We have observed that your Amazon VPC resources are using a shared NAT Gateway across multiple Availability Zones (AZ). To ensure high availability and minimize inter-AZ data transfer costs, we recommend utilizing separate NAT Gateways in each AZ and routing traffic locally within the same AZ.
Each NAT Gateway operates within a designated AZ and is built with redundancy in that zone only. As a result, if the NAT Gateway or AZ experiences failure, resources utilizing that NAT Gateway in other AZ(s) also get impacted. Additionally, routing traffic from one AZ to a NAT Gateway in a different AZ incurs additional inter-AZ data transfer charges. We recommend choosing a maintenance window for architecture changes in your Amazon VPC.
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