How does VMSS predictive autoscaling works? I enabled it but no automatic scale out happed even after 15 days when predictive chart starts showing data

Question

How does VMSS predictive autoscaling works? I enabled it but no automatic scale out happed even after 15 days when predictive chart starts showing data

Pranshul G 40

Hi Team,

Azure VMSS is unable to scale out automatic when predictive auto is enabled and Average Percentage CPU is much higher compared to value shown in Predictive chart.

How does it actually work, Do i need to set a static thershold after reviwing predicitve chart?

Thanks

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Pranshul G 40 Reputation points

2025-07-09T17:00:15.85+00:00

Hi Nikhil

Thanks for your response but in my case predictive auto scale didn't work , Kindly look into the screenshots I attached, I produced CPU spike (within blue circle) to validate predictive auto scale but nothing happened even after 20 min of continuous CPU spike.
Nikhil Duserla 8,515 Reputation points Microsoft External Staff Moderator

2025-07-09T17:05:24.2366667+00:00

Hello @Pranshul G,

Thank you for your response. Have you configured a threshold? If so, what is the threshold value? Also, what type of scaling have you selected—automatic or manual?
Pranshul G 40 Reputation points

2025-07-09T17:17:19.7333333+00:00
Hi @Nikhil Duserla

Yes, Following configuration enabled for Predictive Autoscale. It worked only when VM crossed Scale Out threshold but ideally new VM should have been trigered much before reaching the static scale out condition because Percentage CPU (AVG) was already much higher (but less than static value) as compared to predicted "Percentage CPU(avg)"

Custom Autoscale

Predictive autoscale = Enabled

Accepted answer

3 additional answers

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Pranshul G 40 Reputation points

2025-07-09T17:00:15.85+00:00

Hi Nikhil

Thanks for your response but in my case predictive auto scale didn't work , Kindly look into the screenshots I attached, I produced CPU spike (within blue circle) to validate predictive auto scale but nothing happened even after 20 min of continuous CPU spike.
Nikhil Duserla 8,515 Reputation points Microsoft External Staff Moderator

2025-07-09T17:05:24.2366667+00:00

Hello @Pranshul G,

Thank you for your response. Have you configured a threshold? If so, what is the threshold value? Also, what type of scaling have you selected—automatic or manual?
Pranshul G 40 Reputation points

2025-07-09T17:17:19.7333333+00:00

Hi @Nikhil Duserla

Yes, Following configuration enabled for Predictive Autoscale. It worked only when VM crossed Scale Out threshold but ideally new VM should have been trigered much before reaching the static scale out condition because Percentage CPU (AVG) was already much higher (but less than static value) as compared to predicted "Percentage CPU(avg)"

Custom Autoscale

Predictive autoscale = Enabled

Answer 1

Hello @Pranshul G,

Thank you for your time on call. To enable predictive autoscale, create a scale out rule based on 'Percentage CPU' metric. Click here to go to the 'Configure' tab to set an autoscale rule. User's image

This message means you attempted to enable predictive autoscale before you enabled standard autoscale and set it up to use the Percentage CPU metric with the Average aggregation type.

Please follow this link for more detailed information- https://learn.microsoft.com/en-us/azure/azure-monitor/autoscale/autoscale-predictive#didnt-enable-standard-autoscale

If you have any further queries, do let us know.

If you found this informative, please consider accepting an answer as a token of appreciation. And don't forget to give it a thumbs up 👍 if it was helpful.

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Answer 2

Hello @Pranshul G,An Azure Virtual Machine Scale Set can increase or decrease the number of virtual machines that run your application. Instance count can be updated in several ways:

Manually increasing or decreasing scale set capacity
Based on a set schedule
According to rules based on metrics thresholds
Automatically based on usage patterns discovered by predictive artificial intelligence

To set a static threshold for Azure VMSS predictive auto-scaling, navigate to the Scaling tab of your Virtual Machine Scale Set in the Azure portal. From there, you can configure manual scaling settings and adjust the thresholds according to your requirements-https://learn.microsoft.com/en-us/azure/virtual-machine-scale-sets/virtual-machine-scale-sets-autoscale-portal#prerequisites

Once the threshold value is configured and CPU utilization reaches that threshold, the instance will automatically scale out.

If you have any further queries, do let us know.

Answer 3

Pranshul G 40

Hi @Nikhil Duserla

Yes, Following configuration enabled for Predictive Autoscale. It worked only when VM crossed Scale Out threshold but ideally new VM should have been trigered much before reaching the static scale out condition because Percentage CPU (AVG) was already much higher (but less than static value) as compared to predicted "Percentage CPU(avg)"

Custom Autoscale
Predictive autoscale = Enabled

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Pranshul G 40 Reputation points

2025-07-09T17:17:40.94+00:00
@Nikhil Duserla If you don't mind can we connect over zoom so i can understand it from you?
Nikhil Duserla 8,515 Reputation points Microsoft External Staff Moderator

2025-07-09T17:27:11.73+00:00

Hello @Pranshul G,

Please continue this discussion in private message.

Answer 4

Pranshul G 40

To all community members for better clearity :

Predictive auto scale doesn't scale out itself, it provides you Percentage CPU (avg) predictaion based on that you can configure your VM resources and set standard scale out rule.

However, I am bit dissapointed why they named it as "predictive autoscale" when similar to this can be achieved via a simple reproting tool after analyzing few weeks data.

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How does VMSS predictive autoscaling works? I enabled it but no automatic scale out happed even after 15 days when predictive chart starts showing data

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