Can I log to separate files using Serilog?

Question

My ASP.NET Core 2.1 app logs to a Serilog file sink, all the "usual stuff" - i.e. app related stuff such as debug, monitoring, performance, etc.

However we also need to log other data to a separate file. Not app related, but customer related - the kind of stuff that should go into a database. However for legacy reasons, there is no database on this system and so that data needs to be saved to a file instead. Obviously this can't be written to the same log file.

I could just write to a FileStream. But I prefer to do structured logging with Serilog.

So is there a way to have two loggers simultaneously? Which log different data to different file sinks.

(If so, how do I inject them into my classes - right now I just inject ILogger<ClassName>.)

Answer 1

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.