I had problem in connection between SQL server and IIS. I found this Q/A . The accepted solution says that IIS APPPOOL\YourAppPoolName
should be granted to the SQL server. However I have added a login to SQL server with name NT Authority/IUSR
and in user mapping I mapped this login to the desired database and it works.
What is the difference between ApplicationPoolIdentity and IUSR identity? Is there any security or performance difference between IUSR or APPPOOL?