How to make Serilog pick up both the expression template and a console (color) theme from appsettings.json

Question

I'm trying to configure Serilog for my ASP.NET app using appsettings.json and am following the instructions from the GitHub Serilog.Settings.Configuration project readme. I cannot get the Console output format expression working from appsettings.json when I also set a theme. When both are configured directly in code it works just fine.

This is the Serilog section of appsettings.json. Note the full template is more complex, it uses Substring(SourceContext, LastIndexOf(SourceContext, '.') + 1) amonst others, but this is how I am testing for now:

{
  "Serilog": {
    "MinimumLevel": {
      "Default": "Information",
      "Override": {
        "Microsoft.AspNetCore": "Warning",
        "Microsoft.EntityFrameworkCore.Database.Command": "Warning"
      }
    },
    "WriteTo": [
      {
        "Name": "Console",
        "Args": {
          "formatter": {
            "type": "Serilog.Templates.ExpressionTemplate, Serilog.Expressions",
            "template": "[{@t:HH:mm:ss:fff} {@l:u3}]  {SourceContext,48} : {@m}\n{@x}"
          },
          "theme": "Serilog.Sinks.SystemConsole.Themes.AnsiConsoleTheme::Code, Serilog.Sinks.Console"
        }
      }
    ],
    "Enrich": [ "FromLogContext" ]
  }
}

And this is the resulting output (with theme colors):

[17:13:38 INF] Configure
[17:13:38 INF] Now listening on: https://localhost:5001
[17:13:38 INF] Now listening on: http://localhost:5000
[17:13:38 INF] Application started. Press Ctrl+C to shut down.

Which appears to be the default format (note the msec field in the timestamp and the Source Context field are missing).

When I omit the theme setting from the json, the output looks like this, i.e. with the correct expression template applied (e.g. source context) but without any color:

[17:13:37:498 INF]                            App.Web.Server.Program : Server started
[17:13:37:797 INF]                            App.Web.Server.Startup : ConfigureServices

This is the same format I get when I configure the logger in code, but then I get the theme color too!

I also tried to use this format from the project's samples:

          "WriteTo": [
            {
              "Name": "Console",
              "Args": {
                "outputTemplate": "[{Timestamp:HH:mm:ss} {SourceContext} [{Level}] {Message}{NewLine}{Exception}",
                "theme": "Serilog.Sinks.SystemConsole.Themes.SystemConsoleTheme::Grayscale, Serilog.Sinks.Console"
              }
            }
          ]

This is without the format expression, just the format (and a slight variation on the format itself) and, as expected, results in:

[14:35:11 Microsoft.Hosting.Lifetime [Information] Now listening on: "https://localhost:5001"
[14:35:11 Microsoft.Hosting.Lifetime [Information] Now listening on: "http://localhost:5000"

I tried umpteen variations and combinations without any success. So it seems that using appsettings.json I can either get the expression template working, or the theme working, but not both at the same time.

Again: when configured directly in code it "just works" ...

Suggestion are welcome.

Answer 1

I tried as below:

Packages:

in appsettings.json:

"Serilog": {
    "MinimumLevel": {
      "Default": "Information",
      "Override": {
        "Microsoft.AspNetCore": "Warning",
        "Microsoft.EntityFrameworkCore.Database.Command": "Warning"
      }
    },
    "WriteTo": [
      {
        "Name": "Console",
        "Args": {
          "theme": "Serilog.Sinks.SystemConsole.Themes.AnsiConsoleTheme::Code, Serilog.Sinks.Console",
          "outputTemplate": "Time:{Timestamp: HH:mm:ss.fff} Level:{Level} DetailedInfo:{Message}{NewLine}{Exception}"
        }
      }
    ],
    "Enrich": ["FromLogContext"]
  }

In program.cs:

public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                })
                .UseSerilog((context, logger) =>
                {
                    logger.ReadFrom.Configuration(context.Configuration);
                    

                });

Result: and with

"theme": "Serilog.Sinks.SystemConsole.Themes.SystemConsoleTheme::Grayscale, Serilog.Sinks.Console"