SAA-C03 Interface VPC Endpoints use AWS PrivateLink. Practice Question
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?
⚠ Common exam trap
Many candidates 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.
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.
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.
- ✗
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.
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JA
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.