Error: remote-exec provisioner error: host for provisioner cannot be empty

I am trying to create 2 virtual machines under a Load balancer and I am using remote-exec provisioner to install nginx server to both VM. I cannot use azurerm_public_ip properly. It doesnt pass the IP address to the host connection block of my remote-exec provisioner.

Below is my code:

# Resource Group
resource "azurerm_resource_group" "test-rg-nginx" {
name     = var.rgname
location = var.rg_location
#name     = "test-tf-test"
#location = "East US"
}
# Virtual Network
resource "azurerm_virtual_network" "test-vnet-nginx" {
name                = var.vnetname
address_space       = ["10.66.0.0/16"]
location            = azurerm_resource_group.test-rg-nginx.location
resource_group_name = azurerm_resource_group.test-rg-nginx.name
#name                = "test-tf-vnet"
}
# Subnet
resource "azurerm_subnet" "test-subnet-nginx" {
name                 = var.subnetname
resource_group_name  = azurerm_resource_group.test-rg-nginx.name
virtual_network_name = azurerm_virtual_network.test-vnet-nginx.name
address_prefixes     = ["10.66.1.0/24"]
}
# Public IPs
resource "azurerm_public_ip" "test-publicIP-VM" {
count = var.vm_count
name  = "${var.publicIP-VMname}${count.index}"
location            = azurerm_resource_group.test-rg-nginx.location
resource_group_name = azurerm_resource_group.test-rg-nginx.name
allocation_method   = "Dynamic"
}
resource "azurerm_public_ip" "test-publicIP-LB" {
name                = var.publicIP-LBname
location            = azurerm_resource_group.test-rg-nginx.location
resource_group_name = azurerm_resource_group.test-rg-nginx.name
allocation_method   = "Static"
}
#Create Load Balancer
resource "azurerm_lb" "test-lb-nginx" {
name                = var.lbname
location            = azurerm_resource_group.test-rg-nginx.location
resource_group_name = azurerm_resource_group.test-rg-nginx.name
frontend_ip_configuration {
name                 = "${var.publicIP-LBname}-frontend"
public_ip_address_id = azurerm_public_ip.test-publicIP-LB.id
}
}
resource "azurerm_lb_backend_address_pool" "lb_backendIPpool" {
loadbalancer_id = azurerm_lb.test-lb-nginx.id
name            = "BackEndAddressPool"
}
resource "azurerm_lb_probe" "http_probe" {
name            = "http_probe"
protocol        = "Tcp"
port            = 80
loadbalancer_id = azurerm_lb.test-lb-nginx.id
#resource_group_name = azurerm_resource_group.test-rg-nginx.name
}
resource "azurerm_lb_rule" "http_rule" {
name                           = "http-rule"
protocol                       = "Tcp"
frontend_port                  = 80
backend_port                   = 80
frontend_ip_configuration_name = "${var.publicIP-LBname}-frontend"
#backend_address_pool_id = azurerm_lb_backend_address_pool.lb_backendIPpool.id
probe_id        = azurerm_lb_probe.http_probe.id
loadbalancer_id = azurerm_lb.test-lb-nginx.id
#resource_group_name = azurerm_resource_group.test-rg-nginx.name
}
resource "azurerm_network_interface_backend_address_pool_association" "backendpoolAssoc" {
count                   = var.vm_count
network_interface_id    = azurerm_network_interface.test-nic[count.index].id
ip_configuration_name   = "${var.nic-ip-configname}${count.index}"
backend_address_pool_id = azurerm_lb_backend_address_pool.lb_backendIPpool.id
}
# Create network interface
resource "azurerm_network_interface" "test-nic" {
count = var.vm_count
#name = var.nicname
name                = "${var.nicname}-${count.index}"
location            = azurerm_resource_group.test-rg-nginx.location
resource_group_name = azurerm_resource_group.test-rg-nginx.name
ip_configuration {
name                          = "${var.nic-ip-configname}${count.index}"
subnet_id                     = azurerm_subnet.test-subnet-nginx.id
private_ip_address_allocation = "Dynamic"
public_ip_address_id          = azurerm_public_ip.test-publicIP-VM[count.index].id
}
}
# Network Security Group and Security rules
resource "azurerm_network_security_group" "test-nsg-nginx" {
name                = var.nsgname
location            = azurerm_resource_group.test-rg-nginx.location
resource_group_name = azurerm_resource_group.test-rg-nginx.name
security_rule {
name                       = "HTTPS"
priority                   = 100
direction                  = "Inbound"
access                     = "Allow"
protocol                   = "Tcp"
source_port_range          = "*"
destination_port_range     = "443"
source_address_prefixes    = var.address-list
destination_address_prefix = "*"
}
security_rule {
name                       = "HTTP"
priority                   = 101
direction                  = "Inbound"
access                     = "Allow"
protocol                   = "Tcp"
source_port_range          = "*"
destination_port_range     = "80"
source_address_prefixes    = var.address-list
destination_address_prefix = "*"
}
security_rule {
name                       = "SSH-Inbound"
priority                   = 102
direction                  = "Inbound"
access                     = "Allow"
protocol                   = "Tcp"
source_port_range          = "*"
destination_port_range     = "22"
source_address_prefixes    = var.address-list
destination_address_prefix = "*"
}
}
# Connect the security group to the network interface
resource "azurerm_network_interface_security_group_association" "test-sgConnect" {
count                     = var.vm_count
network_interface_id      = azurerm_network_interface.test-nic[count.index].id
network_security_group_id = azurerm_network_security_group.test-nsg-nginx.id
}
resource "azurerm_availability_set" "avset" {
name                         = "avset"
location                     = azurerm_resource_group.test-rg-nginx.location
resource_group_name          = azurerm_resource_group.test-rg-nginx.name
platform_fault_domain_count  = 2
platform_update_domain_count = 2
managed                      = true
}
#Create VM
resource "azurerm_linux_virtual_machine" "test-linux" {
count                 = var.vm_count
name                  = "${var.vm-linux}-${count.index}"
location              = azurerm_resource_group.test-rg-nginx.location
resource_group_name   = azurerm_resource_group.test-rg-nginx.name
availability_set_id   = azurerm_availability_set.avset.id
network_interface_ids = [azurerm_network_interface.test-nic[count.index].id]
size                  = var.vm-size
os_disk {
name                 = "myOsdisk-${count.index}"
caching              = "ReadWrite"
storage_account_type = "Premium_LRS"
}
source_image_reference {
publisher = "Canonical"
offer     = "0001-com-ubuntu-server-jammy"
sku       = "22_04-lts-gen2"
version   = "latest"
}
computer_name                   = var.admin-user
admin_username                  = var.admin-user
disable_password_authentication = true
#wait_for_address = true
admin_ssh_key {
username   = var.admin-user
public_key = file("${path.module}/connection/linux-pub0.pub")
}
depends_on = [
azurerm_public_ip.test-publicIP-VM
]
data "azurerm_public_ip" "publicip" {
count = var.vm_count
name                = azurerm_public_ip.test-publicIP-VM[count.index].name
resource_group_name   = azurerm_resource_group.test-rg-nginx.name
}
resource "null_resource" "default-web-server" {
count = var.vm_count
provisioner "remote-exec" {
inline = [
"sudo apt-get update",
"sudo apt-get install -y nginx",
"sudo mkdir -p /var/www/html/",
"sudo chown -R ${var.admin-user}:${var.admin-user} /var/www/html/",
"sudo chmod 644 /var/www/html/index.nginx-debian.html"
]
}
Timeouts{
read = “5m”
}
connection {
type        = "ssh"
user        = var.admin-user
private_key = file("${path.module}/connection/linux-priv0.pem")
host = "${data.azurerm_public_ip.publicip[count.index].ip_address}"
#host = data.azurerm_public_ip.publicip[count.index].fqdn
#host        = azurerm_public_ip.test-publicIP-VM[count.index].ip_address
timeout        = "2m"
}
provisioner "file" {
#connection = azurerm_linux_virtual_machine.test-linux.connection
source      = "${path.module}/WebContents/server-contents.html"
destination = "/var/www/html/index.nginx-debian.html"
}
triggers = {
timestamp = timestamp()
}
depends_on = [
azurerm_linux_virtual_machine.test-linux,
azurerm_network_interface.test-nic,
azurerm_public_ip.test-publicIP-VM,
data.azurerm_public_ip.publicip
]
}

