> Were the AZ with the single NAT to go down, then instances in the other AZs wouldn't be able to communicate outside the VPC (ie. to the rest of the internet)

> Were the AZ with the single NAT to go down, then instances in the other AZs wouldn't be able to communicate outside the VPC (ie. to the rest of the internet) Oh I see. Though assuming app servers are wired up behind an ELB, the service will only be partially degraded (no app server outbound connectivity, like you said). The one-NAT per AZ is a more robust design but at $30/mo each (for NAT gateway) seems expensive ;) Even at $10/mo (small do-it-yourself NAT instance) it's not free.