how can I insert variables into json file when using terraform - json

Question

this is the module folder structure
the json definition file (machine_definition.json)
{
"Comment": "A Hello World example of the Amazon States Language using Pass states",
"StartAt": "Hello",
"States": {
"Hello": {
"Type": "Pass",
"Result": "Hello",
"Next": "World"
},
"World": {
"Type": "${var.test}",
"Result": "World",
"End": true
}
}
}
for example I'm trying to enter var.test in here.
how to make the json file detect my variables?
here is the step function definition
module "step-functions" {
source = "terraform-aws-modules/step-functions/aws"
name = "env-${var.environment}-state-machine"
definition = file("${path.module}/machine_definition.json")
tags = var.tags
service_integrations = {
xray = {
xray = true
}
}
cloudwatch_log_group_name = "env-${var.environment}-state-machine-logGroup"
attach_policies = true
number_of_policies = 2
policies = ["arn:aws:iam::aws:policy/AmazonS3FullAccess", "arn:aws:iam::aws:policy/AWSLambda_FullAccess"]
}

Answer 1

Variables cannot be added to a file that way. In order to achieve what you want, you need to use the templatefile [1] built-in fuction. To achieve this you need a bit of code change:
definition = templatefile("${path.module}/machine_definition.json", {
type = var.test
})
Then, in the JSON file, you need to reference the templated variable (type) like this:
{
"Comment": "A Hello World example of the Amazon States Language using Pass states",
"StartAt": "Hello",
"States": {
"Hello": {
"Type": "Pass",
"Result": "Hello",
"Next": "World"
},
"World": {
"Type": "${type}",
"Result": "World",
"End": true
}
}
}
This should render the file properly.
[1] https://developer.hashicorp.com/terraform/language/functions/templatefile