Why Do I Need DNAT?

In a public NAT gateway, DNAT enables servers in a VPC to share an EIP to provide services accessible from the Internet through IP address mapping or port mapping. For details, see Adding a DNAT Rule.

In a private NAT gateway, DNAT enables servers, regardless of if they are in the same AZ, to share the same transit IP address to provide services accessible from on-premises data centers or other VPCs. For details, see section "Adding a DNAT Rule" under "Managing Private NAT Gateways" in NAT Gateway User Guide.