As per my knowledge, Azure VM allows user to do in-place scaling up and down with Reserved Instance (RI) offer (1/2/3 yrs).
If I have an App Service with Premium plan, and Azure Advisor service gives me recommendation to use RI, how do I use the reserved instance offer for 1/2/3 years? Can I just scale down App Service plan to availa the new pricing from App service left navigation panel and just select the new plan or same plan with RI offer? Because I am unable to do this in-place scaling down to use RI for my existing App Service plan in my Dev/Test or Prod environments.
Or do I have to recreate my App Service plan infrastructure from scratch again to use RI offer of Premium or Isolated plan?
The important thing to know about Reserved Instances in Azure is that
The reserved instance pricing applies to the applicable instances in your subscription, up to the number of instances that you reserve. The reserved instances are a billing matter and are not tied to specific compute instances
So if you reserve 2 instances, then each billing period will have the cost of up to 2 instances deducted. If you are running 3 matching instances, the cost for 2 will be deducted. If you are running 1 matching instance, the cost for 1 will be deducted.