- A
Create an interface VPC endpoint for STS (com.amazonaws.<region>.sts) and associate it with the instance subnets and a security group that allows HTTPS.
Interface endpoints provide private, in-VPC connectivity to AWS APIs like STS without requiring internet access or NAT.
- B
Create a gateway VPC endpoint for S3 and route the STS traffic through the S3 endpoint gateway.
Why wrong: Gateway endpoints are for specific services (like S3/DynamoDB) and cannot be used to route STS traffic to the correct API.
- C
Open an inbound rule in the instances’ security group to allow outbound HTTPS to the internet CIDR block directly.
Why wrong: Security groups control allowed traffic, but the subnet route table still needs a path. Without NAT/endpoint routing, traffic cannot reach STS.
- D
Attach an Internet Gateway to the private subnet route table so the STS API can be reached over public internet.
Why wrong: Adding an Internet Gateway to private subnets contradicts the requirement to keep instances private and increases exposure.
SAA-C03 Interface VPC Endpoints use AWS PrivateLink. Practice Question
This SAA-C03 practice question tests your understanding of design secure architectures. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: interface VPC Endpoints use AWS PrivateLink.. 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.
Your EC2 instances run in private subnets with no NAT gateway. The instances use the AWS SDK to call STS AssumeRole to obtain temporary credentials for other services. Application logs show errors like: "EndpointConnectionError: Could not connect to https://sts.<region>.amazonaws.com".
Which change most directly resolves this while keeping instances private?
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 an interface VPC endpoint for STS (com.amazonaws.<region>.sts) and associate it with the instance subnets and a security group that allows HTTPS.
The error indicates the EC2 instances cannot reach the STS public endpoint over the internet because they are in private subnets without a NAT gateway. An interface VPC endpoint for STS (com.amazonaws.<region>.sts) allows private, direct connectivity to the STS API using AWS PrivateLink, without requiring internet access. Associating the endpoint with the instance subnets and a security group that allows HTTPS (port 443) resolves the connectivity issue while keeping the instances private.
Key principle: Interface VPC Endpoints use AWS PrivateLink.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Create an interface VPC endpoint for STS (com.amazonaws.<region>.sts) and associate it with the instance subnets and a security group that allows HTTPS.
Why this is correct
Interface endpoints provide private, in-VPC connectivity to AWS APIs like STS without requiring internet access or NAT.
Related concept
Interface VPC Endpoints use AWS PrivateLink.
- ✗
Create a gateway VPC endpoint for S3 and route the STS traffic through the S3 endpoint gateway.
Why it's wrong here
Gateway endpoints are for specific services (like S3/DynamoDB) and cannot be used to route STS traffic to the correct API.
- ✗
Open an inbound rule in the instances’ security group to allow outbound HTTPS to the internet CIDR block directly.
Why it's wrong here
Security groups control allowed traffic, but the subnet route table still needs a path. Without NAT/endpoint routing, traffic cannot reach STS.
- ✗
Attach an Internet Gateway to the private subnet route table so the STS API can be reached over public internet.
Why it's wrong here
Adding an Internet Gateway to private subnets contradicts the requirement to keep instances private and increases exposure.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse gateway endpoints (which only work for S3 and DynamoDB) with interface endpoints (which work for many services like STS), or they mistakenly think security group rules alone can enable outbound internet access without a route.
Detailed technical explanation
How to think about this question
Interface VPC endpoints use AWS PrivateLink to create an elastic network interface (ENI) in the subnet with a private IP address, enabling traffic to STS to stay within the AWS network. The security group attached to the endpoint controls inbound and outbound traffic; for STS, you need an outbound rule allowing HTTPS to the endpoint's private IP or the VPC CIDR, and an inbound rule allowing HTTPS from the instances. This approach also avoids data transfer costs associated with NAT gateways and improves security by eliminating internet exposure.
KKey Concepts to Remember
- Interface VPC Endpoints use AWS PrivateLink.
- They provide private connectivity to AWS services via ENIs.
- STS is a service that supports interface VPC endpoints.
- Traffic to an interface endpoint remains within the AWS network.
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
Interface VPC Endpoints use AWS PrivateLink.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
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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 — Interface VPC Endpoints use AWS PrivateLink..
What is the correct answer to this question?
The correct answer is: Create an interface VPC endpoint for STS (com.amazonaws.<region>.sts) and associate it with the instance subnets and a security group that allows HTTPS. — The error indicates the EC2 instances cannot reach the STS public endpoint over the internet because they are in private subnets without a NAT gateway. An interface VPC endpoint for STS (com.amazonaws.<region>.sts) allows private, direct connectivity to the STS API using AWS PrivateLink, without requiring internet access. Associating the endpoint with the instance subnets and a security group that allows HTTPS (port 443) resolves the connectivity issue while keeping the instances private.
What should I do if I get this SAA-C03 question wrong?
Review interface VPC Endpoints use AWS PrivateLink., then practise related SAA-C03 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Interface VPC Endpoints use AWS PrivateLink.
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Last reviewed: Jun 11, 2026
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