- A
Place instances in private subnets but use NAT gateways so traffic to S3 and Secrets Manager goes through the internet; restrict security groups to instance-to-instance only.
Why wrong: NAT still routes traffic through the internet path and contradicts the cost and private-connectivity requirement. Restricting instance-to-instance rules does not prevent public service access through NAT.
- B
Add a VPC gateway endpoint for S3 and an interface VPC endpoint for Secrets Manager; keep instances in private subnets and configure security group rules attached to the endpoints to allow inbound traffic only from the application subnets.
Gateway endpoints provide private routing to S3, and interface endpoints provide private access to Secrets Manager without internet traversal. Security group controls on interface endpoints restrict traffic to only the application subnets, meeting segmentation and cost constraints.
- C
Use public subnets with instances that have no security group rules; rely on AWS services to reject unauthorized traffic.
Why wrong: Public subnets plus missing security controls violates baseline security. Relying on AWS service rejection does not provide explicit network segmentation or deterministic access control.
- D
Create an S3 bucket policy that allows requests from the application instances’ private IP addresses and enable public access to Secrets Manager via the default service endpoint.
Why wrong: Bucket policy cannot safely replace network-level private connectivity. Secrets Manager still requires private endpoint configuration or NAT/IGW routing for private subnets; public access contradicts requirements.
Quick Answer
The answer is to add a VPC gateway endpoint for S3 and an interface VPC endpoint for Secrets Manager, keeping instances in private subnets without a NAT gateway. This architecture is correct because gateway endpoints use AWS’s private network to route S3 traffic directly, while interface endpoints use PrivateLink to bring Secrets Manager into the VPC via an elastic network interface—both bypass the public internet entirely. On the SAA-C03 exam, this scenario tests your understanding of when to use gateway versus interface endpoints, with the common trap being to default to a NAT gateway or a single endpoint type for both services. Remember that S3 and DynamoDB are the only services supporting gateway endpoints, while most other AWS services (like Secrets Manager) require interface endpoints. A useful memory tip: “S3 goes through the gateway, everything else interfaces through PrivateLink.”
SAA-C03 Design Secure Architectures Practice Question
This SAA-C03 practice question tests your understanding of design secure 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 an application in private subnets (no inbound internet). The application must access Amazon S3 and AWS Secrets Manager endpoints without routing through the public internet and without exposing the instances to NAT gateways due to cost. Security requirements also state that only the required VPC traffic should be allowed to reach AWS services.
Which architecture best satisfies these requirements?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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
Add a VPC gateway endpoint for S3 and an interface VPC endpoint for Secrets Manager; keep instances in private subnets and configure security group rules attached to the endpoints to allow inbound traffic only from the application subnets.
Option B is correct because it uses a VPC gateway endpoint for S3 and an interface VPC endpoint for Secrets Manager, both of which allow private subnet instances to access these AWS services without traversing the public internet or requiring a NAT gateway. The security group rules attached to the interface endpoint restrict inbound traffic to only the application subnets, satisfying the security requirement of allowing only required VPC traffic. This architecture avoids NAT gateway costs and keeps instances isolated from inbound internet traffic.
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.
- ✗
Place instances in private subnets but use NAT gateways so traffic to S3 and Secrets Manager goes through the internet; restrict security groups to instance-to-instance only.
Why it's wrong here
NAT still routes traffic through the internet path and contradicts the cost and private-connectivity requirement. Restricting instance-to-instance rules does not prevent public service access through NAT.
- ✓
Add a VPC gateway endpoint for S3 and an interface VPC endpoint for Secrets Manager; keep instances in private subnets and configure security group rules attached to the endpoints to allow inbound traffic only from the application subnets.
Why this is correct
Gateway endpoints provide private routing to S3, and interface endpoints provide private access to Secrets Manager without internet traversal. Security group controls on interface endpoints restrict traffic to only the application subnets, meeting segmentation and cost constraints.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use public subnets with instances that have no security group rules; rely on AWS services to reject unauthorized traffic.
Why it's wrong here
Public subnets plus missing security controls violates baseline security. Relying on AWS service rejection does not provide explicit network segmentation or deterministic access control.
- ✗
Create an S3 bucket policy that allows requests from the application instances’ private IP addresses and enable public access to Secrets Manager via the default service endpoint.
Why it's wrong here
Bucket policy cannot safely replace network-level private connectivity. Secrets Manager still requires private endpoint configuration or NAT/IGW routing for private subnets; public access contradicts requirements.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may assume all AWS service endpoints require a NAT gateway or internet gateway for private subnet access, overlooking the cost-effective and secure alternative of VPC endpoints (gateway and interface) that keep traffic within the AWS network.
Detailed technical explanation
How to think about this question
VPC gateway endpoints use AWS PrivateLink to route S3 traffic over the AWS network without leaving the VPC, leveraging prefix lists in the route table. Interface VPC endpoints for Secrets Manager also use PrivateLink, assigning a private IP address from the subnet and allowing security group association to control traffic at the endpoint level. A common subtlety is that gateway endpoints do not support security groups, so access control for S3 relies on bucket policies and route table entries, while interface endpoints support both security groups and network ACLs for granular control.
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.
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
Design Secure Architectures — This question tests Design Secure Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add a VPC gateway endpoint for S3 and an interface VPC endpoint for Secrets Manager; keep instances in private subnets and configure security group rules attached to the endpoints to allow inbound traffic only from the application subnets. — Option B is correct because it uses a VPC gateway endpoint for S3 and an interface VPC endpoint for Secrets Manager, both of which allow private subnet instances to access these AWS services without traversing the public internet or requiring a NAT gateway. The security group rules attached to the interface endpoint restrict inbound traffic to only the application subnets, satisfying the security requirement of allowing only required VPC traffic. This architecture avoids NAT gateway costs and keeps instances isolated from inbound internet traffic.
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.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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 company runs an application in private subnets (no inbound internet). The application must access Amazon S3 and AWS Secrets Manager endpoints without routing through the public internet and without exposing the instances to NAT gateways due to cost. Security requirements also state that only the required VPC traffic should be allowed to reach AWS services. Which architecture best satisfies these requirements?
medium- A.Place instances in private subnets but use NAT gateways so traffic to S3 and Secrets Manager goes through the internet; restrict security groups to instance-to-instance only.
- ✓ B.Add a VPC gateway endpoint for S3 and an interface VPC endpoint for Secrets Manager; keep instances in private subnets and configure security group rules attached to the endpoints to allow inbound traffic only from the application subnets.
- C.Use public subnets with instances that have no security group rules; rely on AWS services to reject unauthorized traffic.
- D.Create an S3 bucket policy that allows requests from the application instances’ private IP addresses and enable public access to Secrets Manager via the default service endpoint.
Why B: Option B is correct because it uses a VPC gateway endpoint for Amazon S3 and an interface VPC endpoint for AWS Secrets Manager, both of which allow private subnet instances to access these services without traversing the public internet or requiring a NAT gateway. The security group rules attached to the interface endpoint restrict inbound traffic to only the application subnets, satisfying the security requirement of allowing only required VPC traffic. This architecture meets all constraints: no public internet, no NAT gateway cost, and least-privilege access.
Last reviewed: Jun 11, 2026
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