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Lab description

In this lab we learn about the variable definition in Terraform.

Variables

Setup

Make sure you are in the correct folder:

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cd ~/terraform-labs

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cd ~/terraform-labs

If you were unable to complete the last lab, you can find a copy of the files in the solutions folder

1. Refactor main.tf to make it more configurable using variables

Introduce variables to main.tf

Notice how each variable has a slightly different setup. We’ve done this, so we can try different approaches to pass in data:

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terraform {
  required_providers {
    azurerm = {
      source  = "hashicorp/azurerm"
      version = "~> 4.0"
    }
  }
}

provider "azurerm" {
  features {}
}

variable "prefix" {}

variable "region" {
  type        = string
  default     = "North Europe"
  description = "The Azure region to deploy resources"
  validation {
    condition     = contains(["UK South", "UK West", "North Europe", "West Europe", "East US", "West US"], var.region)
    error_message = "Invalid region"
  }
}

variable "tags" {
  type        = map(any)
  description = "A map of tags"
}

resource "azurerm_resource_group" "contoso_rg" {
  name     = "${var.prefix}_rg"
  location = var.region
  tags     = var.tags
}

resource "azurerm_resource_group" "contoso_dev_rg" {
  name     = "${var.prefix}_dev_rg"
  location = var.region
  tags     = var.tags
}

2. terraform.tfvars

  1. Create a file called terraform.tfvars.

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     cd ~/terraform-labs
 code terraform.tfvars

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     cd ~/terraform-labs
 code terraform.tfvars

  2. Add tag inputs to terraform.tfvars so it looks like below.

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     # terraform.tfvars
 tags = {  
   cost_center = "contoso research"    
 }

3. Plan and Apply

  1. Now, run a terraform plan. When prompted for var.prefix, enter contoso:

    • You should something like below, stating that there will be a force replacement.
    • This is because, now our default region is set to “North Europe” and we are not passing any overrides.
    • We are prompted for prefix because we haven’t set any default value
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     azurerm_resource_group.contoso_dev_rg: Refreshing state... [id=/subscriptions/b857908d-3f5c-4477-91c1-0fbd08df4e88/resourceGroups/contoso_dev_rg]
 azurerm_resource_group.contoso_rg: Refreshing state... [id=/subscriptions/b857908d-3f5c-4477-91c1-0fbd08df4e88/resourceGroups/contoso_rg]
    
 Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
 -/+ destroy and then create replacement
    
 Terraform will perform the following actions:
    
   # azurerm_resource_group.contoso_dev_rg must be replaced
 -/+ resource "azurerm_resource_group" "contoso_dev_rg" {
       ~ id         = "/subscriptions/b857908d-3f5c-4477-91c1-0fbd08df4e88/resourceGroups/contoso_dev_rg" -> (known after apply)
       ~ location   = "uksouth" -> "northeurope" # forces replacement
         name       = "contoso_dev_rg"
         tags       = {
             "cost_center" = "contoso research"
         }
         # (1 unchanged attribute hidden)
     }
    
   # azurerm_resource_group.contoso_rg must be replaced
 -/+ resource "azurerm_resource_group" "contoso_rg" {
       ~ id         = "/subscriptions/b857908d-3f5c-4477-91c1-0fbd08df4e88/resourceGroups/contoso_rg" -> (known after apply)
       ~ location   = "uksouth" -> "northeurope" # forces replacement
         name       = "contoso_rg"
         tags       = {
             "cost_center" = "contoso research"
         }
         # (1 unchanged attribute hidden)
     }
    
 Plan: 2 to add, 0 to change, 2 to destroy.

  2. When ready, do a terraform apply and enter contoso when prompted for prefix. (and then enter yes when asked for approval).

4. Verify the updates and commit your code

  1. Open your .gitignore file and comment out line 16. It should be changed from *.tfvars to #*.tfvars. This enables us to commit the tfvars file to source control.
  2. This time when doing a git add ., you will also see terraform.tfvars being added.

5. Environment Variables and custom .tfvars

  1. We are currently passing in the prefix manually from cli. Let’s set an environment variable, so it get’s picked from there.

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     $env:TF_VAR_prefix="contoso"
 Write-Host $env:TF_VAR_prefix

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     export TF_VAR_prefix="contoso"
 echo $TF_VAR_prefix

  2. Now create two new files for .tfvars such as below, so we can make the region configurable. (this could also be something like .dev.tfvars, .prod.tfvars in real world scenarios)

    • contoso.uk.tfvars
    • contoso.europe.tfvars
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     cd ~/terraform-labs
 Set-Content -Value "region = `"UK South`"" -Path "contoso.uk.tfvars"
 Set-Content -Value "region = `"North Europe`"" -Path "contoso.europe.tfvars"

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     cd ~/terraform-labs
 echo 'region = "UK South"' > contoso.uk.tfvars
 echo 'region = "North Europe"' > contoso.europe.tfvars

    Take a quick look at both .tfvars files and make sure they have the correct region value.

6. Plan and Apply

  1. Run a plan and apply using contoso.uk.tfvars file

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     terraform plan -var-file="contoso.uk.tfvars"
 terraform apply -auto-approve -var-file="contoso.uk.tfvars"

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     terraform plan -var-file="contoso.uk.tfvars"
 terraform apply -auto-approve -var-file="contoso.uk.tfvars"

  2. Notice that we are no longer prompted for prefix value. Terraform now picks this up from the environment variable we created.

7. Verify and commit

  1. Verify that the resource groups are re-created in UK South.
  2. Commit your code. This time when doing a git add ., you will also see two new .tfvars being added.

8. Variables.tf

In this step, we will move all the variable definitions to a separate file, so our config file (main.tf) looks tidy.

  1. Create a variables.tf file

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     cd ~/terraform-labs
 code variables.tf

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     cd ~/terraform-labs
 code variables.tf

  2. Move all the variable definitions to this file, so it looks like below.

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     variable "prefix" {}
    
 variable "region" {
   type        = string
   default     = "North Europe"
   description = "The Azure region to deploy resources"
   validation {
     condition     = contains(["UK South", "UK West", "North Europe", "West Europe", "East US", "West US"], var.region)
     error_message = "Invalid region"
   }
 }
    
 variable "tags" {
   type        = map(any)
   description = "A map of tags"
 }

  3. Don’t forget to delete the variables from main.tf.

9. Plan and Apply

Run a terraform plan and apply, but this time pass in the other .tfvars file (contoso.europe.tfvars), so we can force a replacement.

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terraform plan -var-file="contoso.europe.tfvars"
terraform apply -auto-approve -var-file="contoso.europe.tfvars"

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terraform plan -var-file="contoso.europe.tfvars"
terraform apply -auto-approve -var-file="contoso.europe.tfvars"

10. Verify results and Commit your code

  1. Verify that the resource groups are re-created in North Europe.
  2. Commit your code to git.

11. Recap

Take a few minutes to observe and recap on different value sources that are used for our variables.

Your folder should look like below. Make sure you are fully comfortable with what those files are.

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📂terraform-labs
┣ 📂.terraform
┣ 📜.gitignore
┣ 📜.terraform.lock.hcl
┣ 📜contoso.europe.tfvars
┣ 📜contoso.tfplan
┣ 📜contoso.uk.tfvars
┣ 📜main.tf
┣ 📜terraform.tfstate
┣ 📜terraform.tfstate.backup
┣ 📜terraform.tfvars
┗ 📜variables.tf

12. Topics covered

Next Lab - Outputs

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