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Lab description

In this lab we learn about expressions in Terraform.

Expressions

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. Create a variable of type map, so we can pass in a list of resource group names

  1. In variables.tf, add a new variable called resource_group_names, so it looks like below.

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     variable resource_groups {
   type        = map(string)
   description = "The resource groups to deploy"
 }
    
 variable "prefix" {
   type        = string
   description = "A prefix for all resources"
   default     = "contoso"
 }
    
 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"
 }

  2. Pass the values for resource group names in terraform.tfvars.

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     resource_groups = {
   dev     = "research_dev_rg"
   staging = "research_staging_rg"
   prod    = "research_prod_rg"
 }
    
 tags = {  
   cost_center = "contoso research"    
 }

  3. Remove duplicate code from main.tf, so it now looks like below

    Take a few minutes to observe the usage of for_each here.

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     terraform {
   required_providers {
     azurerm = {
       source  = "hashicorp/azurerm"
       version = "~> 4.0"
     }
   }
 }
    
 provider "azurerm" {
   features {}
 }
    
 resource "azurerm_resource_group" "demo" {
   for_each = var.resource_groups
   name     = "${var.prefix}_${each.value}"
   location = var.region
   tags     = var.tags
 }

  4. Finally, modify outputs.tf as below, so it can print out all of the resource group ids.

    NOTE: We are using a for expression here.

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     output "resource_group_ids" {
   value       = { for key, value in azurerm_resource_group.demo : key => value.id }
   description = "Resource group ids"
 }

2. Plan

  1. Run terraform destroy -auto-approve to clean up any existing resources.

    NOTE: Even though we have updated the code, Terraform knows about our existing resources and will clean them up because of the state file.

  2. Run a plan and take a moment to understand how the changes will be applied.

    By default, we deploy to North Europe (as defined in terraform.tfvars)

  3. It should look something like below:

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     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:
    
   # azurerm_resource_group.demo["dev"] will be created
   + resource "azurerm_resource_group" "demo" {
       + id       = (known after apply)
       + location = "northeurope"
       + name     = "contoso_research_dev_rg"
       + tags     = {
           + "cost_center" = "contoso research"
         }
     }
    
   # azurerm_resource_group.demo["prod"] will be created
   + resource "azurerm_resource_group" "demo" {
       + id       = (known after apply)
       + location = "northeurope"
       + name     = "contoso_research_prod_rg"
       + tags     = {
           + "cost_center" = "contoso research"
         }
     }
    
   # azurerm_resource_group.demo["staging"] will be created
   + resource "azurerm_resource_group" "demo" {
       + id       = (known after apply)
       + location = "northeurope"
       + name     = "contoso_research_staging_rg"
       + tags     = {
           + "cost_center" = "contoso research"
         }
     }
    
 Plan: 3 to add, 0 to change, 0 to destroy.
    
 Changes to Outputs:
   + resource_group_ids = {
       + dev     = (known after apply)
       + prod    = (known after apply)
       + staging = (known after apply)
     }

3. Apply

When ready, run a terraform apply

4. Verify

  1. Verify the output and resources on Azure portal (or cli)

    The output should look something like below.

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     Apply complete! Resources: 3 added, 0 changed, 0 destroyed.
    
 Outputs:
    
 resource_group_ids = {
   "dev" = "/subscriptions/b857908d-3f5c-4477-91c1-0fbd08df4e88/resourceGroups/contoso_research_dev_rg"
   "prod" = "/subscriptions/b857908d-3f5c-4477-91c1-0fbd08df4e88/resourceGroups/contoso_research_prod_rg"
   "staging" = "/subscriptions/b857908d-3f5c-4477-91c1-0fbd08df4e88/resourceGroups/contoso_research_staging_rg"
 }

5. Commit your code

  1. git add and commit as we’ve done before.

6. Recap

Take a few minutes to have glance through the different topics we’ve covered here under expressions.

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