NAT Gateway is suitable for the scenarios where ECS instances of the VPC network need to access Internet or to provide public services.
Scenarios 1: set up a high-available SNAT gateway.
In a system, there are some ECS instances need to access Internet but prevent Internet from initiating a connection to these instances. In such cases, you can use the SNAT function of NAT Gateway to set up an SNAT gateway.
Scenarios 2: provide public services
The ECS instances of the VPC network can provide public services by configuring IP mapping or port mapping.