Define input variables

4min
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Terraform

You now have enough Terraform knowledge to create useful configurations, but the examples so far have used hard-coded values. Terraform configurations can include variables to make your configuration more dynamic and flexible.

Note

This tutorial builds on configuration from an earlier tutorial. If you have not yet completed it, do so now.

Define your variables

In your learn-terraform-azure directory, create a new file called variables.tf. Copy and paste the variable declaration below.

variable "resource_group_name" {
  default = "myTFResourceGroup"
}

This declaration includes a default value for the variable, so the resource_group_name variable will not be a required input.

Update your Terraform configuration with your variables

Update your azurerm_resource_group configuration to use the input variable for the resource group name. Modify the virtual machine block as follows:

resource "azurerm_resource_group" "rg" {
  name     = var.resource_group_name
  location = "westus2"

  tags = {
    Environment = "Terraform Getting Started"
    Team        = "DevOps"
  }
}

Apply your configuration

Re-run terraform apply to recreate your infrastructure using input variables. Respond yes to the prompt to confirm the operation.

$ terraform apply

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
  + create

Terraform will perform the following actions:
##...
Plan: 2 to add, 0 to change, 0 to destroy.

Do you want to perform these actions?
  Terraform will perform the actions described above.
  Only 'yes' will be accepted to approve.

  Enter a value: yes

azurerm_resource_group.rg: Creating...
azurerm_resource_group.rg: Creation complete after 1s [id=/subscriptions/c9ed8610-47a3-4107-a2b2-a322114dfb29/resourceGroups/myTFResourceGroup]
azurerm_virtual_network.vnet: Creating...
azurerm_virtual_network.vnet: Creation complete after 7s [id=/subscriptions/c9ed8610-47a3-4107-a2b2-a322114dfb29/resourceGroups/myTFResourceGroup/providers/Microsoft.Network/virtualNetworks/myTFVnet]

Apply complete! Resources: 2 added, 0 changed, 0 destroyed.

Now apply the configuration again, this time overriding the default resource group name by passing in a variable using the -var flag. Updating the resource group name is a destructive update that forces Terraform to recreate the resource, and in turn the virtual network that depends on it. Respond to the confirmation prompt with yes to rename the resource group and create the new resources.

$ terraform apply -var "resource_group_name=myNewResourceGroupName"
azurerm_resource_group.rg: Refreshing state... [id=/subscriptions/c9ed8610-47a3-4107-a2b2-a322114dfb29/resourceGroups/myTFResourceGroup]
azurerm_virtual_network.vnet: Refreshing state... [id=/subscriptions/c9ed8610-47a3-4107-a2b2-a322114dfb29/resourceGroups/myTFResourceGroup/providers/Microsoft.Network/virtualNetworks/myTFVnet]

An execution plan has been generated and is shown below.
Resource actions are indicated with the following symbols:
-/+ destroy and then create replacement

Terraform will perform the following actions:

  # azurerm_resource_group.rg must be replaced
-/+ resource "azurerm_resource_group" "rg" {
      ~ id       = "/subscriptions/c9ed8610-47a3-4107-a2b2-a322114dfb29/resourceGroups/myTFResourceGroup" -> (known after apply)
      ~ name     = "myTFResourceGroup" -> "myNewResourceGroupName" # forces replacement
        tags     = {
            "Environment" = "Terraform Getting Started"
            "Team"        = "DevOps"
        }
        # (1 unchanged attribute hidden)
    }

  # azurerm_virtual_network.vnet must be replaced
-/+ resource "azurerm_virtual_network" "vnet" {
      - dns_servers           = [] -> null
      ~ guid                  = "260a1a64-08ed-4693-84d8-eda800326faa" -> (known after apply)
      ~ id                    = "/subscriptions/c9ed8610-47a3-4107-a2b2-a322114dfb29/resourceGroups/myTFResourceGroup/providers/Microsoft.Network/virtualNetworks/myTFVnet" -> (known after apply)
        name                  = "myTFVnet"
      ~ resource_group_name   = "myTFResourceGroup" -> "myNewResourceGroupName" # forces replacement
      ~ subnet                = [] -> (known after apply)
      - tags                  = {} -> null
        # (3 unchanged attributes hidden)
    }

Plan: 2 to add, 0 to change, 2 to destroy.

Do you want to perform these actions?
  Terraform will perform the actions described above.
  Only 'yes' will be accepted to approve.

  Enter a value: yes

azurerm_virtual_network.vnet: Destroying... [id=/subscriptions/c9ed8610-47a3-4107-a2b2-a322114dfb29/resourceGroups/myTFResourceGroup/providers/Microsoft.Network/virtualNetworks/myTFVnet]
azurerm_virtual_network.vnet: Still destroying... [id=/subscriptions/c9ed8610-47a3-4107-a2b2-...osoft.Network/virtualNetworks/myTFVnet, 10s elapsed]
azurerm_virtual_network.vnet: Destruction complete after 11s
azurerm_resource_group.rg: Destroying... [id=/subscriptions/c9ed8610-47a3-4107-a2b2-a322114dfb29/resourceGroups/myTFResourceGroup]
azurerm_resource_group.rg: Still destroying... [id=/subscriptions/c9ed8610-47a3-4107-a2b2-...dfb29/resourceGroups/myTFResourceGroup, 10s elapsed]
azurerm_resource_group.rg: Still destroying... [id=/subscriptions/c9ed8610-47a3-4107-a2b2-...dfb29/resourceGroups/myTFResourceGroup, 20s elapsed]
azurerm_resource_group.rg: Still destroying... [id=/subscriptions/c9ed8610-47a3-4107-a2b2-...dfb29/resourceGroups/myTFResourceGroup, 30s elapsed]
azurerm_resource_group.rg: Still destroying... [id=/subscriptions/c9ed8610-47a3-4107-a2b2-...dfb29/resourceGroups/myTFResourceGroup, 40s elapsed]
azurerm_resource_group.rg: Destruction complete after 48s
azurerm_resource_group.rg: Creating...
azurerm_resource_group.rg: Creation complete after 1s [id=/subscriptions/c9ed8610-47a3-4107-a2b2-a322114dfb29/resourceGroups/myNewResourceGroupName]
azurerm_virtual_network.vnet: Creating...
azurerm_virtual_network.vnet: Creation complete after 6s [id=/subscriptions/c9ed8610-47a3-4107-a2b2-a322114dfb29/resourceGroups/myNewResourceGroupName/providers/Microsoft.Network/virtualNetworks/myTFVnet]

Apply complete! Resources: 2 added, 0 changed, 2 destroyed.

Setting variables via the command-line will not save their values. Terraform supports many ways to use and set variables so you can avoid having to enter them repeatedly as you execute commands. To learn more, follow our in-depth tutorial, Customize Terraform Configuration with Variables.

Destroy

Outputs