Terraform Modules use Public Modules

Step-01: Introduction

Introduction - Module Basics
Root Module
Child Module
Published Modules (Terraform Registry)
Module Basics
Defining a Child Module
- Source (Mandatory)
- Version
- Meta-arguments (count, for_each, providers, depends_on, )
- Accessing Module Output Values
- Tainting resources within a module
Module Sources

Step-02: Defining a Child Module

We need to understand about the following
Module Source (Mandatory): To start with we will use Terraform Registry
Module Version (Optional): Recommended to use module version
Azure VNET Terraform Module
We are going to use the previous example and in that we will remove Virtual Network and Subnet Terraform Resources and use a Virtual Network Public Registry module.
c5-virrtual-network.tf

# Create Virtual Network and Subnets using Terraform Public Registry Module
module "vnet" {
  source              = "Azure/vnet/azurerm"
  version = "2.5.0"
  vnet_name = local.vnet_name
  resource_group_name = azurerm_resource_group.myrg.name
  address_space       = ["10.0.0.0/16"]
  subnet_prefixes     = ["10.0.1.0/24", "10.0.2.0/24", "10.0.3.0/24"]
  subnet_names        = ["subnet1", "subnet2", "subnet3"]

  subnet_service_endpoints = {
    subnet2 = ["Microsoft.Storage", "Microsoft.Sql"],
    subnet3 = ["Microsoft.AzureActiveDirectory"]
  }
  tags = {
    environment = "dev"
    costcenter  = "it"
  }
  depends_on = [azurerm_resource_group.myrg]
}

Step-03: Changes to Network Interface

c5-virtual-network.tf

# Create Network Interface
resource "azurerm_network_interface" "myvmnic" {
  name                = local.nic_name
  location            = azurerm_resource_group.myrg.location
  resource_group_name = azurerm_resource_group.myrg.name

  ip_configuration {
    name                          = "internal"
    #subnet_id                     = azurerm_subnet.mysubnet.id    
    subnet_id                     = module.vnet.vnet_subnets[0]
    private_ip_address_allocation = "Dynamic"
    public_ip_address_id = azurerm_public_ip.mypublicip.id 
  }
  tags = local.common_tags
}

Step-04: c6-linux-virtual-machine.tf

No changes to Linux Virtual Machine.
We reference the Network Interface only in VM Resource, so due to VNET change, no changes required in VM Resource.

Step-05: c7-outputs.tf

Define Virtual Network Module Outputs

# Output Values - Virtual Network
output "virtual_network_name" {
  description = "Virutal Network Name"
  #value = azurerm_virtual_network.myvnet.name 
  value = module.vnet.vnet_name
}
output "virtual_network_id" {
  description = "Virutal Network ID"
  value = module.vnet.vnet_id
}
output "virtual_network_subnets" {
  description = "Virutal Network Subnets"
  value = module.vnet.vnet_subnets
}
output "virtual_network_location" {
  description = "Virutal Network Location"
  value = module.vnet.vnet_location
}
output "virtual_network_address_space" {
  description = "Virutal Network Address Space"
  value = module.vnet.vnet_address_space
}

Step-06: Execute Terraform Commands

# Terraform Init
terraform init

# Terraform Validate
terraform validate

# Terraform Format
terraform fmt

# Terraform Plan
terraform plan

# Terraform Apply
terraform apply -auto-apporve

# Verify 
1) Verify in Azure Portal console , all the resources should be created.
http://<Public-IP-VM>
http://<Public-IP-VM>/app1
http://<Public-IP-VM>/app1/metadata.html

Step-07: Tainting Resources in a Module

The taint command can be used to taint specific resources within a module
Very Very Important Note: It is not possible to taint an entire module. Instead, each resource within the module must be tainted separately.

# List Resources from State
terraform state list

# Taint a Resource
terraform taint <RESOURCE-NAME>
terraform taint module.vnet.azurerm_subnet.subnet[2]

# Terraform Plan
terraform plan
Observation: 
1. Subnet2 will be destroyed and re-created

# Terraform Apply
terraform apply -auto-approve

Step-08: Clean-Up Resources & local working directory

# Terraform Destroy
terraform destroy -auto-approve

# Delete Terraform files 
rm -rf .terraform*
rm -rf terraform.tfstate*

Step-09: Meta-Arguments for Modules

Meta-Argument concepts are going to be same as how we learned during Resources section.
count
for_each
providers
depends_on
lifecycle
Meta-Arguments for Modules

Step-10: Discuss about Module Sources

Module Sources