Terraform Conditional Expressions

Step-01: Introduction

• Learn Terraform Conditional Expressions in Terraform
• Conditional Expression: A conditional expression uses the value of a bool expression to select one of two values.

# Example-1
condition ? true_val : false_val

# Example-2
var.a != "" ? var.a : "default-a"

Step-02: c2-variables.tf

• In extension to previous section Terraform Local Values, we have added Conditional Expressions in local values block.
• As part of that we have added two more variables in c2-variables.tf for this demo

# 6. Virtual Network Address - Dev
variable "vnet_address_space_dev" {
  description = "Virtual Network Address Space for Dev Environment"
  type = list(string)
  default = ["10.0.0.0/16"]
}

# 7. Virtual Network Address - 
variable "vnet_address_space_all" {
  description = "Virtual Network Address Space for All Environment except Dev"
  type = list(string)
  default = ["10.1.0.0/16", "10.2.0.0/16", "10.3.0.0/16"]
}

Step-03: c3-local-values.tf

• In extension to previous section Terraform Local Values, we have added Conditional Expressions in local values block.

# Local Values Block

locals {
  # Use-case-1: Shorten the names for more readability
  rg_name = "${var.business_unit}-${var.environment}-${var.resoure_group_name}"
  vnet_name = "${var.business_unit}-${var.environment}-${var.virtual_network_name}"

  # Use-case-2: Common tags to be assigned to all resources
  service_name = "Demo Services"
  owner = "Kalyan Reddy Daida"
  common_tags = {
    Service = local.service_name
    Owner   = local.owner
  }

  # Use-case-3: Terraform Conditional Expressions
  # We will learn this when we are dealing with Conditional Expressions
  # The expressions assigned to local value names can either be simple constants or can be more complex expressions that transform or combine values from elsewhere in the module.
  # With Equals (==)
  vnet_address_space = (var.environment == "dev" ? var.vnet_address_space_dev : var.vnet_address_space_all)
  # With Not Equals (!=)
  #vnet_address_space = (var.environment != "dev" ? var.vnet_address_space_all : var.vnet_address_space_dev)
}

Step-04: c5-virtual-network.tf

• Reference address_space argument with local value.

# Create Virtual Network
resource "azurerm_virtual_network" "myvnet" {
  #name                = "${var.business_unit}-${var.environment}-${var.virtual_network_name}"
  name                = local.vnet_name
  #address_space       = ["10.0.0.0/16"]
  address_space       = local.vnet_address_space
  location            = azurerm_resource_group.myrg.location
  resource_group_name = azurerm_resource_group.myrg.name
  tags = local.common_tags
}

Step-05: Execute Terraform Commands

# Terraform Initialize
terraform init

# Terraform Validate
terraform validate

# Terraform Plan: When Variable values, environment = dev 
terraform plan
Observation: 
1) Plan will generate vnet `address_space` with 1 value


# Terraform Plan: When Variable values, environment = qa
terraform plan
1) Plan will generate vnet `address_space` with 3 values


# Terraform Apply (Optional)
terraform apply -auto-approve

Step-06: c5-virtual-network.tf

• Understand and implement Terraform Conditional Expressions in Resources

# Create Virtual Network - Conditional Expressions in a Resource Demo
resource "azurerm_virtual_network" "myvnet2" {
  #count = 2
  count = var.environment == "dev" ? 1 : 5
  name                = "${var.business_unit}-${var.environment}-${var.virtual_network_name}-${count.index}"
  address_space       = ["10.0.0.0/16"]
  location            = azurerm_resource_group.myrg.location
  resource_group_name = azurerm_resource_group.myrg.name
  tags = local.common_tags
}

# Terraform Plan: When Variable values, environment = dev 
terraform plan
Observation: 
1) Plan will generate with 1 Virtual Network for  azurerm_virtual_network.myvnet2 Resource

# Terraform Plan: When Variable values, environment = qa 
terraform plan
Observation: 
1) Plan will generate with 5 Virtual Network for  azurerm_virtual_network.myvnet2 Resource

Step-07: Clean-Up

# Terraform Destroy
terraform destroy -auto-approve

# Clean-Up
rm -rf .terraform*
rm -rf terraform.tfstate*

# Uncomment and Comment right values in c2-variables.tf (Roll back to put ready for student demo)
- For "environment" Variable, enable default = "dev"