Hclwrite(v2) a object with a reference value

Terraform
1

Hi,

We works on golang programm to generate terraform files and I am having difficulty generating a local of type object with a value reference, like this :

locals {
  servers = {
    "admin@server-1" = {
      hostname = "srv1"
      login    = "admin"
      password = data.vault_generic_secret.srv1.data["password"]
      port     = 22
    }
    "admin@server-2" = {
      hostname = "srv2"
      login    = "admin"
      password = data.vault_generic_secret.srv2.data["password"]
      port     = 22
    }
  }
}

An example of code to generate this file :

package main

import (
	"fmt"

	"github.com/hashicorp/hcl/v2/hclwrite"
	"github.com/zclconf/go-cty/cty"
)

func main() {
	f := hclwrite.NewEmptyFile()
	rootBody := f.Body()
	localsBlock := rootBody.AppendNewBlock("locals", nil).Body()
	localsBlock.SetAttributeValue("servers",
		cty.ObjectVal(map[string]cty.Value{
			"admin@server-1": cty.ObjectVal(map[string]cty.Value{
				"hostname": cty.StringVal("srv1"),
				"login":    cty.StringVal("admin"),
				"password": <?>,
				"port":     cty.NumberIntVal(22),
			}),
			"admin@server-2": cty.ObjectVal(map[string]cty.Value{
				"hostname": cty.StringVal("srv2"),
				"login":    cty.StringVal("admin"),
				"password": <?>,
				"port":     cty.NumberIntVal(22),
			}),
		}))
	fmt.Printf("%s", f.Bytes())
}

but I don’t know what to do for the reference in password

Have you an idea ?

2

Hi @jeremmfr,

hclwrite doesn’t currently have a helper function for generating this sort of expression with a mixture of literal and reference parts. Its existing helpers are only for setting entirely-literal values or single references.

I think therefore you’d need to use SetAttributeRaw to meet this use-case with today’s hclwrite. That’ll require constructing the necessary tokens yourself, because the AST layer doesn’t have any rule for doing that automatically.

Alternatively, you could generate this in a .tf.json file instead, which means you can use a normal JSON encoder rather than hclwrite. The JSON syntax equivalent of what you shared would be the following:

{
  "locals": {
    "servers": {
      "admin@server-1": {
        "hostname": "srv1",
        "login": "admin",
        "password": "${data.vault_generic_secret.srv1.data[\"password\"]}",
        "port": 22
      },
      "admin@server-2": {
        "hostname": "srv2",
        "login": "admin",
        "password": "${data.vault_generic_secret.srv2.data[\"password\"]}",
        "port": 22
      }
    }
  }
}

The Terraform language’s JSON mode exists specifically to make it easier to do this sort of dynamic generation. You can see more about how it works in JSON Configuration Syntax.

3

Thanks for your quick reply

4

Hi @apparentlymart,

I have a similar use case, but unfortunately I’m in a position where using the JSON Configuration Syntax is not possible.

How would I go on about constructing such an object using SetAttributeRaw?

I need to create the following custom_data object attribute:

post-processor "manifest" {
  custom_data = {
    subscription        = "${var.subscription_id}"
    resource_group      = "${var.resource_group}"
    gallery_name        = "${var.gallery_name}"
    image_name          = "${var.image_name}"
    image_version       = "${var.versionToBuild}"
    source_version      = "${var.info_source_version}"
    source_branch       = "${var.info_source_branch}"
    source_repo         = "${var.info_source_repo}"
    gallery_artifact_id = "/subscriptions/${var.subscription_id}/resourceGroups/${var.resource_group}/providers/Microsoft.Compute/galleries/${var.gallery_name}/images/${var.image_name}/versions/${var.versionToBuild}"
    managed_artifact_id = "/subscriptions/${var.subscription_id}/resourceGroups/${var.resource_group}/providers/Microsoft.Compute/images/${var.image_name}-${var.versionToBuild}"
  }
}

I can for instance use the following:

customDataTokens := hclwrite.Tokens{
	{
		Type: hclsyntax.ObjectConsItem
	},
	{
		Type:  hclsyntax.TokenOBrace,
		Bytes: []byte(`{`),
	},
	{
		Type:  hclsyntax.TokenCBrace,
		Bytes: []byte(`}`),
	},
}

body.SetAttributeRaw("custom_data", customDataTokens)

Which will result in:
custom_data = {}

But how should I go on about creating an attribute object which contains multiple attributes such as the custom_data object above?

Since as you’re pointing out, I’d need to use SetAttributeRaw to meet this use-case with today’s hclwrite, I’m all for that but I have no idea how to do it - an example would be super helpful and really appreciated!

Or, perhaps sine it’s been 2 years since this was posted, perhaps hclwrite now have a helper function for generating this sort of expression? :slight_smile: