AWS Certified Advanced Networking Specialty Practice Exam

The NAT gateway should be placed in a public subnet to provide Internet access for instances in a private subnet. This is because a NAT gateway is specifically designed to allow instances that do not have their own public IP addresses (i.e., instances in a private subnet) to access the Internet for purposes such as downloading updates or accessing external services.

When the NAT gateway is in a public subnet, it can have a public IP address and can communicate directly with the Internet. The private subnet instances, which do not have public IP addresses, route their outbound traffic through the NAT gateway. This setup ensures that while the instances in the private subnet maintain their privacy and security (since they are not directly accessible from the Internet), they can still initiate outbound connections.

This architecture leverages the NAT gateway's ability to manage the translation of private IP addresses to a public IP address, allowing for smooth communication with the outside world while maintaining proper security and isolation within the private subnet.