Getting an Environment Variable in Terraform configuration?

Question

I have two environment variables. One is TF_VAR_UN and another is TF_VAR_PW. Then I have a terraform file that looks like this.

resource "google_container_cluster" "primary" {     name = "marcellus-wallace"     zone = "us-central1-a"     initial_node_count = 3      master_auth {         username = ${env.TF_VAR_UN}         password = ${env.TF_VAR_PW}     }      node_config {         oauth_scopes = [             "https://www.googleapis.com/auth/compute",             "https://www.googleapis.com/auth/devstorage.read_only",             "https://www.googleapis.com/auth/logging.write",             "https://www.googleapis.com/auth/monitoring"         ]     } } 

The two values I'd like to replace with the environment variables TF_VAR_UN and TF_VAR_PW are the values username and password. I tried what is shown above, with no success, and I've toyed around with a few other things but always get syntax issues.

Answer 1

I would try something more like this, which seems closer to the documentation.

variable "UN" {   type = string }  variable "PW" {   type = string }  resource "google_container_cluster" "primary" {   name = "marcellus-wallace"   zone = "us-central1-a"   initial_node_count = 3    master_auth {     username = var.UN     password = var.PW   }    node_config {     oauth_scopes = [         "https://www.googleapis.com/auth/compute",         "https://www.googleapis.com/auth/devstorage.read_only",         "https://www.googleapis.com/auth/logging.write",         "https://www.googleapis.com/auth/monitoring"     ]   } } 

With the CLI command being the below.

TF_VAR_UN=foo TF_VAR_PW=bar terraform apply 

Answer 2

The use of interpolation syntax throws warning with terraform v0.12.18. Now you don't need to use the interpolation syntax. You can just reference it as var.hello.

Caution : One important thing to understand from a language standpoint is that, you cannot declare variables using environment variables. You can only assign values for declared variables in the script using environment varibles. For example, let's say you have the following .tf script

variable "hello" { type=string }

Now if the environment has a variable TF_VAR_hello="foobar", during runtime the variable hello will have the value "foobar". If you assign the variable without the declaration of the variable there will not be any effect.