A couple of extension methods for adding log4net support to ASP.NET 5. This currently only supports dnx451 (full .NET framework) as log4net does not have CoreCLR support yet.

Inside of project.json, add a reference to dotnetliberty.AspNet.log4net:

{
  "webroot": "wwwroot",
  "userSecretsId": "aspnet5-AspNet5Log4Net-96932d2b-063c-4568-a826-82f718a33f40",
  "version": "1.0.0-*",

  "dependencies": {
    // ... 
    "dotnetliberty.AspNet.log4net": "1.0.0-beta8"
  },

With ASP.NET 5 we no longer have a web.config file. Instead we should create an XML file at the root of our project that contains just our log4net configuration. For example:

Notice that we are using a pattern for the file name. The value of the property appRoot is provided at runtime by this library.

<?xml version="1.0" encoding="utf-8" ?>
<log4net>
  <appender name="RollingFile" type="log4net.Appender.FileAppender">
    <file type="log4net.Util.PatternString" value="%property{appRoot}\app.log" />
    <layout type="log4net.Layout.PatternLayout">
      <conversionPattern value="%-5p %d{hh:mm:ss} %message%newline" />
    </layout>
  </appender>

  <root>
    <level value="DEBUG" />
    <appender-ref ref="RollingFile" />
  </root>
</log4net>

Add an extra line in the Startup.cs constructor to tell it where to find the log4net XML file:

public class Startup
{
    public Startup(IHostingEnvironment env, IApplicationEnvironment appEnv)
    {
        // Setup configuration sources.

        var builder = new ConfigurationBuilder()
            .SetBasePath(appEnv.ApplicationBasePath)
            .AddJsonFile("appsettings.json")
            .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true);

        appEnv.ConfigureLog4Net("log4net.xml");

        // ...
    }
    // ...

Make a call to loggerFactory.AddLog4Net inside of the Configure method in Startup.cs.

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    loggerFactory.MinimumLevel = LogLevel.Verbose;
    loggerFactory.AddConsole();
    loggerFactory.AddDebug();

    loggerFactory.AddLog4Net();
    // ...

Now you will be able to use the Microsoft Logging framework throughout your application, and log4net will be used as a logging provider (based on the configuration provided in log4net.xml).

var logger = loggerFactory.CreateLogger("Test");
logger.LogInformation("This will get written to app.log via log4net.");