Creating a Serilog Custom Enricher

Serilog is a popular logging library for .NET that provides a flexible and extensible way to log messages from applications. One of the key features of Serilog is the ability to enrich log events with additional contextual information that can help in troubleshooting and debugging.

In this blog post, we will explore how to create a custom enricher with Serilog to add custom properties to log events.

📢Development

To create a custom enricher with Serilog , we need to define a class that implements the ILogEventEnricher interface.

public interface ILogEventEnricher
{
    void Enrich(LogEvent logEvent, ILogEventPropertyFactory propertyFactory);
}

ILogEventEnricher.cs Interface

This interface contains a single method Enrich(LogEvent logEvent, ILogEventPropertyFactory propertyFactory) that we need to implement to add custom properties to log events.

Let's start by creating a new class called AspNetCoreEnvironmentEnricher that implements the ILogEventEnricher interface:

using Serilog.Core;
using Serilog.Events;
using System;

namespace Serilog.Labs.CustomEnrichers.Enrichers
{
    //class must implement interface ILogEventEnricher
    public class AspNetCoreEnvironmentEnricher : ILogEventEnricher
    {
        static readonly string _aspNetEnvironment;

        /// <summary>
        /// static constructor to load the environment variable
        /// </summary>
        static AspNetCoreEnvironmentEnricher()
        {
            _aspNetEnvironment = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");
        }

        public void Enrich(
            LogEvent logEvent, 
            ILogEventPropertyFactory propertyFactory)
        {
            var enrichProperty = propertyFactory
                .CreateProperty(
                    "AspNetCoreEnvironment", 
                    _aspNetEnvironment);

            logEvent.AddOrUpdateProperty(enrichProperty);
        }
    }
}

AspNetCoreEnvironmentEnricher.cs implementation

The Enrich method is called for each log event, and we can use it to add custom properties to the logEvent parameter. The propertyFactory parameter can be used to create new properties that we can add to the log event.

Using AspNetCoreEnvironmentEnricher

Now that we have our custom enricher class, let's use it with Serilog. We can add it to the logger configuration like this:

Log.Logger = new LoggerConfiguration()
    .Enrich.With(new AspNetCoreEnvironmentEnricher())
    .WriteTo.Console(
        outputTemplate: "[{AspNetCoreEnvironment} {Level:u3}] {Message:lj}{NewLine}{Exception}")
    .CreateLogger();

Using the AspNetCoreEnvironmentEnricher

In this example, we added our custom enricher to the logger configuration using the Enrich.With method. We passed the current user's name "Alice" to the constructor of our enricher.

Now, when we log a message, the UserName property will be added to the log event:

Log.Information("Hello, world!");

/*Will Output
[Information Development] Hello, world!
*/

😎Conclusion

Creating a custom enricher with Serilog is a simple and powerful way to add contextual information to log events.

By implementing the ILogEventEnricher interface and using the propertyFactory parameter, we can add any custom properties we need to help in troubleshooting and debugging our applications.