title: Lookup Subnet ARN By Name in Cloudformation
body: <p>Is it possible to reference a subnet by tag name in a cloudformation script? I am in a VPC with multiple regions. Each region has subnets with tag names like "app_a", "app_b", "app_c" for application level subnets in availability zones a, b and c. Ideally, I would like to avoid putting all the subnet ARNS in a big map in the Mappings section of the template. Assuming I don't have access to outputs of another template that created the subnet, is there any other way to refer to the subnets by name?</p>