How to pass variable in file() of terraform - file

Question

It is required to create cloudfront public key using terraform, Here public key is separate based on environment and its stored as {env_name}.pem in directory name public-key-cf.
env_name can be dev,stage,prod.
To achieve this below terraform block is used:
resource "aws_cloudfront_public_key" "documents-signing-key" {
name = "cf-public-key"
comment = "Public Key"
encoded_key = file("${path.module}/public-key-cf/"${var.environment}".pem)"
}
I am getting error as :
This character is not used within the language.
How to fix this issue?
Thanks.

Answer 1

You seem to have syntax issues within your code and have used quotes in the wrong places. Please refer to String Templates for string interpolations in terraform.
This is the structure I have used to simulate your query.
.
├── dependencies.tf
├── file_function_variable.tf
├── main.tf
└── public-key-cf
└── dev.pub
Where file_function_variable.tf is the one where we focus mostly.
## File function within a sting input (multiple string interpolation).
resource "aws_security_group" "file_function_variable" {
name = "allow_tls"
description = "Allow TLS inbound traffic with ${file("${path.module}/public-key-cf/${var.environment}.pub")}"
vpc_id = local.vpc_id
tags = {
Name = "allow_tls"
}
}
## usage of explicit file function.
resource "aws_cloudfront_public_key" "documents-signing-key" {
name = "cf-public-key"
comment = "Public Key"
encoded_key = file("${path.module}/public-key-cf/${var.environment}.pub")
}
variable "environment" {
type = string
description = "(optional) Environment for the deployment"
default = "dev"
}
The above code has generated the below plan, to verify how will it look like.
➜ stackoverflow tf plan <aws:sre>
Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the
following symbols:
+ create
Terraform will perform the following actions:
# aws_cloudfront_public_key.documents-signing-key will be created
+ resource "aws_cloudfront_public_key" "documents-signing-key" {
+ caller_reference = (known after apply)
+ comment = "Public Key"
+ encoded_key = <<-EOT
ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAII3EZdb2OUzuMtgxCp5nyR3SmXs1Fml1Z6/kk1cyEuWf
EOT
+ etag = (known after apply)
+ id = (known after apply)
+ name = "cf-public-key"
+ name_prefix = (known after apply)
}
# aws_security_group.file_function_variable will be created
+ resource "aws_security_group" "file_function_variable" {
+ arn = (known after apply)
+ description = <<-EOT
Allow TLS inbound traffic with ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAII3EZdb2OUzuMtgxCp5nyR3SmXs1Fml1Z6/kk1cyEuWf
EOT
+ egress = (known after apply)
+ id = (known after apply)
+ ingress = (known after apply)
+ name = "allow_tls"
+ name_prefix = (known after apply)
+ owner_id = (known after apply)
+ revoke_rules_on_delete = false
+ tags = {
+ "Name" = "allow_tls"
}
+ tags_all = {
+ "Name" = "allow_tls"
}
+ vpc_id = (known after apply)
}
Conclusion:
As mentioned in another answer, it's better to use plugins/extensions while working with terraform.
For VSCode there is an official HashiCorp.terraform plugin which supports syntax highlighting and much more.

Answer 2

encoded_key = file("${path.module}/public-key-cf/"${var.environment}".pem)"
It seems to me that you made a syntactical mistake by placing the quotes in the wrong place, I think you meant to write:
encoded_key = file("${path.module}/public-key-cf/${var.environment}.pem")
If it's the same case in your code that's likely the reason behind that rather cryptic looking error message.
Consider installing a plugin for syntax checks if you haven't yet, it simplifies writing code in terraform (and in general too) by a lot.