- A
Deploy a NAT Gateway in each public subnet and add a default route in the private subnet route tables pointing to the NAT Gateway.
NAT Gateway provides outbound-only internet access securely.
- B
Create a VPC endpoint for the external API service.
Why wrong: VPC endpoints only work for AWS services.
- C
Assign public IP addresses to the EC2 instances and allow outbound traffic in the security group.
Why wrong: Public IPs expose instances to inbound traffic.
- D
Set up a VPN connection to an on-premises network that has internet access.
Why wrong: Overly complex and not directly needed.
Question 1,050 of 1,705
NAT Gateway for Private Subnet Outbound Internet Access
This ANS-C01 practice question tests your understanding of network implementation. 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 has deployed a VPC with a public subnet and a private subnet in each of two Availability Zones. They have an Application Load Balancer (ALB) in the public subnets and EC2 instances in the private subnets. The EC2 instances need to access an external API over HTTPS. What is the MOST secure way to provide this access?
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
✓
Deploy a NAT Gateway in each public subnet and add a default route in the private subnet route tables pointing to the NAT Gateway.
A NAT Gateway in each public subnet provides a managed, highly available path for EC2 instances in private subnets to initiate outbound HTTPS connections to the internet while preventing inbound connections from reaching them. Adding a default route (0.0.0.0/0) in the private subnet route tables pointing to the NAT Gateway ensures traffic destined for the external API is forwarded through the NAT Gateway, which performs source network address translation (SNAT) using its Elastic IP. This is the most secure method because it avoids exposing the EC2 instances directly to the internet and leverages AWS-managed infrastructure for scalability and fault tolerance.
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.
- ✓
Deploy a NAT Gateway in each public subnet and add a default route in the private subnet route tables pointing to the NAT Gateway.
- ✗
Create a VPC endpoint for the external API service.
Why it's wrong here
VPC endpoints only work for AWS services.
- ✗
Assign public IP addresses to the EC2 instances and allow outbound traffic in the security group.
Why it's wrong here
Public IPs expose instances to inbound traffic.
- ✗
Set up a VPN connection to an on-premises network that has internet access.
Why it's wrong here
Overly complex and not directly needed.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse VPC endpoints (PrivateLink) with NAT Gateways, assuming a VPC endpoint can be used for any external API, but VPC endpoints only work for services that explicitly support AWS PrivateLink or are AWS services, not arbitrary public HTTPS APIs.
Detailed technical explanation
How to think about this question
A NAT Gateway operates at Layer 3/4, translating private source IPs (from the RFC 1918 range) to its Elastic IP for outbound traffic, and it maintains connection state so that return traffic is correctly forwarded back to the originating instance. Unlike a NAT instance, a NAT Gateway is fully managed by AWS, automatically scales up to 45 Gbps, and does not require patching or instance management. In a multi-AZ deployment, deploying a NAT Gateway in each public subnet ensures that if one AZ fails, instances in the other AZ can still reach the internet via their local NAT Gateway, avoiding cross-AZ data transfer costs and single points of failure.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Deploy a NAT Gateway in each public subnet and add a default route in the private subnet route tables pointing to the NAT Gateway. — A NAT Gateway in each public subnet provides a managed, highly available path for EC2 instances in private subnets to initiate outbound HTTPS connections to the internet while preventing inbound connections from reaching them. Adding a default route (0.0.0.0/0) in the private subnet route tables pointing to the NAT Gateway ensures traffic destined for the external API is forwarded through the NAT Gateway, which performs source network address translation (SNAT) using its Elastic IP. This is the most secure method because it avoids exposing the EC2 instances directly to the internet and leverages AWS-managed infrastructure for scalability and fault tolerance.
What should I do if I get this ANS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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
5 more ways this is tested on ANS-C01
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 has deployed a VPC with public and private subnets. The private subnets need outbound internet access for software updates. Which service should be used to provide this access without exposing the instances to inbound traffic?
easy- A.Attach an Internet Gateway to the VPC and add a default route to it from the private subnets.
