A NAT (Network Address Translation) gateway is a device that enables instances in a private subnet to connect to the internet or other AWS services. It is commonly used to give an entire private network access to the internet without assigning each host a public IPv4 address. NAT gateways can be public or private, and they map the source private IPv4 address of the instances to the private IPv4 address of the NAT gateway. When sending response traffic to the instances, the NAT gateway translates the address back to the original source IP address.

Some key features of NAT gateways include:

• Bandwidth: A NAT gateway supports 5 Gbps of bandwidth and automatically scales up to 100 Gbps.
• Packet processing: A NAT gateway can process one million packets per second and automatically scales up to ten million packets per second. Beyond this limit, a NAT gateway will drop packets.
• SNAT: NAT gateways provide the SNAT (Source Network Address Translation) feature, which offers additional security protection by preventing external networks from communicating with ECS instances in the VPC unless the ECS instances initiate requests to access external networks.

NAT gateways are available on various cloud platforms, including Amazon Web Services (AWS), Microsoft Azure, and Alibaba Cloud.