Azure App Service - ARR Affinity - Auto-scaling - Stateful application

Question

I would like to get details on the behavior of the app with ARR Affinity enabled and autoscaling?

Let's say I deploy a stateful ASP.NET web app on Azure Web App. Therefore I enable ARR Affinity. I configure autoscaling as well.

What happens if ever an instance is put down due to autoscaling. Does ARR Affinity prevent the scale in as long as user session is still active, or is the user session suddenly broken?

Could you please then give pieces of advice on how to configure stateful application in Azure Web App (or something else)?

Thank you!

Answer 1

Unfortunately if one of your instances is put down and the server is no longer availble, then all the requests corresponding to the ARR Affinity cookie will fail.

When you have stateful applications it is suggested to scale up instead of scale out. Meaning instead of creating multiple instances of your application, one should increase the resources given in the current instance by upgrading tier.

You can find a really nice and explanatory post from a Microsoft Expert (this is a legit tag) in Microsoft forum here