- B.Set up a VPN connection to an on-premises network that has internet access.
- C.Use a Direct Connect connection to route traffic through an on-premises internet gateway.
- ✓ D.Deploy a NAT Gateway in a public subnet and add a default route to it from the private subnets.
Why D: A NAT Gateway, deployed in a public subnet with an Elastic IP, allows instances in private subnets to initiate outbound traffic to the internet (e.g., for software updates) while preventing any unsolicited inbound connections from the internet. The private subnet’s route table directs default traffic (0.0.0.0/0) to the NAT Gateway, which performs source network address translation (SNAT) to the gateway’s Elastic IP, enabling outbound-only access.
Variation 2. A company is deploying a fleet of EC2 instances in private subnets. The instances need to download patches from the internet. The company wants to minimize cost and avoid managing NAT instances. The VPC has an internet gateway (IGW) attached. What should the company do?
medium- A.Attach the IGW to the private subnet route table.
- ✓ B.Deploy a NAT Gateway in a public subnet and update the private subnet route tables.
- C.Create a VPC endpoint for internet access.
- D.Launch a NAT instance and configure routing.
Why B: A NAT Gateway, deployed in a public subnet with an Elastic IP, allows instances in private subnets to initiate outbound traffic to the internet (e.g., for patch downloads) while preventing inbound connections from the internet. This solution is fully managed by AWS, eliminating the need to manage a NAT instance, and it is cost-effective compared to maintaining a dedicated instance. The private subnet route table must have a default route (0.0.0.0/0) pointing to the NAT Gateway ID.
Variation 3. A company is deploying a VPC with public and private subnets. The private subnets need outbound internet access for updates, but must not be directly reachable from the internet. Which AWS service should be used to achieve this?
easy- A.AWS Site-to-Site VPN
- B.AWS Direct Connect
- C.Internet Gateway
- ✓ D.NAT Gateway
Why D: A NAT Gateway enables instances in private subnets to initiate outbound IPv4 traffic to the internet (e.g., for software updates) while preventing unsolicited inbound connections from the internet. It translates the private source IP to the NAT Gateway's Elastic IP address, so responses return to the gateway, which then forwards them to the private instance. This meets the requirement of outbound-only internet access without direct internet reachability.
Variation 4. A company is deploying a VPC with public and private subnets. They want to allow instances in a private subnet to access the internet for software updates while preventing inbound internet traffic. Which configuration should be used?
easy- A.Create a VPC endpoint for internet access
- B.Use a transit gateway with a NAT instance
- C.Attach an internet gateway to the VPC and add a route in the private subnet to the internet gateway for 0.0.0.0/0
- ✓ D.Attach an internet gateway to the VPC, and create a NAT gateway in a public subnet. Add a route in the private subnet route table to the NAT gateway for 0.0.0.0/0
Why D: Option D is correct because a NAT gateway, deployed in a public subnet with an Internet Gateway (IGW) attached, allows instances in private subnets to initiate outbound IPv4 traffic to the internet (e.g., for software updates) while the IGW's one-way translation prevents unsolicited inbound traffic from reaching the private instances. The private subnet's route table must include a default route (0.0.0.0/0) pointing to the NAT gateway's elastic network interface.
Variation 5. A company is designing a VPC with public and private subnets. They want EC2 instances in private subnets to be able to access the internet for software updates. Which AWS service should they use?
easy- A.AWS Direct Connect
- B.Internet Gateway (IGW)
- C.VPC Peering connection
- ✓ D.NAT Gateway
Why D: A NAT Gateway enables EC2 instances in private subnets to initiate outbound traffic to the internet (e.g., for software updates) while preventing the internet from initiating inbound connections to those instances. It translates the private IP addresses of the instances to the NAT Gateway's Elastic IP address using source network address translation (SNAT), allowing them to reach public endpoints.
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Last reviewed: Jul 4, 2026
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