[SOLVED] Trying to set Windows Hostname on an instance launched by Terraform

Issue

I am trying to set a hostname on a Windows instance that I have launched from AWS account by Terraform. I can set the hostname with the help of a host.ps1 script. But everytime I launch a new instance i have to manually change the hostname hard coded inside the host.ps1 script file. So i wanted to do this with the help of a variable that i can specify during runtime or with 'Terraform apply'. This is the code I am trying with but its not happening.

I would also like to do the same thing on a linux platform later and for that i know i might have to use an sh file to accomplish that, but i dont know the exact process.

Can anybody help me?

Here are my code:

main.tf:

    resource "aws_instance" "terra" {
  
   
    ami = "ami-*****"
    instance_type = "t3.xlarge"
    
    tags = {
      #Name = "terra-test-Pega8.7"
      Name = var.hostname
      Accesibility = "Public"
      
    }
    subnet_id = "subnet-0ba2da79c625a1513"
    security_groups = ["sg-0d433ad46d13b2a0c"]
    key_name = "windows-key"
    
    user_data = file("host.ps1 ${var.hostname}")  # (here i tried only the hostname first which 
                                                    worked but i wanted to put the hostname in a 
                                                    variable later , so i tried this)
  

}
  
  variable "hostname" {
     type = string
     description = "Sets a hostname of the created instance"
     #default = "terratest"
   } 


resource "aws_eip_association" "eip_assoc" {
  instance_id   = aws_instance.terra.id
  allocation_id = aws_eip.elasticip.id
}

resource "aws_eip" "elasticip" {
  vpc = true
}

here is the host.ps1 file:

param([String]$hname)
Rename-Computer -NewName $hname -Force -Restart

Here is the code first which worked previously

Rename-Computer -NewName 'terratest' -Force -Restart

**Actually i am very new to this so dont know much about these codes, so if anybody can guide that will be very helpful. Thank you in advance.

Solution

You're trying to pass parameters in something that's loading up a file for your user_data which won't work. If you want to pass terraform variables into your user_data, you could try inlining your bootstrap script into the terraform file:

resource "aws_instance" "terra" {
  // Your stuff here

  user_data = <<EOF
<powershell>
  Rename-Computer -NewName ${var.hostname} -Force -Restart
</powershell>
EOF
}

A neater way would be to use a template_file:

data "template_file" "user_datapowershell" {
  template = <<EOF
<powershell>
Rename-Computer -NewName ${var.hostname} -Force -Restart
</powershell>
EOF
}

resource "aws_instance" "terra" {
  // Your stuff here

  user_data = data.template_file.user_datapowershell.rendered
}

Answered By - Majdie Gideir

Answer Checked By - Dawn Plyler (WPSolving Volunteer)