Autoscale up instance without traffic

Question

Using Standard S1 App Service plan for a web app & applied auto scaling. it's a testing web app, only few traffic is there, but sometime specially in night it is seen that it scale up to 3/4 instances, even after stopping the web app, sometime instance scale up to 2-3.

I set up auto-scaling rules, scale up when CPU utilization >70% & scale down when CPU utilization<20%.

I am not sure what that means. I would appreciate if you could please shed some light on this?

Thanks and Regards,

Jaswant

Answer 1

HI

what you have configured is  that if the cpu exceeds 70% the system increases the vm

if it falls below 20% it decreases them, however options may have been configured for which in particular periods the system follows other policies for example you can add scale conditions that are active on a given date and time, or that recur on a weekly basis.

Ref:

https://learn.microsoft.com/en-us/azure/azure-monitor/autoscale/autoscale-get-started#scale-based-on-a-repeating-schedule

Also take into consideration that when you create an app in App Service, it is put into an App Service plan. When the app runs, it runs on all the VM instances configured in the App Service plan. If multiple apps are in the same App Service plan, they all share the same VM instances. If you have multiple deployment slots for an app, all deployment slots also run on the same VM instances. If you enable diagnostic logs, perform backups, or run WebJobs, they also use CPU cycles and memory on these VM instances.In this way, the App Service plan is the scale unit of the App Service apps. If the plan is configured to run five VM instances, then all apps in the plan run on all five instances. If the plan is configured for autoscaling, then all apps in the plan are scaled out together based on the autoscale settings.

Ref:

https://learn.microsoft.com/en-us/azure/app-service/overview-hosting-plans

Cheers

Luca