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Question 323 of 1,040

Design Secure Architectures →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is to create a Gateway VPC Endpoint for S3 and associate it with the private subnet route tables. This is correct because EC2 instances in private subnets without a NAT Gateway have no route to the internet, so any HTTPS requests to S3 time out. A Gateway VPC Endpoint allows traffic to reach S3 over the AWS internal network without requiring internet access, and the missing piece is the route table association that directs S3-bound traffic to the endpoint. On the SAA-C03 exam, this scenario tests your understanding of how Gateway Endpoints differ from Interface Endpoints—S3 and DynamoDB both support Gateway Endpoints, but the trap here is that DynamoDB can also use a Gateway Endpoint, yet the question specifically isolates S3 as failing. A common memory tip is “S3 and DynamoDB are the only two services that use Gateway Endpoints; if you see a private subnet with no NAT, think Gateway, not Interface.”

SAA-C03 Design Secure Architectures 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: gateway VPC endpoints are for S3 and DynamoDB only.. 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.

An application runs on EC2 instances in private subnets in a VPC. There is no NAT gateway. The instances need to download objects from S3 over HTTPS and also call DynamoDB. The security group outbound rules allow TCP 443 to the VPC endpoint addresses. After deployment, the app times out when connecting to S3, but it can reach DynamoDB. Which single change is most likely to restore S3 connectivity?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

Question 1mediummultiple choice

Read the full NAT/PAT explanation →

A
Create a Gateway VPC endpoint for S3 and associate it with the private subnet route tables that contain the instances.
S3 connectivity without NAT typically requires a Gateway VPC endpoint. For a gateway endpoint, you must update the route tables to direct S3 traffic to the endpoint. If DynamoDB works but S3 times out, it often means DynamoDB has the required endpoint while S3 is missing or not routed via the correct route tables.
B
Replace the security group egress rule to allow all outbound traffic to 0.0.0.0/0 on TCP 443.
Why wrong: Allowing 0.0.0.0/0 does not create a route to the S3 service without NAT. Security groups do not override routing; if traffic is not routed through the S3 VPC endpoint, the connection will still time out.
C
Add an Internet Gateway to the VPC and route the private subnet’s 0.0.0.0/0 to the IGW.
Why wrong: Adding an Internet Gateway and public routing would defeat the purpose of using private subnets without NAT and increases exposure. The correct solution is service-specific private connectivity using a VPC endpoint for S3.
D
Switch from network ACLs to security groups by removing the existing NACL allow rules for ephemeral ports.
Why wrong: If DynamoDB works, NACL rules are likely not the blocker for outbound traffic in general. Also, the primary requirement for reaching S3 without NAT is routing via the S3 endpoint. NACL changes would be unnecessary if endpoint routing is already correct.

Full breakdown with real-world context →

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 a Gateway VPC endpoint for S3 and associate it with the private subnet route tables that contain the instances.

The application runs in private subnets without a NAT Gateway, so it cannot reach the internet. A Gateway VPC Endpoint for S3 allows private subnet instances to access S3 over the AWS network without internet connectivity. The security group already permits outbound TCP 443 to the endpoint addresses, so the missing piece is the route table association that directs S3 traffic to the endpoint.

Key principle: Gateway VPC endpoints are for S3 and DynamoDB only.

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 a Gateway VPC endpoint for S3 and associate it with the private subnet route tables that contain the instances.
Why this is correct
S3 connectivity without NAT typically requires a Gateway VPC endpoint. For a gateway endpoint, you must update the route tables to direct S3 traffic to the endpoint. If DynamoDB works but S3 times out, it often means DynamoDB has the required endpoint while S3 is missing or not routed via the correct route tables.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Gateway VPC endpoints are for S3 and DynamoDB only.
✗
Replace the security group egress rule to allow all outbound traffic to 0.0.0.0/0 on TCP 443.
Why it's wrong here
Allowing 0.0.0.0/0 does not create a route to the S3 service without NAT. Security groups do not override routing; if traffic is not routed through the S3 VPC endpoint, the connection will still time out.
✗
Add an Internet Gateway to the VPC and route the private subnet’s 0.0.0.0/0 to the IGW.
Why it's wrong here
Adding an Internet Gateway and public routing would defeat the purpose of using private subnets without NAT and increases exposure. The correct solution is service-specific private connectivity using a VPC endpoint for S3.
✗
Switch from network ACLs to security groups by removing the existing NACL allow rules for ephemeral ports.
Why it's wrong here
If DynamoDB works, NACL rules are likely not the blocker for outbound traffic in general. Also, the primary requirement for reaching S3 without NAT is routing via the S3 endpoint. NACL changes would be unnecessary if endpoint routing is already correct.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often assume a security group egress rule to 0.0.0.0/0 is sufficient, forgetting that private subnets without a NAT Gateway have no internet path, so the traffic is silently dropped.

Detailed technical explanation

How to think about this question

Gateway VPC Endpoints use route table entries to direct traffic to S3 via a prefix list, avoiding the public internet. Unlike Interface Endpoints (which use ENIs and private IPs), Gateway Endpoints are free and automatically scale. The security group egress rule to the endpoint addresses works because the endpoint resolves to the VPC’s prefix list, and the route table entry ensures packets are sent to the endpoint’s infrastructure rather than the internet.

KKey Concepts to Remember

Gateway VPC endpoints are for S3 and DynamoDB only.
Gateway endpoints require route table modifications to direct traffic.
Traffic to Gateway endpoints stays within the AWS network.
Security groups allow traffic, but do not provide routing.

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

Gateway VPC endpoints are for S3 and DynamoDB only.

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

Got this wrong? Here's your next step.

Review gateway VPC endpoints are for S3 and DynamoDB only., then practise related SAA-C03 questions on the same topic to reinforce the concept.

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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 — Gateway VPC endpoints are for S3 and DynamoDB only..

What is the correct answer to this question?

The correct answer is: Create a Gateway VPC endpoint for S3 and associate it with the private subnet route tables that contain the instances. — The application runs in private subnets without a NAT Gateway, so it cannot reach the internet. A Gateway VPC Endpoint for S3 allows private subnet instances to access S3 over the AWS network without internet connectivity. The security group already permits outbound TCP 443 to the endpoint addresses, so the missing piece is the route table association that directs S3 traffic to the endpoint.

What should I do if I get this SAA-C03 question wrong?

Review gateway VPC endpoints are for S3 and DynamoDB only., then practise related SAA-C03 questions on the same topic to reinforce the concept.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Gateway VPC endpoints are for S3 and DynamoDB only.

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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. An application runs on EC2 instances in private subnets in a VPC. There is no NAT gateway. The instances need to download objects from S3 over HTTPS and also call DynamoDB. The security group outbound rules allow TCP 443 to the VPC endpoint addresses. After deployment, the app times out when connecting to S3, but it can reach DynamoDB. Which single change is most likely to restore S3 connectivity?

medium

✓ A.Create a Gateway VPC endpoint for S3 and associate it with the private subnet route tables that contain the instances.
B.Replace the security group egress rule to allow all outbound traffic to 0.0.0.0/0 on TCP 443.
C.Add an Internet Gateway to the VPC and route the private subnet’s 0.0.0.0/0 to the IGW.
D.Switch from network ACLs to security groups by removing the existing NACL allow rules for ephemeral ports.

Why A: The application is in private subnets without a NAT Gateway, so it cannot reach the internet. A Gateway VPC Endpoint for S3 allows private subnet instances to access S3 over the AWS network without internet connectivity. The security group already allows TCP 443 to the VPC endpoint addresses, so the missing piece is the route table association that directs S3 traffic to the endpoint.

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