEPT
10.0.11.18 -> 52.94.76.21 ACCEPT
Cost Explorer last 30 days:
NATGateway-Hours: $31.20
NATGateway-Bytes: $614.80
App requirement: no internet access is needed; only AWS service access is required.
A
Replace the NAT Gateway with an Internet Gateway and keep the current private subnet routes unchanged.
Why wrong: An Internet Gateway would expose instances to the public internet unless the design is changed substantially. It does not reduce cost safely for private-only workloads.
B
Add a second NAT Gateway in another Availability Zone to reduce cross-AZ data transfer charges.
Why wrong: A second NAT Gateway can improve availability, but it usually increases fixed hourly cost. It does not solve the core problem of paying for internet egress to AWS services.
C
Create only interface endpoints for all four services and keep the NAT Gateway for fallback.
Why wrong: Interface endpoints are not the cheapest or always the correct choice for S3 and DynamoDB. Keeping the NAT Gateway preserves unnecessary cost and the fallback is not required by the scenario.
D
Create S3 and DynamoDB gateway endpoints, create interface endpoints for Secrets Manager and CloudWatch Logs, update route tables, and remove the NAT Gateway.
S3 and DynamoDB use gateway endpoints, which are the cost-effective private path for those services. Secrets Manager and CloudWatch Logs require interface endpoints for private access. Once these are in place, the NAT Gateway is no longer needed for this workload, eliminating the hourly and per-GB NAT charges while keeping traffic on the AWS network.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create S3 and DynamoDB gateway endpoints, create interface endpoints for Secrets Manager and CloudWatch Logs, update route tables, and remove the NAT Gateway.
Option D is correct because it replaces the costly NATGateway with free VPC Gateway Endpoints for S3 and DynamoDB, and uses AWS PrivateLink interface endpoints for Secrets Manager and CloudWatch Logs. This eliminates all internet-bound data transfer costs while keeping traffic entirely within the AWS network, directly addressing the cost concern without sacrificing private connectivity.
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.
✗
Replace the NAT Gateway with an Internet Gateway and keep the current private subnet routes unchanged.
Why it's wrong here
An Internet Gateway would expose instances to the public internet unless the design is changed substantially. It does not reduce cost safely for private-only workloads.
✗
Add a second NAT Gateway in another Availability Zone to reduce cross-AZ data transfer charges.
Why it's wrong here
A second NATGateway can improve availability, but it usually increases fixed hourly cost. It does not solve the core problem of paying for internet egress to AWS services.
✗
Create only interface endpoints for all four services and keep the NAT Gateway for fallback.
Why it's wrong here
Interface endpoints are not the cheapest or always the correct choice for S3 and DynamoDB. Keeping the NATGateway preserves unnecessary cost and the fallback is not required by the scenario.
✓
Create S3 and DynamoDB gateway endpoints, create interface endpoints for Secrets Manager and CloudWatch Logs, update route tables, and remove the NAT Gateway.
Why this is correct
S3 and DynamoDB use gateway endpoints, which are the cost-effective private path for those services. Secrets Manager and CloudWatch Logs require interface endpoints for private access. Once these are in place, the NAT Gateway is no longer needed for this workload, eliminating the hourly and per-GB NAT charges while keeping traffic on the AWS network.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume all AWS services require the same type of VPC endpoint, leading them to either use only interface endpoints (costly) or keep the NATGateway as a safety net, missing the opportunity to use free gateway endpoints for S3 and DynamoDB.
Trap categories for this question
Scenario analysis trap
Interface endpoints are not the cheapest or always the correct choice for S3 and DynamoDB. Keeping the NAT Gateway preserves unnecessary cost and the fallback is not required by the scenario.
Detailed technical explanation
How to think about this question
VPC Gateway Endpoints for S3 and DynamoDB use prefix lists and route table entries to direct traffic to the AWS service without leaving the VPC network, incurring no hourly or data processing charges. In contrast, interface endpoints (AWS PrivateLink) create elastic network interfaces in the subnet and charge per hour and per GB of data processed, making them cost-effective only for services that don't offer gateway endpoints. A common real-world scenario is a hybrid architecture where workloads in private subnets need to access both S3 (via gateway endpoint) and Secrets Manager (via interface endpoint), and removing the NAT Gateway can reduce monthly costs by hundreds or thousands of dollars depending on data volume.
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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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 S3 and DynamoDB gateway endpoints, create interface endpoints for Secrets Manager and CloudWatch Logs, update route tables, and remove the NAT Gateway. — Option D is correct because it replaces the costly NAT Gateway with free VPC Gateway Endpoints for S3 and DynamoDB, and uses AWS PrivateLink interface endpoints for Secrets Manager and CloudWatch Logs. This eliminates all internet-bound data transfer costs while keeping traffic entirely within the AWS network, directly addressing the cost concern without sacrificing private connectivity.
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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