How do I write logs from within Startup.cs?

Question

In order to debug a .NET Core app which is failing on startup, I would like to write logs from within the startup.cs file. I have logging setup within the file that can be u

Answer 1

None of the existing answers worked for me. I'm using NLog, and even building a new ServiceCollection, calling .CreateBuilder() on any service collection, creating a logging service ... none of that would write to a log file during ConfigureServices.

The problem is that logging isn't really a thing until after the ServiceCollection is built, and it's not built during ConfigureServices.

Basically, I just want (need) to log what's going on during startup in a configuration extension method, because the only tier I'm having a problem on is PROD, where I can't attach a debugger.

The solution that worked for me was using the old .NET Framework NLog method:

private static readonly NLog.Logger Logger = NLog.LogManager.GetCurrentClassLogger();

Added that right to the extension method class, and I was able to write to a log ("the" log) during ConfigureServices and after.

I have no idea if this is a good idea to actually release into production code (I don't know if the .NET controlled ILogger and this NLog.ILogger will conflict at any point), but I only needed it to see what was going on.