How to use existing VMs in the Backend Pool while creating a new Internal Load Balancer in Azure via terraform

Question

Currently I'm trying to create a new Internal Load Balancer, which uses existing VMs already present in Azure. I was looking on how i can include these VMs data in the Terraform script. I did research a bit on this and found some have done it through NAT association, which doesn't work in my case, as i'm trying to deploy an Internal Load Balancer.

Please assist.

Current code:

data "azurerm_virtual_network" "vnet0001" {
  name                = "vnet0001"
  resource_group_name = "vnet-rg"
}

data "azurerm_subnet" "sub" {
  name                = "vnet00001-sub"
  resource_group_name = "vnet-rg"
}

resource "azurerm_lb" "terra-app" {
  name                = "lb-dev"
  location            = "East US2"
  resource_group_name = azurerm_resource_group.terra-app.name
  sku                 = "Standard"
  sku-tier            = "Regional"

  frontend_ip_configuration {
    name = "frontendip"
    zones = ["1", "2", "3"]
    subnet_id = azurerm_subnet.sub.id
    private_ip_address_allocation = "Dynamic"
  }
}

resource "azurerm_lb_backend_address_pool" "terra-app" {
  loadbalancer_id = azurerm_lb.terra-app.id
  name            = "lb-backendpool"
}

resource "azurerm_lb_probe" "h-probe" {
  loadbalancer_id   = azurerm_lb.terra-app.id
  name              = "hp1"
  port              = 111
  protocol          = "Tcp"
  request_path      = "/"
}

resource "azurerm_lb_rule" "lb-rule" {
  loadbalancer_id                = azurerm_lb.terra-app.id
  name                           = "lb-r1"
  protocol                       = "Tcp"
  frontend_port                  = 111
  backend_port                   = 111
  frontend_ip_configuration_name = "frontendip"
  backend_address_pool_ids       = azurerm_lb_backend_address_pool.terra-app.id
  probe_id                       = azurerm_lb_probe.terra-ipp.id
}

Answer 1

I tried to reproduce the same issue in my environment and got the below results

I have added the some script for below file

provider "azurerm" {
  features {}
}

resource "azurerm_resource_group" "my-rg-test" {
  name     = "RG-Terraform-on-Azure"
  location = "West Europe"
}

resource "azurerm_virtual_network" "my-vnet-test" {
  name                = "example-vnet"
  address_space       = ["10.0.0.0/16"]
  location            = azurerm_resource_group.my-rg-test.location
  resource_group_name = azurerm_resource_group.my-rg-test.name
}

resource "azurerm_subnet" "example" {
  name                 = "example-subnet"
  resource_group_name  = azurerm_resource_group.my-rg-test.name
  virtual_network_name = azurerm_virtual_network.my-vnet-test.name
  address_prefixes     = ["10.0.2.0/24"]
  service_endpoints    = ["Microsoft.Storage"]
}
    resource "azurerm_lb" "terra-app" {
      name                = "lb-dev"
      location            = "East US2"
      resource_group_name = azurerm_resource_group.terra-app.name
      sku                 = "Standard"
      sku-tier            = "Regional"
      
      frontend_ip_configuration {
        name = "frontendip"
        zones = ["1", "2", "3"]
        subnet_id = azurerm_subnet.sub.id
        private_ip_address_allocation = "Dynamic"!
      }
    }
    
    resource "azurerm_lb_backend_address_pool" "terra-app" {
      loadbalancer_id = azurerm_lb.terra-app.id
      name            = "lb-backendpool"
    }
    
    resource "azurerm_lb_probe" "h-probe" {
      loadbalancer_id   = azurerm_lb.terra-app.id
      name              = "hp1"
      port              = 111
      protocol          = "Tcp"
      request_path      = "/"
    }
    
    resource "azurerm_lb_rule" "lb-rule" {
      loadbalancer_id                = azurerm_lb.terra-app.id
      name                           = "lb-r1"
      protocol                       = "Tcp"
      frontend_port                  = 111
      backend_port                   = 111
      frontend_ip_configuration_name = "frontendip"
      backend_address_pool_ids       = azurerm_lb_backend_address_pool.terra-app.id
      probe_id                       = azurerm_lb_probe.terra-ipp.id
    }

I have used the some commands to execute the file

terraform init

By using this command It will initialize the configuration file

terraform plan

By using this command it will determine the what needs to be created or update or destroy to move from current state to desired state

terraform apply

By using this command it will perform the changes required to reach the desired state

When I open the portal I am able to see the load balancer which I have newly created