Can I log to separate files using Serilog?

The simplest way I've managed to do this was to implement a new unique interface that I could pass to the DI system to be consumed by the controllers.
Note: In the example I used the Serilog.Sinks.RollingFile NuGet package. Use any other sinks as you see fit. I use asp.net Core 2.1.

New Interface

using Serilog;
using Serilog.Core;

public interface ICustomLogger
{
    ILogger Log { get; }
}

public class CustomLogger : ICustomLogger
{
    private readonly Logger _logger;

    public ILogger Log { get { return _logger; } }

    public CustomLogger( Logger logger )
    {
        _logger = logger;
    }
}

Implementation in Startup.cs

using Serilog;
...
public void ConfigureServices( IServiceCollection services )
{
    ...

    ICustomLogger customLogger = new CustomLogger( new LoggerConfiguration()
        .MinimumLevel.Debug()
        .WriteTo.RollingFile( @"Logs\CustomLog.{Date}.log", retainedFileCountLimit: 7 )
        .CreateLogger() );
    services.AddSingleton( customLogger );

    ...
}

Usage in Controller

public class MyTestController : Controller
{
    private readonly ICustomLogger _customLogger;

    public MyTestController( ICustomLogger customLogger )
    {
        _customLogger = customLogger;
    }

    public IActionResult Index()
    {
        ...
        _customLogger.Log.Debug( "Serving Index" );
        ...
    }
}

You can definitely do that.

1. You need to import package Serilog.Sinks.File

2. Then you have to configure Serilog.

   In program.cs do following thing.

   Log.Logger = new LoggerConfiguration()
           .MinimumLevel.Debug()
           .MinimumLevel.Override("Microsoft", LogEventLevel.Information)
           .Enrich.FromLogContext()
       .WriteTo.File(
           @"<<your log file path>>",
       fileSizeLimitBytes: 10000000,
       rollOnFileSizeLimit: true,
       shared: true,
       flushToDiskInterval: TimeSpan.FromSeconds(1))
           .CreateLogger();
   

In buildWebHost function add UseSerilog().

public static IWebHost BuildWebHost(string[] args) =>
    WebHost.CreateDefaultBuilder(args)
    .UseStartup<Startup>()
        .UseSerilog() // <-- Add this line
        .Build();

Update 1

I have used EventId property. This is just demo that how you can use different file based on eventId but for your requirement you have to implement additional thing your own.

Program.cs

public class Program
    {
        public static void Main(string[] args)
        {
            Log.Logger = new LoggerConfiguration()
                .WriteTo.Logger(cc => cc.Filter.ByIncludingOnly(WithProperty("EventId",1001)).WriteTo.File("Test1001.txt",flushToDiskInterval: TimeSpan.FromSeconds(1)))
                .WriteTo.Logger(cc => cc.Filter.ByIncludingOnly(WithProperty("EventId", 2001)).WriteTo.File("Test2001.txt", flushToDiskInterval: TimeSpan.FromSeconds(1)))
                .CreateLogger();

            CreateWebHostBuilder(args).Build().Run();
        }

        public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
            WebHost.CreateDefaultBuilder(args).UseSerilog()
                .UseStartup<Startup>();

        public static Func<LogEvent, bool> WithProperty(string propertyName, object scalarValue)
        {
            if (propertyName == null) throw new ArgumentNullException("propertyName");           
            ScalarValue scalar = new ScalarValue(scalarValue);
            return e=>
            {
                LogEventPropertyValue propertyValue;
                if (e.Properties.TryGetValue(propertyName, out propertyValue))
                {
                    var stValue = propertyValue as StructureValue;
                    if (stValue != null)
                    {
                        var value = stValue.Properties.Where(cc => cc.Name == "Id").FirstOrDefault();
                        bool result = scalar.Equals(value.Value);
                        return result;
                    }
                }
                return false;
            };
        }
    }

My HomeController.cs

  public class HomeController : Controller
    {
        ILogger<HomeController> logger;
        public HomeController(ILogger<HomeController> logger)
        {
            this.logger = logger;
        }
        public IActionResult Index()
        {
            logger.Log(LogLevel.Information,new EventId(1001), "This is test 1");
            logger.Log(LogLevel.Information, new EventId(2001), "This is test 2");
            return View();
        } 
    }

Note: Main thing is that you have to use some type of filter.

Serilog.Sinks.Map does this, and includes a file logging example:

Log.Logger = new LoggerConfiguration()
    .WriteTo.Map("EventId", "Other", (name, wt) => wt.File($"./logs/log-{name}.txt"))
    .CreateLogger();