Are Flex mode orchestrated VMSS not eligible for Auto OS upgrade?

Question

I created a Flex orchestrated Azure VMSS with Ubuntu server image by canonical on M64 config. Trying to set this up for an Auto OS upgrade. After a thorough research seems like that is not feasible. I wanted to get some info on if my understanding is correct? Can someone provide inputs?

Answer 1

Hello Avanthika Sankararaman,

Welcome to the Microsoft Q&A and thank you for posting your questions here.

Problem

I understand that you are trying to enable automatic OS image upgrades on a Flexible Orchestration Azure VMSS with an Ubuntu server image. Through research, you found out some readings that suggest this feature is not supported for Flexible Orchestration VMSS and you would like to confirm and further clarify on this matter.

Solution

Your understanding is correct. Automatic OS image upgrades are not supported for Flexible Orchestration mode in Azure Virtual Machine Scale Sets (VMSS). This limitation applies specifically to VMSS instances that use flexible orchestration, which provides more advanced features and greater flexibility in how VMs are managed and scaled.

For more explanation: There are two types of Orchestration mode in this context which are Flexible Orchestration Mode and Uniform Orchestration Mode.

Flexible Orchestration in VMSS allows for more advanced deployment scenarios, such as mixed VM sizes and spot VMs. However, it does not support automatic OS image upgrades. This feature is only available for VMSS using Uniform Orchestration mode. In Uniform Orchestration, all VMs in the scale set are identical and automatic OS image upgrades are supported. Also, this mode ensures that all instances are updated consistently and is suitable for applications where uniformity and automatic updates are crucial.

To this extent, if you would like to use flexible orchestration and still want to manage OS upgrades, you will need to implement a custom solution such as:

• Create automation scripts using Azure CLI, PowerShell, or other tools to periodically check for updates and apply them to your VMs.
• Azure Update Management to schedule and manage OS updates for your VMs.
• Manually upgrade the OS image for your VMs by creating a new image version and updating the VMSS configuration to use the new image.

References

Source: Microsoft Learn on Automatic Guest Patching for Azure Virtual Machines and Scale Sets. Accessed, 7/13/2024.

Source: Azure Blog announcement on automatic OS upgrades for Azure VM scale sets. Accessed, 7/13/2024.

Also, kindly use the additional resources available by the right side of this page.

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Best Regards,

Sina Salam