How to use `templatefile` when writing terraform files in JSON

Terraform
1

I am looking to grammatically create terraform files, and am therefore using the JSON Configuration syntax (JSON Configuration Syntax - Configuration Language | Terraform | HashiCorp Developer)

I was wondering how to express

resource “local_file” “user_data_json” {
count = 2
content = templatefile(“metadata_template.json”, {
SYSTEM_NAME = var.system_name
NODE_NAME = var.node_names[count.index]
NODE_ID = local.node_ids[count.index]
DNS_SERVERS = “{jsonencode(var.dns_servers)}" NTP_SERVERS = "{jsonencode(var.ntp_servers)}”
TIMEZONE = var.timezone
}
)
filename = local.userdata_files[count.index]
}

In the JSON format?

This does not work?

“resource”: {
“local_file”: {
“user_data_json”: {
“content”: “{templatefile(\"metadata_template.json\", {'NODE_ID': '{local.node_ids[count.index]}', ‘NODE_NAME’: '{var.node_names[count.index]}', 'LICENSE_KEY': {var.license}, ‘DNS_SERVERS’: ‘{jsonencode(var.management_dns_servers)}', 'NTP_SERVERS': '{jsonencode(var.ntp_servers)}’, ‘DCM_SERVERS’: '{jsonencode(var.dcm_ips)}', 'TIMEZONE': {var.timezone})}”,
“count”: 2,
“filename”: “${local.userdata_files[count.index]}”
}
}

i.e. “content”: ("${templatefile("metadata_template.json", FOO), where FOO is a JSON array.

I’m using Terraform v0.12.3

More generally is there a way to do from HCL terraform file to its JSON equivalent? A command-line tool would be very useful here.

2

Hi @andrew-lee-metaswitc,

Unfortunately the forum has interpreted parts of your configuration as TeX math because the configuration wasn’t in ``` delimiters, so I can’t see exactly what you tried here, but it should work to wrap your expression in ${ … } when you place it inside the JSON string:

{
  "example": "${jsonencode(var.dns_servers)}"
}

The JSON syntax has a special rule where if the entire string is covered by a single interpolation sequence ("${ to start and }" to end) then the result of the expression inside is used directly as the result, without first converting it to a string. In this case that special case wouldn’t matter anyway, because the result of jsonencode is a string, but that’s a good rule to keep in mind when generating Terraform configuration in JSON format.

There is not currently any automatic way to convert from native syntax to JSON syntax.

3

Ahh yes, bad block comments. To close the loop on this, I have worked out how to express

resource "local_file" "user_data_json" {
  count = 2
  content = templatefile("metadata_template.json", {
    SYSTEM_NAME                  = var.system_name
    NODE_NAME                    = var.node_names[count.index]
    NODE_ID                      = local.node_ids[count.index]
    DNS_SERVERS                  = "${jsonencode(var.dns_servers)}"
    NTP_SERVERS                  = "${jsonencode(var.ntp_servers)}"
    }
  )
  filename = "${var.node_names[count.index]}_userdata.json"
}

in JSON, it just involves lots of back slashes:

  "resource": {
    "local_file": {
      "user_data_json": {
        "content": "${templatefile(\"metadata_template.json\", {\"NODE_ID\": \"${local.node_ids[count.index]}\", \"NODE_NAME\": \"${var.node_names[count.index]}\", \"LICENSE_KEY\": \"${var.license}\", \"DNS_SERVERS\": \"${jsonencode(var.management_dns_servers)}\", \"NTP_SERVERS\": \"${jsonencode(var.ntp_servers)}\"})}",
        "count": 2,
        "filename": "${var.node_names[count.index]}_userdata.json"
      }
    },

So I’ve got what I wanted.

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