SAA-C03 Design Secure Architectures Practice Question
A company hosts an internal HTTP API on an internal Network Load Balancer (NLB) in VPC A. A partner team in a separate AWS account needs access, but their VPC CIDR overlaps with VPC A, so VPC peering is not feasible.
Security requirements state the API must remain non-public (no internet-facing ALB/NLB) and access must use AWS private networking.
Which architecture best meets these requirements?
⚠ Common exam trap
Test-takers frequently assume VPC peering can handle overlapping CIDRs with route table adjustments, but AWS explicitly prohibits overlapping CIDRs in VPC peering connections, making PrivateLink the only viable private networking option.
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
✓
Use AWS PrivateLink by creating a VPC endpoint service backed by the NLB in VPC A, then create an interface VPC endpoint in the partner VPC with appropriate endpoint access controls.
AWS PrivateLink allows you to expose an internal NLB in VPC A as a VPC endpoint service, and the partner team can create an interface VPC endpoint in their own VPC to connect privately. This solution avoids overlapping CIDR issues because traffic flows through PrivateLink’s network interfaces using private IPs, not through VPC peering or internet routing. It also satisfies the non-public requirement since the API remains accessible only via private networking within AWS.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Use AWS PrivateLink by creating a VPC endpoint service backed by the NLB in VPC A, then create an interface VPC endpoint in the partner VPC with appropriate endpoint access controls.
Why this is correct
PrivateLink exposes the service privately via interface endpoints, avoiding peering and keeping the NLB non-public for secure partner access.
- ✗
Expose the NLB to the internet with an Elastic IP and restrict access using the NLB’s security group only.
Why it's wrong here
Making the NLB internet-facing violates non-public requirements, even if security groups limit allowed sources.
When this WOULD be correct
This option would be correct if the question allowed a public-facing API and required high availability with static IP addresses, such as for a customer-facing application that needs to whitelist IPs in a firewall, and there was no restriction on internet exposure.
- ✗
Use VPC peering between VPC A and the partner VPC and update route tables to resolve the overlap.
Why it's wrong here
VPC peering cannot handle overlapping CIDRs, and route-table changes cannot resolve IP address overlap safely.
When this WOULD be correct
This option would be correct if the VPCs had non-overlapping CIDR blocks and the requirement was to connect two VPCs privately without using a VPN or AWS Transit Gateway, and the API was accessible via an internal NLB or ALB.
- ✗
Deploy a NAT gateway in VPC A and route the partner’s traffic to the NLB through the NAT gateway.
Why it's wrong here
NAT gateways enable outbound internet egress for instances, not private, deterministic access to internal load balancers across accounts.
When this WOULD be correct
If the requirement were for a private subnet in VPC A to access the internet (e.g., download patches) while remaining non-public, a NAT gateway in a public subnet would be correct. The question would specify outbound internet access from a private subnet.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The SAA-C03 exam frequently reuses these exact scenarios with slightly different constraints.
✓Use AWS PrivateLink by creating a VPC endpoint service backed by the NLB in VPC A, then create an interface VPC endpoint in the partner VPC with appropriate endpoint access controls.Correct answer▾
Why this is correct
PrivateLink exposes the service privately via interface endpoints, avoiding peering and keeping the NLB non-public for secure partner access.
✗Expose the NLB to the internet with an Elastic IP and restrict access using the NLB’s security group only.Wrong answer — click to see why▾
Why this is wrong here
The NLB cannot be made internet-facing with an Elastic IP because the requirement explicitly states the API must remain non-public and use AWS private networking. Additionally, NLB security groups are not supported; security is managed via subnet ACLs and target group health checks.
★ When this WOULD be the correct answer
This option would be correct if the question allowed a public-facing API and required high availability with static IP addresses, such as for a customer-facing application that needs to whitelist IPs in a firewall, and there was no restriction on internet exposure.
Why candidates choose this
Candidates may think adding an Elastic IP to the NLB is a simple way to make it reachable from another account, overlooking the non-public requirement and the fact that NLB security groups are not supported.
✗Use VPC peering between VPC A and the partner VPC and update route tables to resolve the overlap.Wrong answer — click to see why▾
Why this is wrong here
VPC peering cannot resolve overlapping CIDR blocks; overlapping IP ranges make routing impossible, and the requirement for non-public access is already met by peering, but the overlap is the blocker.
★ When this WOULD be the correct answer
This option would be correct if the VPCs had non-overlapping CIDR blocks and the requirement was to connect two VPCs privately without using a VPN or AWS Transit Gateway, and the API was accessible via an internal NLB or ALB.
Why candidates choose this
Candidates may think VPC peering is the simplest private connectivity method and overlook the CIDR overlap constraint, or assume overlapping ranges can be handled with route table adjustments.
✗Deploy a NAT gateway in VPC A and route the partner’s traffic to the NLB through the NAT gateway.Wrong answer — click to see why▾
Why this is wrong here
A NAT gateway is used for outbound internet access from private subnets, not for inbound traffic from another VPC. It cannot route traffic from a partner VPC to an internal NLB, and it does not resolve VPC CIDR overlap issues.
★ When this WOULD be the correct answer
If the requirement were for a private subnet in VPC A to access the internet (e.g., download patches) while remaining non-public, a NAT gateway in a public subnet would be correct. The question would specify outbound internet access from a private subnet.
Why candidates choose this
Candidates may confuse NAT gateway with a solution for cross-VPC connectivity, thinking it can forward inbound traffic, or they may mistakenly believe it can handle overlapping CIDRs by translating addresses.
Analysis generated from the official SAA-C03blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SAA-C03 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SAA-C03 exam.