Absolutely correct. We are using NAT Gateways in our architecture, and I love not having to manage it all myself, but it is definitely a tradeoff in costs.
From the AWS documentation [1]:
"Each NAT gateway is created in a specific Availability Zone and implemented with redundancy in that zone. You have a limit on the number of NAT gateways you can create in an Availability Zone. For more information, see Amazon VPC Limits.
Note
If you have resources in multiple Availability Zones and they share one NAT gateway, in the event that the NAT gateway’s Availability Zone is down, resources in the other Availability Zones lose Internet access. To create an Availability Zone-independent architecture, create a NAT gateway in each Availability Zone and configure your routing to ensure that resources use the NAT gateway in the same Availability Zone."
From the AWS documentation [1]:
"Each NAT gateway is created in a specific Availability Zone and implemented with redundancy in that zone. You have a limit on the number of NAT gateways you can create in an Availability Zone. For more information, see Amazon VPC Limits.
Note If you have resources in multiple Availability Zones and they share one NAT gateway, in the event that the NAT gateway’s Availability Zone is down, resources in the other Availability Zones lose Internet access. To create an Availability Zone-independent architecture, create a NAT gateway in each Availability Zone and configure your routing to ensure that resources use the NAT gateway in the same Availability Zone."
[1]: https://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/vpc-n...