ASP.NET Core 3.0 – Logging in the Startup Class (with NLog)

With ASP.NET Core 3.0, the ability to inject an ILogger or ILoggerFactory into the Startup class has been removed, so we can no longer do this:

I understand why this has been done, because creating a temporary DI container just for the startup process adds a lot of complexity and potential for errors.

However, my ConfigureServices method (and the new ConfigureContainer method added in 3.0) does quite a bit of work, including loading extension assemblies; I want to be able to log during that time.

I also want to make sure I only pass around the ILogger from the Microsoft.Extensions.Logging namespace to other objects used at startup.

The Workaround

I use NLog for my logging (https://nlog-project.org/). In my Program’s Main method I configure it like so:

You can grab details on how to create an nlog.config file from the NLog docs, I won’t go into it here.

Then, in my Startup class, I can create the NLogLoggerProvider class (this is sort of a factory for creating the Microsoft ILogger instances), and from that I can get my logger instance:

Hey presto, logging in the Startup class. Note that we are obviously outside the entire DI system for this logging (which is sort of the point).

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