Microsoft announces the general availability of custom metrics for rolling upgrades on Azure Virtual Machine Scale Sets. This new feature enables precise control over upgrade sequences, skipping specific VMs, and seamless integration with existing upgrade policies, enhancing upgrade flexibility and reliability. Unique :
Microsoft Rolls Out Custom Metrics for VM Scale Sets Rolling Upgrades
Microsoft just announced the general availability of custom metrics for rolling upgrades on Virtual Machine Scale Sets (VMSS). This new feature lets you fine-tune your upgrade process based on real-time application health data. For cloud architects and DevOps pros, this means smarter, safer, and more flexible upgrade workflows.
What’s New?
The key innovation here is the integration of the Application Health Extension with VMSS upgrades. It emits custom metrics that control the upgrade sequence and behavior. You can now:
- Control upgrade order: Define the exact sequence in which your VMs get upgraded.
- Skip specific instances: Exclude certain VMs from upgrades without affecting the rest.
- Seamless integration: Works smoothly with rolling upgrade policies, automatic OS and extension upgrades, and MaxSurge.
How Does It Work?
The upgrade process is organized into phases, which are logical groups of VMs within your scale set. Each phase is tagged via custom metrics sent by the Application Health Extension. VMSS uses this metadata to assign VMs to phases and then upgrades them in batches based on update domains, fault domains, and zone info.
Another cool feature is skip upgrade. This lets you exclude individual VM instances from upgrades dynamically. Unlike instance protection, it ties directly into your application logic and upgrade workflow. When a rolling upgrade starts, VMSS checks if a VM’s custom metric has skipUpgrade set to true and skips it accordingly.
Why It Matters
This update is a game-changer for managing large-scale VM deployments. It gives you granular control over upgrades, reducing downtime and risk. Plus, it supports complex scenarios where some VMs need to stay untouched temporarily.
“Custom metrics for rolling upgrades empower you to tailor upgrade workflows based on real-time app health,” says Micah McKittrick from Microsoft.
“Skip upgrade integrates more seamlessly into rolling upgrades than instance protection, supporting instance-level application logic,” McKittrick adds.
Availability and Next Steps
The feature is now live in all public Azure regions. If you’re running VM Scale Sets, it’s worth exploring how custom metrics can optimize your upgrade strategy. Check out Microsoft’s official docs to get started.
In short, this update brings smarter automation and flexibility to VMSS upgrades, making your cloud infrastructure more resilient and easier to manage.
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