The deployment task isn't always easy, as there can be a number of issues (mostly depending on the server machine state) that can prevent it from going well. This statement is particularly true for ASP.NET Core application IIS-based deployments, as the reverse proxy mechanism undeniably adds an additional level of complexity.

Luckily enough, there are a lot of things we can do to diagnose the most common problems. Here are the most relevant ones:

1. Read the browser output messages, optionally setting the ASPNETCORE_ENVIRONMENT variable to Development to print out the stack trace and/or the exception(s) details.
2. Examine the Windows Event Viewer's application log.
3. Enable the ASP.NET Core module stdout logging feature.
4. Try to reproduce the error(s) on Kestrel.

Let's see each one of them in detail.