Terraform conditional for AWS route tables - amazon-web-services

Question

Using Terraform, I need to create a route table for a public subnet and private subnet. The resource for a 'public' route table is using gateway_id
resource "aws_route_table" "rt-public" {
route {
cidr_block = var.cidr_block
gateway_id = var.gateway_id
}
}
The 'private' route table is using nat_gateway_id:
resource "aws_route_table" "rt-private" {
route {
cidr_block = var.cidr_block
nat_gateway_id = var.gateway_id
}
}
I pass from the main.tf file a variable var.tier that indicates whether I need a 'public' or 'private' route table.
I tried the following (in the module):
resource "aws_route_table" "rt-public" {
count = var.tier == "Public" ? 1 : 0
route {
cidr_block = var.cidr_block
gateway_id = var.gateway_id
}
}
resource "aws_route_table" "rt-private" {
count = var.tier == "Private" ? 1 : 0
route {
cidr_block = var.cidr_block
nat_gateway_id = var.gateway_id
}
}
This works. But in the main.tf I also need to access the route table id. So I created an outputs.tf file as follows:
output "aws_rt_public_id" {
value = aws_route_table.rt-public.id
}
output "aws_rt_private_id" {
value = aws_route_table.rt-private.id
}
The issue is that when a 'public' route table is created, then the 'private' output is empty. I get the error message: aws_route_table.rt-private is empty tuple. The given key does not identify an element in this collection value.
Similar error message for the public version.
How can this be fixed using conditionals?

Answer 1

You can also use your condition, and return only output that is valid:
output "aws_rt_public_id" {
value = var.tier == "Public" ? aws_route_table.rt-public[0].id : null
}
output "aws_rt_private_id" {
value = var.tier == "Private" ? aws_route_table.rt-private[0].id : null
}
In the above the null, when chosen, will result in a given output removed.