What is the function of an AWS NAT Gateway?

The function of an AWS NAT Gateway is primarily to enable internet access for instances in a private subnet. When you deploy resources in a Virtual Private Cloud (VPC), you can configure some subnets to be private, meaning they do not have a direct route to the internet. This is often the case for resources that need to be protected from public internet exposure, such as databases and application servers.

A NAT Gateway allows these private instances to initiate outbound traffic to the internet while still preventing unsolicited inbound traffic from reaching those instances. This is essential for tasks like software updates or accessing external services, as private subnets themselves do not have a public IP address assigned.

For example, if you have an application running on an EC2 instance in a private subnet that needs to download updates from the internet or communicate with external APIs, it can route that traffic through a NAT Gateway located in a public subnet, which has direct internet access. This setup secures the private resources while allowing necessary outbound communication.

In summary, the NAT Gateway serves this critical function of bridging the network traffic between private subnet instances and the internet, enabling secure and controlled internet access without exposing service endpoints.