fck-nat

https://github.com/AndrewGuenther/fck-nat/blob/main/service/... this is the bit you need to understand. You've got the gist of it, but you probably want to read about NAT and iptables. The source destination check is important - but implementation specific here. Google Cloud does it like this - https://cloud.google.com/vpc/docs/using-routes#canipforward From the VPC perspective, the key here is understanding that subnets within VPCs have route tables that determine where traffic from your subnet goes next. In this case traffic to the internet is sent to an interface on the NAT instance.

There is an ongoing discussion about adding NAT64 support: https://github.com/AndrewGuenther/fck-nat/issues/41

If you're up for it... https://github.com/AndrewGuenther/fck-nat Even has ha mode.

NAT Gateways also support bandwidth, availability, and performance properties that most customers just don't need. AWS networking services which charge by GB processed are always a cost disaster waiting to happen. I built my own NAT AMI[1] that costs <$4/month and has zero bandwidth charges and is good enough for most people. [1]: https://github.com/AndrewGuenther/fck-nat/