Subnets
A subnet is a range of IP addresses in your VPC. You need to provide at least two subnets to create a VPC connection. Each subnet must belong a different availability zone. You can attach AWS resources, such as Amazon EC2 instances and Amazon RDS DB instances, to subnets. You can create subnets to group instances together according to your security and operational needs.
For Amazon QuickSight to connect to your database, the network needs to route traffic to the data sources that you want to reach from one of the subnets used by the QuickSight network interface. QuickSight determines which subnet to route traffic through on the backend. If the availability zone that the subnet is attached to experiences an outage, QuickSight reroutes the traffic to one of the other subnets that are configured in the VPC connection. If the data sources are on different subnets, make sure that there is a route from the QuickSight network interface to your database instance. By default, each subnet in a VPC is associated with one main route table and can reach the other subnets. For more information, see VPC and Subnets and Network ACLs in the Amazon VPC User Guide.
If you use Amazon RDS, DB instances are associated with a subnet group that you can view either
in the Amazon RDS console (https://console.aws.amazon.com/rds/
