This is a Serilog Sink for Grafana's new Loki Log Aggregator.

What is Loki?

Loki is a horizontally-scalable, highly-available, multi-tenant log aggregation system inspired by Prometheus. It is designed to be very cost effective and easy to operate, as it does not index the contents of the logs, but rather a set of labels for each log stream.

You can find more information about what Loki is over on Grafana's website here.

• Formats and batches log entries to Loki via HTTP
• Ability to provide global Loki log labels
• Comes baked with an HTTP client, but your own can be provided
• Works witn Serilog.Settings.Configuration package

Coming soon:

• Ability to provide contextual log labels
• Write logs to disk in the correct format to send via Promtail
• Send logs to Loki via HTTP using Snappy compression

The Adeptik.Serilog.Sinks.Loki NuGet package can be found here. Alternatively you can install it via one of the following commands below:

NuGet command:

Install-Package Adeptik.Serilog.Sinks.Loki

.NET Core CLI:

dotnet add package Adeptik.Serilog.Sinks.Loki

var credentials = new LokiCredentials("http://localhost:3100"); // Address to local or remote Loki server with no auth
// or var credentials = new LokiCredentials("http://localhost:3100", "login", "pass"); for basic auth

Log.Logger = new LoggerConfiguration()
        .MinimumLevel.Information()
        .Enrich.FromLogContext()
        .WriteTo.LokiHttp(credentials)
        .CreateLogger();

var exception = new {Message = ex.Message, StackTrace = ex.StackTrace};
Log.Error(exception);

var position = new { Latitude = 25, Longitude = 134 };
var elapsedMs = 34;
Log.Information("Message processed {@Position} in {Elapsed:000} ms.", position, elapsedMs);

Log.CloseAndFlush();

Loki indexes and groups log streams using labels, in Adeptik.Serilog.Sinks.Loki you can attach labels to all log entries by passing an list of labels to the WriteTo.LokiHttp(..) configuration method. This is ideal for labels such as instance IDs, environments and application names:

var labels = new List<LokiLabel>
{
    new LokiLabel("app", "demo"),
    new LokiLabel("namespace", "prod")
};

var credentials = new LokiCredentials("http://localhost:3100");

var logger = new LoggerConfiguration()
        .MinimumLevel.Verbose()
        .Enrich.FromLogContext()
        .WriteTo.LokiHttp(credentials, labels)
        .CreateLogger();

In some occasions you'll want to add labels to your log stream within a particular class or method, this feature isn't quite finished yet but will be available soon.

Adeptik.Serilog.Loki.Sink is built on top of the popular Serilog.Sinks.Http library to post log entries to Loki. With this in mind you can you can extend the default HttpClient (LokiHttpClient), or replace it entirely by implementing IHttpClient.

// ExampleHttpClient.cs

public class ExampleHttpClient : LokiHttpClient
{
    public override Task<HttpResponseMessage> PostAsync(string requestUri, HttpContent content)
    {
        return base.PostAsync(requestUri, content);
    }
}

// Usage

var credentials = new BasicAuthCredentials("http://localhost:3100", "<username>", "<password>");
var logger = new LoggerConfiguration()
        .MinimumLevel.Verbose()
        .Enrich.FromLogContext()
        .WriteTo.LokiHttp(credentials, labels, new ExampleHttpClient())
        .CreateLogger();

To use the console sink with Microsoft.Extensions.Configuration, for example with ASP.NET Core or .NET Core, use the Serilog.Settings.Configuration package.

Instead of configuring the sink directly in code, call ReadFrom.Configuration():

var configuration = new ConfigurationBuilder()
    .AddJsonFile("appsettings.json")
    .Build();

var logger = new LoggerConfiguration()
    .ReadFrom.Configuration(configuration)
    .CreateLogger();

In your appsettings.json file, under the Serilog node, :

{
  "Serilog": {
    "WriteTo": [
        {
            "Name": "LokiHttp",
            "Args": {
                "credentials": {
                    "Url": "http://192.168.43.30:3100",
                    "Username": "login",
                    "Password": "pass"
                },
                "logLabels": [
                    {
                        "Key": "app",
                        "Value": "demo"
                    },
                    {
                        "Key": "namespace",
                        "Value": "production"
                    }
                ]
            }
        }
    ]
  }
}

This package is still in its infancy so if there's anything missing then please feel free to raise a feature request, either that or pull requests are most welcome!