I have tried to use data to pass the IP address but I still get and error. This is the link that I used: https://stackoverflow.com/questions/71292185/error-host-for-provisioner-cannot-be-emptyhost for provisioner cannot be empty

The error that I am encountering is this:
Error: remote-exec provisioner error
host for provisioner cannot be empty

To obtain the IP address of the network interface associated with each virtual machine, use the data azurerm_network_interface block.

I made below changes to your code.

data "azurerm_network_interface"  "test-nic" {
 count = var.vm_count 
 name = azurerm_network_interface.test-nic[count.index].name } 
resource "null_resource"  "default-web-server" { 
count = var.vm_count 
provisioner "remote-exec" { 
inline = [ 
"sudo apt-get update", 
"sudo apt-get install -y nginx", 
"sudo mkdir -p /var/www/html/", 
"sudo chown -R ${var.admin-user}:${var.admin-user} /var/www/html/", 
"sudo chmod 644 /var/www/html/index.nginx-debian.html" 
] 
} 
connection { 
type = "ssh" 
user = var.admin-user 
private_key = file("${path.module}/connection/linux-xxxx.pem") 
host = data.azurerm_network_interface.test-nic[count.index].private_ip_address 
timeout = "2m" 
} 
provisioner "file" { 
source = "xxxx" 
destination = "xxxx" 
} 
triggers = { 
timestamp = timestamp() 
} 
depends_on = [ azurerm_linux_virtual_machine.test-linux, azurerm_network_interface.test-nic, azurerm_public_ip.test-publicIP-VM, data.azurerm_public_ip.publicip ] }

After making these changes, I was able to successfully initialize terraform with a valid configuration.

If still the issue persists,

Calling ssh from local-exec might help in fixing by allowing you to provide additional connection parameters to the output.

Refer terraform hashicorp issues & Provisioners terraform for more relevant information.

And this is an intermittent issue as per the github issues.

I was able to fix my issues by using the public_ip_address parameter of the azurerm_virtual machine:

host = data.azurerm_virtual_machine.test-linux[count.index].public_ip_address

data "azurerm_virtual_machine" "test-linux" {
count = var.vm_count
name = azurerm_linux_virtual_machine.test-linux[count.index].name
resource_group_name = azurerm_resource_group.test-rg-nginx.name
}