VPC with Public and Private Subnets (NAT)
The configuration for this scenario includes a virtual private cloud (VPC) with a public subnet and a private subnet. We recommend this scenario if you want to run a public-facing web application, while maintaining back-end servers that aren't publicly accessible. A common example is a multi-tier website, with the web servers in a public subnet and the database servers in a private subnet. You can set up security and routing so that the web servers can communicate with the database servers.
The instances in the public subnet can receive inbound traffic directly from the Internet, whereas the instances in the private subnet can't. The instances in the public subnet can send outbound traffic directly to the Internet, whereas the instances in the private subnet can't. Instead, the instances in the private subnet can access the Internet by using a network address translation (NAT) gateway that resides in the public subnet. The database servers can connect to the Internet for software updates using the NAT gateway, but the Internet cannot initiate connections to the database servers.
You can also use the VPC wizard to configure a VPC with a NAT instance; however, we recommend that you use a NAT gateway. For more information, see NAT Gateways.