Search code examples
terraform

Terraform outputs 'Error: Variables not allowed' when doing a plan

I've got a variable declared in my variables.tf like this:

variable "MyAmi" {
  type = map(string)
}

but when I do:

terraform plan -var 'MyAmi=xxxx'

I get:

Error: Variables not allowed

  on <value for var.MyAmi> line 1:
  (source code not available)

Variables may not be used here.

Minimal code example:

test.tf 

provider "aws" {
}

# S3
module "my-s3" {
  source = "terraform-aws-modules/s3-bucket/aws"

  bucket = "${var.MyAmi}-bucket"
}

variables.tf 

variable "MyAmi" {
  type = map(string)
}

terraform plan -var 'MyAmi=test'

Error: Variables not allowed

  on <value for var.MyAmi> line 1:
  (source code not available)

Variables may not be used here.

Any suggestions?

Solution

  • I see two things that could be causing the error you are seeing. Link to terraform plan documentation.

    1. When running terraform plan, it will automatically load any .tfvars files in the current directory. If your .tfvars file is in another directory you must provide it as a -var-file parameter. You say in your question that your variables are in a file variables.tf which means the terraform plan command will not automatically load that file. FIX: rename variables.tf to variables.tfvars

    2. When using the -var parameter, you should ensure that what you are passing into it will be properly interpreted by HCL. If the variable you are trying to pass in is a map, then it needs to be parse-able as a map.

    Instead of terraform plan -var 'MyAmi=xxxx' I would expect something more like terraform plan -var 'MyAmi={"us-east-1":"ami-123", "us-east-2":"ami-456"}'.

    See this documentation for more on declaring variables and specifically passing them in via the command line.