Unable to move app service to an existing app service plan

Many customers try to move app services to across resource groups, subscriptions or app service plan.

Under certain situation, moving app services to another app service plan is necessary. For example, density of app service is high. However, when changing app service plan, a common issue could occur - the existing app service plan is not found in the drop-down list.

This article will explain why it happens and will be helpful to get more insights of it.

Moving an app to another app service plan

We are able to simply change app service plan from Azure portal following steps in official document.
Manage App Service plan - Azure App Service | Microsoft Learn

Scenario

I have below resources

 - an app service: webapp-eastasia

 - a source app service plan: ASP-src

 - a destination app service plan: ASP-dst

 - 2 resource group: RG-1 and RG-2

I would like to change app webapp-eastasia from ASP-src to ASP-dst. According to official document, source plan and the target plan should be in the same resource group, geographical region.

Therefore, I ensure that 2 app service plans are both in the same resource group (RG-2), same subscription, same region (East Asia)

However, when changing app service plan from portal, the existing app service plan ASP-dst does not exist in the drop-down list. It only allows to create a new app service plan.

What cause this symptom

The reason is that source plan and target plan are in different webspace. Let's look deeper into the document.

App can only move between plans that are created in the same webspace. All plans created with the same resource group , region combination and operating system are deployed into the same webspace. That means, which webspace that plan is deployed to is determined once app service plan is created and webspace cannot be changed afterwards.

Let's see check the webspace of app service plan

Check webspace: Go to ASP -> JSON View

We could see that webspace of ASP-src is RG-1-EastAsiawebspace while ASP-dst is RG-2-EastAsiawebspace.

From these 2 webspaces, we could notice that prefix of the naming - one is RG-1-xxx and another one is RG-2-xxx.

That's because ASP-src was originally created in RG-1, then is moved to RG-2. And ASP-dst was created in RG-2.

Let's double confirm whether the resource group of ASP-src is indeed changed.

Check original resource group: Go to App service -> Diagnose and solve problems -> Configuration and Management-> Migration Options

Solution

Currently, the only solution is to move back to original resource group or create a new ASP.

Reference

Manage App Service plan - Azure App Service | Microsoft Learn

Moving an Azure App Service to another existing App Service Plan - Microsoft Q&A

Move Azure App Service resources across resource groups or subscriptions - Azure Resource Manager | Microsoft Learn