HTTP Error 500.35 - ANCM Multiple In-Process Applications in same Process ASP.NET Core 3

Question

From this morning without any changes to the code of the project, a very simple Web API, one controller and 3 methods, with Swagger, it doesn\'t start anymore and I get the

Answer 1

I got the same error when I did the following:

1. Published two separate asp.net core websites
2. In IIS, created two websites under "Default Web Site", each having physical path set to each of the publish folders in (1) respectively.
3. Now whichever of the sites I open first works, and the second gives that error.

Problem:

Since both my sites are under "Default Web Site" they are both using DefaultAppPool, which is the cause of this error. The same error occurs when the sites are not under "Default Web Site" but use the same app pool.

Solution:

As mentioned in the docs,

To fix this error, run apps in separate IIS application pools.

for me this problem was resolved when I started using separate app pools for each site.