how to dynamically pass parameter to terraform module and run a module based on a condition - terraform

Question

I have a requirement to run modules on conditional basis and also to build the parameter list for the called module dynamically from map variable.
My main.tf file looks like below
provider "aws" {
region = var.region
}
module "CreateResource1" {
source = "./modules/CreateResource1"
ProductName = "Test1"
ProductColour = "Red"
ProductShape = "Hexagone"
}
module "CreateResource2" {
source = "./modules/CreateResource2"
ProductName = "Test2"
ProductType = "xyz"
ProductModel = "abc"
ProductPrice = ""
}
the requirement is a conditional variable module_name which user will pass and based on that i need to execute any one of the modules as per condition.
Also instead of passing the parameter like ProductName, ProductColour, ProductShape as a separate variables the user will be passing them as a dict variable and i would like to build the variable dynamically with both key and value for the module.
Input from user will be like below.
module "Resource" {
module_name = "CreateResource1"
parameters = {
ProductName = "Test1"
ProductColour = "Red"
ProductShape = "Hexagone"
}
}
based on above inputs i need to select the module to run and build parameters for the module.
as i am new to terraform any leads will be appreciated.
Terraform Version used is 1.0.0
Regards

Answer 1

If possible, I would just change the modules to accept a map like the calling module:
(Disclaimer: partial, untested example)
modules/resource/main.tf
variable "module_name" {
type = string
}
variable "parameters" {
type = map
}
module "CreateResource1" {
source = "../CreateResource1"
count = var.module_name == "CreateResource1" ? 1 : 0
parameters = var.parameters
}
module "CreateResource2" {
source = "../CreateResource2"
count = var.module_name == "CreateResource2" ? 1 : 0
parameters = var.parameters
}
main.tf
module "Resource" {
source = "./modules/resource"
module_name = "CreateResource1"
parameters = {
ProductName = "Test1"
ProductColour = "Red"
ProductShape = "Hexagone"
}
}
The modules that are called would need a small modification to define a parameter input variable of type map and then the values could be accessed in the code using a lookup function (e.g. lookup(var.parameters, "ProductName", "") - note the 3rd param allows you to specify a default if the element does not exist in the map. There is no reason why that value cannot be taken from an input variable, so if you don't want to hard code it here, you could for example, pass it in from a default set in the calling module, and passed into all/some of the children). So for example:
modules/CreateResource1/main.tf (Partial example)
variable "parameters" {
type = map
}
resource "some_resource_type" "some_resource_name" {
ProductName = lookup(var.parameters, "ProductName", "Product1")
ProductColour = lookup(var.parameters, "ProductColour", "Red")
ProductShape = lookup(var.parameters, "ProductShape", "Circle")
}
So in this example, the resource created by CreateResource1 requires 3 params. If they exist in the map that is passed by module Resource then they will be used, and for any that are not present in the map that is passed in, the defaults will be used (in this case "Product1", "Red" & "Circle").