We usually scale out of the application by adding website instances for Azure websites.
Understanding of Service plan below. Kindly refer MSDN link for more details and decide which will work for your project need.
Free service plan will have only one instance created for your website and you can’t change the instances. Free service doesn’t provide auto-scaling as well.
Shared plan will have option to add up to six instances and provides auto scaling.
Standard plan will have option to add up to ten instances with full CPU resources available based on scale up option.
I would suggest to start with shared plan and then upgrade based on your project need.
By default ARR Affinity is enabled on your Azure App Service.
Also read: Storage Analytics Data Retention Policy in Microsoft Azure
If you increase the instances of your Azure app service to more than one, still it will be redirected to the same instance for each request.
But user needs to be distributed among all the instances and that’s the performance will be better.
We will have to play around with web.config and set the arr-disable-session-affinity value as true.
This will make the work done and user request will be routed among all the instances.
Hope this will be helpful.