Setting a resource block parameter based on a boolean

Question

I am trying to create a Terraform project for Aurora PostgreSQL and would like to have a variable defined whether it's serverless or not, if possible at all. For example:

1. variables.tf:

   variable "serverless" {type = bool}

2. terraform.tfvars:

   serveless = "true"

3. main.tf (pseudo code):

   resource "aws_rds_cluster" "db_cluster" {
   ...
   
   if var.serveless == true ? 
       serverlessv2_scaling_configuration {
         max_capacity = 16
         min_capacity = 0.5
       }
   : []
   
   

If the variable is true - set the serverless code, otherwise - don't include it at all.

Answer 1

It is probably a good candidate to use for_each [1] and dynamic [2] block combined. In that case, you would have something like:

resource "aws_rds_cluster" "example" {
  # ... other configuration ...

  dynamic "serverlessv2_scaling_configuration" {
    for_each = var.serveless ? [1] : []
    content {
      max_capacity = var.max_capacity
      min_capacity = var.min_capacity
    }
  }
}

Take care also about the note for Aurora Severless:

serverlessv2_scaling_configuration configuration is only valid when engine_mode is set to provisioned

So you might also want to use the ternary expression in that case.

---

[1] https://www.terraform.io/language/meta-arguments/for_each

[2] https://www.terraform.io/language/expressions/dynamic-blocks