Unable to fetch data using external data source - azure

Question

I am trying to fetch values from azure using external data source in terraform. However, i dont understand what am i doing wrong when i try to export values using write-output, getting an error
data.external.powershell_test: data.external.powershell_test: command "Powershell.exe" produced invalid JSON: invalid character 'l' looking for beginning of object key string"
Below is my script
$vm=(Get-AzureRmVM -ResourceGroupName MFA-RG -Name vm2).name | convertTo-json
Write-Output "{""first"" : ""$vm""}"
Main.tf file
data "external" "powershell_test" {
program = ["Powershell.exe", "./vm.ps1"]
}
output "value" {
value = "${data.external.powershell_test.result.first}"
}
Can someone tel me what wrong with the script ? and if i am using write-out properly ?
Edited-------------
Below is the screenshot when i run vm.ps1 directly
Also, when i directly assign value to a variable as below, terraform is able to execute the code.
$vm = "testvm"
Write-Output "{""first"" : ""$vm""}"

Answer 1

For your issue, you should change your PowerShell command like this:
$vm=(Get-AzureRmVM -ResourceGroupName MFA-RG -Name vm2).name | convertTo-json
Write-Output "{""first"" : $vm}"
And you could change the code in the data source like this or not, but I suggest you do this:
data "external" "powershell_test" {
program = ["Powershell.exe", "${path.module}/vm.ps1"]
}
The result on my side is below:
I use the new Azure PowerShell module Az and my code shows here:
PowerShell:
$vm=(Get-AzVM -ResourceGroupName charles -Name azureUbuntu18).name | convertTo-json
Write-Output "{""first"" : $vm}"
Terraform:
data "external" "powershell_test" {
program = ["Powershell.exe", "${path.module}/vm.ps1"]
}
output "value" {
value = "${data.external.powershell_test.result.first}"
}

Answer 2

data.external.powershell_test.result is the only valid attribute, and it is map.
So the code will be changed to
output "value" {
value = "${data.external.powershell_test.result['first']}"
}
Reference:
https://www.terraform.io/docs/configuration-0-11/interpolation.html#user-map-variables

Answer 3

Thanks Charles XU for the answer. I was looking for Azure Application Gateway and after lots of digging I ended up here, as Terraform is yet to provide a data source for Azure Application Gateway. However, the same can be done using shell script and azure rest API.
Using Shell Script
appgw.sh
#!/bin/bash
#Linux: Requires Azure cli and jq to be available
#Getting Application Gateway ID using azure application gateway rest API, az cli as data source doesn't exist for it.
appgwid=$(az rest -m get --header "Accept=application/json" -u 'https://management.azure.com/subscriptions/{subscription-id}/resourceGroups/newrg/providers/Microsoft.Network/applicationGateways?api-version=2020-07-01' | jq '.value[].id')
#Terraform External Data Source requires an output, else it will return in unmarshal json error with }
echo "{\"appgw_id\" : $appgwid}"
data.tf
data "external" "appgw_id_sh" {
program = ["/bin/bash", "${path.module}/appgw.sh"]
}
outputs.tf
output "appgw_id_sh" {
value = data.external.appgw_id_sh.result.appgw_id
}
Using Powershell
appgw.ps1
#Windows: Require Azure Powershell to be available
#1. Install-Module -Name PowerShellGet -Force
#2. Install-Module -Name Az -AllowClobber
#Getting Application Gateway ID using AzApplicationGateway AzResource as data source doesn't exist for it.
$appGw = (Get-AzApplicationGateway -Name "appgw-name" -ResourceGroupName "appgw-rg-name").id | convertTo-json
#Terraform External Data Source requires an output, else it will return in unmarshal json error with }
Write-Output "{""appgw_id"" : $appgw}"
data.tf
data "external" "appgw_id_ps" {
program = ["Powershell.exe", "${path.module}/appgw.ps1"]
}
outputs.tf
output "appgw_id_ps" {
value = data.external.appgw_id_ps.result.appgw_id
}

Answer 4

FYI - when I use powershell 7, I need to use pwsh.exe instead of powershell.exe inside program code.
data "external" "powershell_test" {
program = ["**pwsh.exe**", "${path.module}/vm.ps1"]
}