Accessing logger when configuring app configurations in .NET Core generic host

Question

I have a .NET Core 3.1 application and I'm setting up the generic host as follows:

static void Main(string[] args)
{
    Host.CreateDefaultBuilder(args)
        .ConfigureLogging((context, loggingBuilder) =>
        {
            loggingBuilder.AddConsole();
            loggingBuilder.AddDebug();
        })
        .ConfigureAppConfiguration((context, configurationBuilder) =>
        {
            // I want to get an ILogger instance here, but how?
            configurationBuilder.Add(new CustomConfigurationSource(logger));
        })
        // some other setup logic
        .Build().Run();
}

The problem is that I want to use an ILogger when configuring app configurations. The configuration source I used needs to access a remote server, and also contains some complicated logic for configuration reload, so I want it to be able to write logs for diagnostic and monitoring purposes.

Is there any proper way that this can be done in .NET Core generic host? I would think that this is a pretty legit requirement but can't seem to figure out a way.

The same problem statement also applies to ASP.NET Core applications.

Brando Zhang · Accepted Answer · 2020-09-08 05:27:10Z

2

As far as I know, we couldn't access the Ilogger since the service hasn't been registered in CreateDefaultBuilder method.

If you want to use logger in the ConfigureAppConfiguration, I suggest you could try to create the logger by yourself.

Like below:

       Host.CreateDefaultBuilder(args)
 .ConfigureLogging((context, loggingBuilder) =>
 {
    
 })
 .ConfigureAppConfiguration((context, configurationBuilder) =>
 {
     using (var loggerFactory = LoggerFactory.Create(builder => builder.AddConsole()))
     {
 
      var logger =   loggerFactory.CreateLogger(typeof(Program));
     logger.LogInformation("Example log message");
      }
     // I want to get an ILogger instance here, but how?


 })
 // some other setup logic
 .Build().Run();

Result:

answered Sep 8, 2020 at 5:27

Brando Zhang

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1 Comment

scharnyw Over a year ago

Thanks! This seems to be the best workaround after I read through this GitHub issue. Feels like quite a limiting issue in generic host though

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