Serilog Setup With Seq

Seq is built for modern structured logging with message templates. It allows us to search and filter logs with SQL-style queries. If you don’t have paid subscription, you can run Seq on your local machine with Docker. You can use Serilog.Sinks.Seq to send logs to Seq with Serilog. This tutorial will show you how to set it up for your Asp.Net Core application.

Getting started with Docker

If you are new to Docker, follow the quick start document to set it up on your machine. Then you can follow this article to set up Seq as a local Docker instance. Alternatively, if you know Terraform, you can use this Terraform script to provision a Docker instance.

If everything goes well, you can visit Seq UI with http://localhost:5341.

Set up Asp.Net Core

First install the following packages: Serilog.AspNetCore, Serilog.Sinks.Seq, and Serilog.Exceptions.

Then update Program.cs to use Serilog:

public class Program
{
    public static void Main(string[] args)
    {
        var environment = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");

        var configuration = new ConfigurationBuilder()
            .AddJsonFile("appsettings.json")
            .AddJsonFile($"appsettings.{environment}.json", true)
            .Build();

        Log.Logger = new LoggerConfiguration()
            .ReadFrom.Configuration(configuration)
            .CreateLogger();

        try
        {
            Log.Information("Starting web host");
            CreateHostBuilder(args).Build().Run();
        }
        catch (Exception e)
        {
            Log.Fatal(e, "Host terminated unexpectedly");
        }
        finally
        {
            Log.CloseAndFlush();
        }
    }

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

It reads Serilog configuration from app settings.

Lastly, add Serilog app settings:

{
  "Serilog": {
    "Using": [ "Serilog.Sinks.Seq" ],
    "MinimumLevel": {
      "Default": "Debug",
      "Override": {
        "Microsoft": "Information"
      }
    },
    "WriteTo": [
      {
        "Name": "Seq",
        "Args": {
          "serverUrl": "http://localhost:5341"
        }
      }
    ],
    "Enrich": [
      "WithExceptionDetails"
    ]
  }
}

Message Templates

Message Templates is a specification for capturing and rendering structured logs. Instead of logging a text message, it logs the message template with properties. It then allows you to search against the properties.

For example, you can log an exception in Asp.Net Core, like this:

var exception = new Exception("Engine error");
exception.Data["ErrorNo"] = 1;
_logger.LogError(exception, "Car crashed {Name}", "Apple");

The raw log in Seq looks like:

{
    "@t": "2020-09-07T21:16:34.7050951+12:00",
    "@mt": "Car crashed {Name}",
    "@m": "Car crashed Apple",
    "@i": "9bb3256d",
    "@l": "Error",
    "@x": "System.Exception: Engine error",
    "Name": "Apple",
    "SourceContext": "Garage.SerilogSeqSetup.Controllers.LogsController",
    "ActionId": "5a4daf50-a42f-426c-823b-38e65ee9fcaf",
    "ActionName": "Garage.SerilogSeqSetup.Controllers.LogsController.Get (Garage.SerilogSeqSetup)",
    "RequestId": "80000050-0007-ff00-b63f-84710c7967bb",
    "RequestPath": "/logs",
    "SpanId": "|246beaa6-4555748038f06ade.",
    "TraceId": "246beaa6-4555748038f06ade",
    "ParentId": "",
    "ExceptionDetail": {
        "Type": "System.Exception",
        "Data": {
            "ErrorNo": 1
        },
        "HResult": -2146233088,
        "Message": "Engine error",
        "Source": null
    }
}

You can easily find all logs related to the same name or exception type.

Demo

See Garage.SerilogSeqSetup.