How to Change VM Generation in Azure?

Changing the VM generation in Azure, specifically from Generation 1 (Gen1) to Generation 2 (Gen2), is not an in-place conversion but rather a migration process that involves creating new Gen2 virtual machines and transferring the workload. This migration allows you to leverage the enhanced capabilities and performance benefits offered by Gen2 VMs.

Understanding Azure VM Generations

Azure offers two types of VM generations, each built on different hardware architectures and firmware:

• Generation 1 (Gen1) VMs: These VMs utilize BIOS-based architecture and support older operating systems. They are suitable for a wide range of workloads but have certain limitations compared to Gen2.
• Generation 2 (Gen2) VMs: These VMs are based on UEFI firmware architecture, providing improved boot times, enhanced security features like Secure Boot, and support for larger memory configurations and OS disks (up to 2 TB for OS disks). They are generally recommended for modern operating systems and demanding workloads.

Why Migrate to Generation 2 VMs?

Migrating to Gen2 VMs offers several advantages:

• Enhanced Security: UEFI firmware and Secure Boot help protect against boot-time malware.
• Improved Performance: Faster boot times and better overall performance for certain workloads.
• Increased Scalability: Support for larger OS disks (up to 2 TB) and potentially larger memory configurations.
• Modern Features: Access to newer hardware capabilities and functionalities.

The Migration Process: Step-by-Step

The process of changing a VM's generation in Azure involves a series of careful steps to ensure data integrity and minimal downtime.

Step 1: Plan and Prepare

Before initiating the migration, it's crucial to plan thoroughly:

• Assess Compatibility: Ensure your operating system and applications are compatible with Gen2 VMs. Windows Server 2012 and later, and most recent Linux distributions, support Gen2.
• Understand Differences: Familiarize yourself with the key differences between Gen1 and Gen2 VMs, especially regarding boot processes and supported features.
• Choose VM Size: Select an appropriate Gen2 VM size that meets your workload's requirements. Not all VM sizes support Gen2.

Step 2: Ensure Data Protection

Crucially, before making any changes, ensure that you have valid and up-to-date backups of your existing Gen1 VMs, including both OS disks and data disks. This serves as your recovery point in case of any unforeseen issues during the migration. Azure Backup is a robust solution for this.

Step 3: Create a Gen2-Compatible OS Disk (from Gen1)

Since you cannot directly convert a Gen1 OS disk to a Gen2 OS disk, you need to prepare your Gen1 OS disk to be used with a new Gen2 VM.

1. Generalize the Gen1 VM: If your Gen1 VM is running Windows, generalize it using Sysprep to remove machine-specific information. For Linux, ensure agent and network configurations are ready for a new VM.
2. Capture an Image: Create a managed image from your generalized Gen1 VM's OS disk. This image will be used as the source for your new Gen2 VM's OS disk. Alternatively, you can take a snapshot of the OS disk and create a new managed disk from it.

Step 4: Provision New Gen2 VMs

Now, you will create a new virtual machine using the Gen2 architecture.

1. Create a New VM: In the Azure portal, select "Create a resource" > "Virtual machine."
2. Select Generation 2: During the VM creation process, choose Generation 2 under the "Advanced" or "VM Generation" option.
3. Use Your Image/Disk: When configuring the OS disk, select the managed image you created in Step 3. This will provision a new Gen2-compatible OS disk for your new VM.

Step 5: Attach Data Disks

After the new Gen2 VM is provisioned and its OS disk is ready:

1. Detach Data Disks (Optional): If your Gen1 VM is still running, detach its data disks (not OS disk) to ensure they are not in use.
2. Attach to New Gen2 VM: Attach the original data disks (or copies restored from your backup) to the newly created Gen2 VM. Ensure that disk drive letters are assigned correctly and applications can access their data.

Step 6: Validate and Test

This is a critical step to ensure a successful migration.

1. Boot the Gen2 VM: Start your new Gen2 VM.
2. Verify Functionality: Log in and thoroughly test all applications, services, and network connectivity.
3. Data Integrity Check: Confirm that all data on both OS and data disks is accessible and intact.
4. Performance Baseline: Compare performance metrics with your old Gen1 VM to ensure expected improvements or at least no regressions.

Step 7: Decommission Old Gen1 VMs (Optional)

Once you have confirmed that your new Gen2 VM is fully functional and stable, and all applications are running as expected, you can safely decommission the old Gen1 VM.

1. Stop and Deallocate: Stop and deallocate the Gen1 VM.
2. Delete Resources: Delete the Gen1 VM and its associated resources (disks, NICs) that are no longer needed. Ensure you only delete the old resources and not the new Gen2 resources.

Key Considerations for Migration

• Downtime: This migration process will incur downtime as you are switching from one VM to another. Plan for an appropriate maintenance window.
• IP Addresses: Decide if you want to retain the same public and private IP addresses. You might need to deallocate and reassign static IPs or update DNS records.
• Networking: Ensure that Network Security Groups (NSGs), Virtual Network (VNet) configurations, and any load balancers or application gateways are correctly configured for the new Gen2 VM.
• Automation: For multiple VMs, consider automating parts of this process using Azure PowerShell or Azure CLI scripts.

Gen1 vs. Gen2 VM Comparison

Here's a quick overview of the key differences:

Feature	Generation 1 (Gen1) VM	Generation 2 (Gen2) VM
Firmware	BIOS-based	UEFI-based
Boot Mode	MBR (Master Boot Record)	GPT (GUID Partition Table)
OS Disk Size	Up to 2 TB	Up to 2 TB for OS disk (larger for data disks)
Security	Basic boot security	Secure Boot, Trusted Launch (with compatible OS)
Supported OS	Broad range, including older Windows/Linux versions	Windows Server 2012+, recent Linux distributions
VM Sizes	Broad availability across all sizes	Specific sizes support Gen2 (e.g., v3/v4 series)
Performance	Standard	Potentially faster boot times and enhanced performance

By following these steps, you can successfully migrate your Azure virtual machines from Generation 1 to Generation 2, taking advantage of the latest platform capabilities.