Asp.net core 3.1 webapi iis 8 not able to connect to sql server - asp.net-core-webapi

Question

I have asp.net core 3.1 web api. When I run the project locally in Visual studio, it works fine. But when I publish it to IIS and run it, I get the error.
500 Internal Server Error","error": "A connection was successfully established with the server, but then an error occurred during the pre-login handshake. (provider: TCP Provider, error: 0 - An existing connection was forcibly closed by the remote host.)"}
Or Login failed for user domain_name\machine_name.
connection string looks like this
"ConnectionStrings": {
"ABCDB": "Server=xxx-test,80;Database=abc;Integrated Security=true;MultipleActiveResultSets=true;"
},
I have the hosting bundle installed for .net core 3.
my app runs under ApplicationPoolIdentity which is added to the database and has the permissions. My application pool is set to No Managed Code with ApplicationPoolIdentity.
The endpoints for the api which are not connecting to the database work just fine on published version but anything that is connecting to the database gives the error.
I referred to couple of links but hard luck.
https://www.loganfranken.com/blog/1345/why-your-web-application-cant-connect-to-sql-server/
IIS fails to pass windows credentials through to SQL Server for ASP.NET Core app
Why asp.net core app uses different user than AppPool identity for Windows Authentication when connecting to SQL Server?
Any help is appreciated.
Edit: The only things that works for me running the appPool under custom account(my credentialis) but does not work under appPoolIdentity on IIS

Answer 1

It seem that your environment needs a reset.
1- Manually check your app folder under IIS to see if any cached files or similar ones could be deleted.
2- Ideally, install it in a new folder under IIS
3- Reset the IIS
4- Make a hard refresh of the web browser

Answer 2

your connection string should be like this:
"ABCDB": "Data Source=xxx-test;Initial Catalog=abc;Integrated Security=SSPI;Persist Security Info=True;"
and add application pool name of your published application of security/users folder of your DB:
IIS APPPOOL\<apppool name>
Or add a new user account to you DB with user name and password. In this case you will also have to change the connection string.

Answer 3

I was having the same issue.
Other .NET Core 3.1 web apps are running just fine with the same authentication method (anonymous authentication) on the same IIS instance on the same server using the same connection string to the same MS SQL DB.
With this one particular .NET Core 3.1 web app, IIS is causing the app to try to authenticate to MSSQL DB with the username {DOMAIN}\{Computer Name}
The issue for me was that the connection string for the one app with the issue had "Trusted_Connection=True".
I knew that I would get this authentication interception from IIS with Integrated_Security but did not realize that Integrated_Security is synonymous with Trusted_Connection.
So the fix is to remove Trusted_Connection = True or Integrated_Security = True from the DB connection string in the app. If you need either of these two for your code to work (but are providing a username and password in the DB connection string), you should probably re-evaluate your code. Otherwise, the behavior OP and I observed should be what you want to happen and this isn't a problem.