NAT Gateway provides SNAT, DNAT, and bandwidth sharing functions.
NAT Gateway supports SNAT, allowing ECS instances without a public IP address in a VPC to access the Internet.
In addition, SNAT can operate as a simple firewall that protects backend ECS instances. An external terminal can access an ECS instance after the ECS instance actively establishes a connection with the external terminal. An untrustworthy external terminal cannot access a backend ECS instance if no connection is established.
NAT Gateway supports DNAT and maps a public IP address to a private IP address. Then, the ECS instance with the public IP address can provide public service.
DNAT supports both port mapping and IP mapping.
You can associate an NAT Gateway with an EIP and add the EIP to Internet Shared Bandwidth. After an EIP is added to an Internet Shared Bandwidth, the original billing method of the EIP loses effect, and only the instance fee of the EIP is charged.