Set Log Levels for Microsoft.* , System, and AspNet when using Serilog

I had always imagined that

  "Logging": {
    "LogLevel": {
      "Default": "Debug",
      "System": "Information",
      "Microsoft": "Information"
    }
  },

would set my project code's log level to Debug, and make Microsoft.* namespaces log at Information level or higher. It seems not. With this config, AspNetCore infrastructure logs at Debug level.

How do I target Microsoft.* to not use the Default level?

I'm using Serilog, but the injected Loggers are all Microsoft.Extensions.Logging.ILogger so I expected Microsoft.Extensions.Logging config to kick in.

Is this a mistaken assumption?

Yes, the assumption that Serilog will respect the Logging.LogLevel section when used with Extensions.Logging is wrong. It doesn't.

To read serilog levels from config, some options are:

• use https://github.com/serilog/serilog-settings-configuration and use the config structure they give, especially the section at MinimumLevel, LevelSwitches, overrides like this:

  "Serilog": {
    "MinimumLevel": {
      "Default": "Information",
      "Override": {
        "MyStuff.ThatsStillWorkInProgress": "Verbose",
        "MyStuff.ThatsOldAndWellTested": "Information",
        "Microsoft": "Warning",
        "Microsoft.AspNetCore.Hosting": "Information",
        "Microsoft.AspNetCore.Hosting.Diagnostics": "Debug",
        "Microsoft.Hosting.Lifetime": "Information",
        "Microsoft.AspNetCore.SignalR": "Information",        
        "System": "Warning",
        "System.Net": "Error"
      }
    },
    "WriteTo": [
      {
        "Name": "File",
        "Args": {
          "Path": "../logs/log-%COMPUTERNAME%-.txt",
          "rollingInterval": "Day"
        }
      }
    ]
  },

• For those who do Serilog config in code, use something like this:

var defaultLogLevel = configuration.GetLogLevel("Default");
var aspNetCoreLogLevel = configuration.GetLogLevel("Microsoft.AspNetCore");
var microsoftLogLevel = configuration.GetLogLevel("Microsoft");
var logger = new LoggerConfiguration()
                .MinimumLevel.Is(defaultLogLevel)
                .MinimumLevel.Override("Microsoft.AspNetCore", aspNetCoreLogLevel)
                .MinimumLevel.Override("Microsoft", microsoftLogLevel)
                // ... etc ...

// ...

static LogEventLevel GetLogLevel(this IConfiguration configuration, string @namespace, string fallbackLevel = "Information")
{
        return Enum.Parse<LogEventLevel>(configuration["Logging:LogLevel:" + @namespace] ?? fallbackLevel);
}

Other Points

• Using appSettings.json for minimum levels has the advantage that you can make use of reloadOnChange.
• Don't forget Serilog uses Verbose where Extensions.Logging uses Trace