# Evaluate a Spot Priority Mix change during scaling, not immediately after saving

> Why can the existing standard-to-Spot population remain unchanged after a mix-policy update?

- Canonical URL: https://update.dsesecurity.com/updates/dse-20260909-386-evaluate-a-spot-priority-mix-change-during-scaling-not-immediately-after-saving/
- Publisher: Detection Systems & Engineering (DSE Security)
- Author: DSE Security Editorial Team
- Published: 2026-09-10T00:25:30+00:00
- Modified: 2026-09-10T02:01:56+00:00
- Last reviewed by DSE: 2026-09-09
- Resource type: Guide
- DSE priority: Information
- Topics: Business Continuity, IT
- Reading time: 2 minutes

## What you need to know

Why can the existing standard-to-Spot population remain unchanged after a mix-policy update?

## Potentially affected

Azure Flexible scale sets already configured for Spot Priority Mix.

## DSE recommendation

Separate acceptance of the saved mix policy from acceptance of its effect during an approved scale operation.

## Article

## Source facts

Spot Priority Mix is available for Flexible, not Uniform, scale sets. Its base count defines the standard-VM portion below the distribution threshold; the percentage setting applies to capacity above that base. Updating those settings does not immediately create, delete, or rebalance existing VMs. The new distribution is applied during subsequent scaling operations. Portal updates are limited to scale sets where the feature is already enabled. [Microsoft Learn](https://learn.microsoft.com/en-us/azure/virtual-machine-scale-sets/spot-priority-mix).

## Applicability

Use this distinction when a saved policy and current instance inventory appear inconsistent. Record the total population, priority of each instance, and actual scaling events since the change. Do not infer a failed update simply because a static population still reflects the previous settings.

## DSE recommendation

Separate acceptance of the saved mix policy from acceptance of its effect during an approved scale operation. Have the workload owner define the intended standard baseline and the distribution above it. Keep that design decision separate from any immediate need to restore application capacity. Avoid repeatedly editing the same percentage in an attempt to force an undocumented instant rebalance.

## Verification

Confirm the saved policy first. Then, during an authorized scaling test, compare the before-and-after instance priorities and the operation result with the intended distribution. Record any eviction and distinguish running instances from the inventory being counted. If no qualifying scale operation has occurred, leave population convergence unverified rather than claiming either success or failure from the saved settings alone.

## Official references

[Microsoft Learn: Spot Priority Mix](https://learn.microsoft.com/en-us/azure/virtual-machine-scale-sets/spot-priority-mix). Source reviewed September 9, 2026.

## Primary reference

- Name: Get high availability and cost savings with Spot Priority Mix for Virtual Machine Scale Sets - Azure Virtual Machine Scale Sets | Microsoft Learn
- Authority: Microsoft Learn
- URL: https://learn.microsoft.com/en-us/azure/virtual-machine-scale-sets/spot-priority-mix
- Source publication date: Not stated by the source

## Citation and use

Preferred citation: “Evaluate a Spot Priority Mix change during scaling, not immediately after saving,” DSE Security, https://update.dsesecurity.com/updates/dse-20260909-386-evaluate-a-spot-priority-mix-change-during-scaling-not-immediately-after-saving/
Publishing principles: https://update.dsesecurity.com/updates/dse-updates-editorial-methodology/
Usage and citation policy: https://update.dsesecurity.com/usage/
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