When using terraform with heroku, is there a way to refresh app state after an addon is attached?

Question

I'm using terraform to set up an app on heroku. The app needs a mysql database and I'm using ClearDB addon for that. When ClearDB is attached to the app, it sets a CLEARDB_DATABASE_URL config variable. The app requires the database url to be in a DATABASE_URL config variable. So what I'm trying to do is to use resource heroku_app_config_association to copy the value from CLEARDB_DATABASE_URL to DATABASE_URL. The problem is that after heroku_app resource is created, its state does not yet contain CLEARDB_DATABASE_URL, and after heroku_addon is created, the state of heroku_app is not updated.

This is the content of my main.tf file:

provider "heroku" {}

resource "heroku_app" "main" {
  name = var.app_name
  region = "eu"
}

resource "heroku_addon" "database" {
    app = heroku_app.main.name
    plan = "cleardb:punch"
}

resource "heroku_app_config_association" "main" {
    app_id = heroku_app.main.id
    sensitive_vars = {
        DATABASE_URL = heroku_app.main.all_config_vars.CLEARDB_DATABASE_URL
    }
    depends_on = [
        heroku_addon.database
    ]
}

This is the error that I get:

Error: Missing map element

  on main.tf line 22, in resource "heroku_app_config_association" "main":
  22:           DATABASE_URL = heroku_app.main.all_config_vars.CLEARDB_DATABASE_URL
    |----------------
    | heroku_app.main.all_config_vars is empty map of string

This map does not have an element with the key "CLEARDB_DATABASE_URL".

The configuration variable is copied successfully when terraform apply is executed second time. Is there a way to make it work on the first run?

Answer 1

To get up-to-date state of the heroku_app resource I used the data source:

data "heroku_app" "main" {
    name = heroku_app.main.name
    depends_on = [
        heroku_addon.database
    ]
}

I could then access the value in heroku_app_config_association resource:

resource "heroku_app_config_association" "main" {
    app_id = heroku_app.main.id
    sensitive_vars = {
        DATABASE_URL = data.heroku_app.main.config_vars.CLEARDB_DATABASE_URL
    }
}