Virtual network integration in App Service previously required one subnet per App Service plan integration. If you are working with many App Service plans, managing the subnets can be an unnecessary administrative task. Therefore, we are happy to announce the general availability of multi plan subnet join (MPSJ).
MPSJ reduces subnet sprawl when dealing with many apps across many plans and simplifies management of networking control such as Network Security Groups and Route tables across App Service plans.
With MPSJ you can join a virtual network/subnet in a different subscription, but all App Service plans joining a specific subnet must be in the same subscription.
Learn more.