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

Option 1: Directly use log (e.g. Serilog) in startup-

public class Startup
{
    public Startup(IHostingEnvironment env)
    {
        Log.Logger = new LoggerConfiguration()
           .MinimumLevel.Debug()
           .WriteTo.RollingFile(Path.Combine(env.ContentRootPath, "Serilog-{Date}.txt"))
           .CreateLogger();

        Log.Information("Inside Startup ctor");
        ....
    }

    public void ConfigureServices(IServiceCollection services)
    {
        Log.Information("ConfigureServices");
        ....
    }

    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        Log.Information("Configure");
        ....
    }

Output:

To setup Serilog in asp.net-core application, check out the Serilog.AspNetCore package on GitHub.

---

Option2: Configure logging in program.cs like this-

var host = new WebHostBuilder()
            .UseKestrel()
            .ConfigureServices(s => {
                s.AddSingleton();
            })
            .ConfigureLogging(f => f.AddConsole(LogLevel.Debug))
            .UseStartup()
            .Build();

host.Run();

User loggerFactory in startup like this-

public class Startup
{
    ILogger _logger;
    IFormatter _formatter;
    public Startup(ILoggerFactory loggerFactory, IFormatter formatter)
    {
        _logger = loggerFactory.CreateLogger();
        _formatter = formatter;
    }

    public void ConfigureServices(IServiceCollection services)
    {
        _logger.LogDebug($"Total Services Initially: {services.Count}");

        // register services
        //services.AddSingleton();
    }

    public void Configure(IApplicationBuilder app, IFormatter formatter)
    {
        // note: can request IFormatter here as well as via constructor
        _logger.LogDebug("Configure() started...");
        app.Run(async (context) => await context.Response.WriteAsync(_formatter.Format("Hi!")));
        _logger.LogDebug("Configure() complete.");
    }
}

Complete details available on this link