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This article discusses how to troubleshoot a scenario in which Windows Server node pools don't get upgraded automatically from Gen1 to Gen2 virtual machines (VMs) when a cluster node image is upgraded in Microsoft Azure Kubernetes Service (AKS).
Note
This scenario doesn't apply to Gen2 VMs on Linux node pools.
Prerequisites
- Azure CLI version 2.0.81 or later. See Install Azure CLI for installation instructions.
Symptoms
Existing Windows Server node pools don't get upgraded from Gen1 to Gen2 when you upgrade the node image by using one of the following methods in Azure CLI:
An entire cluster upgrade (by using the
az aks upgradecommand)A specific node pool upgrade (by using the
az aks nodepool upgradecommand)
Cause
Cause 1: Existing node pools aren't automatically upgraded to Gen2 VMs
By design, a node image upgrade doesn't support updating or upgrading existing node pools. The az aks upgrade and az aks nodepool upgrade commands upgrade only the node image (to a later node image version). These commands don't upgrade the corresponding VM generation.
Cause 2: Cluster upgrade to Kubernetes version 1.25 or a later version upgrades only the OS
When you upgrade your cluster to Kubernetes version 1.25 or a later version, only the operating system (OS) is upgraded (to Windows Server 2022). Existing node pools aren't affected. The associated Azure Virtual Machine Scale Sets contain VMs that have the same Gen1 VM.
Cause 3: Cluster upgraded and new node pool created by using Windows Server 2022 without specifying a valid VM size
After you upgrade the cluster to Kubernetes version 1.25 or a later version, you specify Windows Server 2022 as the OS to use on the node pool's VMs. However, the VMs don't use a Gen2 node image reference for one of the following reasons:
You don't specify a VM size, and the default VM size in the region doesn't support Gen2 VMs.
You specify a Gen1-only VM size.
When you upgrade the default OS from Windows Server 2019 (Windows2019) to Windows Server 2022 (Windows2022), the existing node pools aren't automatically upgraded to a different VM generation.
Solution
Upgrade the cluster, and then create a new Windows Server node pool that supports Gen2 VM sizes on that cluster according to the following guidelines.
| Kubernetes cluster upgrade version | Cluster creation guidelines |
|---|---|
| 1.25 or a later version | When you run the az aks create command to create a cluster, set the --node-vm-size parameter to a Gen2 VM size. |
| Any version earlier than 1.25 | When you run the az aks create command to create a cluster, set the --os-sku parameter value to Windows2022, and set the --node-vm-size parameter value to a Gen2 VM size. |
Note
If you specify a Gen2 VM size and set the operating system as Windows Server 2019, you receive an ErrorCode_Windows2019NotSupportedWithGen2VM error code that's accompanied by the following error message:
<virtual-machine-size> is a Gen 2-only VM. Windows2019 does not support Gen 2 VMs. However, you can select a Gen 1 VM size or set os_sku to 2022.
To avoid this problem, choose one of the following options when you create the cluster:
Pick a Gen1 VM size to use together with Windows Server 2019.
Set the operating system SKU to Windows Server 2022 to use together with your Gen2 VM.
Before you create a new node pool, verify that the VM size supports Gen2 VMs in your region. To do this, run
az vm list-sizes --___location <region> --query "[?contains(name, 'v2')].name" --output table.To verify the current and available node image versions, run the following commands:
- To check the current version:
az aks nodepool show --resource-group <resource-group> --cluster-name <cluster-name> --name <nodepool-name> --query nodeImageVersion - To check the latest available version:
az aks nodepool get-upgrades --resource-group <resource-group> --cluster-name <cluster-name> --nodepool-name <nodepool-name> --query latestNodeImageVersion
- To check the current version:
Contact us for help
If you have questions or need help, create a support request, or ask Azure community support. You can also submit product feedback to Azure feedback community.