Creating High-Availability Virtual Machines on Azure

In the world of enterprise cloud architecture, uptime is everything. When designing solutions for clients across Latin America, one request I encounter constantly is: "How do we ensure our application stays online even if a data center fails?"

The answer lies in understanding the difference between Azure Availability Sets and Availability Zones. In this guide, I'll walk you through how to architect a solution that offers a 99.99% SLA using Terraform.

The 99.99% SLA Requirement

Microsoft offers different Service Level Agreements (SLAs) depending on how you deploy your VMs. A single VM with Premium SSD storage gives you 99.9%. But to reach the gold standard of 99.99%, you must deploy across multiple Availability Zones.

Implementation with Terraform

Manual configuration in the portal is prone to human error. Here is the exact Terraform module structure I use to provision zoned VMs for my clients.

resource "azurerm_linux_virtual_machine" "main" {
  name                = "prod-vm-web-01"
  resource_group_name = azurerm_resource_group.example.name
  location            = azurerm_resource_group.example.location
  size                = "Standard_D2s_v3"
  admin_username      = "adminuser"
  
  # CRITICAL: Define the specific zone
  zone                = "1" 

  network_interface_ids = [
    azurerm_network_interface.example.id,
  ]

  os_disk {
    caching              = "ReadWrite"
    storage_account_type = "Premium_LRS"
  }

  source_image_reference {
    publisher = "Canonical"
    offer     = "UbuntuServer"
    sku       = "18.04-LTS"
    version   = "latest"
  }
}

Notice the `zone` parameter. To achieve high availability, you would loop this resource creation to deploy a secondary VM in `zone = "2"` and place both behind a Standard Load Balancer.

Validating the Architecture

Once deployed, you can verify the distribution using the Azure CLI. I’ve written a custom Bash script that checks the zonal status of all VMs in a resource group.

Conclusion

Designing for failure is the hallmark of a Senior Cloud Architect. By leveraging Availability Zones and automating the deployment with Terraform, you ensure your client's infrastructure is robust, compliant, and ready for scale.