How does one use Elmah in ASP.NET 5/vNext/Core?

Instead of using ELMAH, it's not hard to implement error logging manually. This process will catch any exception that occurs in the project and log it to a database table. To do this, add the following to the Configure method in Startup.cs

  if (env.IsDevelopment())
  {
    app.UseDeveloperExceptionPage();
    app.UseBrowserLink();
  }
  else
  {
    app.UseExceptionHandler(builder =>
      {
        builder.Run(async context =>
        {
          context.Response.StatusCode = (int)System.Net.HttpStatusCode.InternalServerError;
          context.Response.ContentType = "text/html";

          var error = context.Features.Get<Microsoft.AspNetCore.Diagnostics.IExceptionHandlerFeature>();
          if (error != null)
          {
            LogException(error.Error, context);
            await context.Response.WriteAsync("<h2>An error has occured in the website.</h2>").ConfigureAwait(false);
          }
        });
      });
  }

Include this in Startup.cs as well:

private void LogException(Exception error, HttpContext context)
{
  try
  {
    var connectionStr = Configuration["ConnectionString"];
    using (var connection = new System.Data.SqlClient.SqlConnection(connectionStr))
    {
      var command = connection.CreateCommand();
      command.CommandText = @"INSERT INTO ErrorLog (Application, Host, Type, Source, Path, Method, Message, StackTrace, [User],  WhenOccured)
    VALUES (@Application, @Host, @Type, @Source, @Path, @Method, @Message, @StackTrace, @User,  @WhenOccured)";
      connection.Open();

      if (error.InnerException != null)
        error = error.InnerException;

      command.Parameters.AddWithValue("@Application", this.GetType().Namespace);
      command.Parameters.AddWithValue("@Host", Environment.MachineName);
      command.Parameters.AddWithValue("@Type", error.GetType().FullName);
      command.Parameters.AddWithValue("@Source", error.Source);
      command.Parameters.AddWithValue("@Path", context.Request.Path.Value);
      command.Parameters.AddWithValue("@Method", context.Request.Method);
      command.Parameters.AddWithValue("@Message", error.Message);
      command.Parameters.AddWithValue("@StackTrace", error.StackTrace);
      var user = context.User.Identity?.Name;
      if (user == null)
        command.Parameters.AddWithValue("@User", DBNull.Value);
      else
        command.Parameters.AddWithValue("@User", user);
      command.Parameters.AddWithValue("@WhenOccured", DateTime.Now);

      command.ExecuteNonQuery();
    }
  }
  catch { }
}

Note that you will have to create a table in your database with the structure used in this function.

ELMAH hasn't been updated to support ASP.NET Core yet. Atif Aziz did some work building a web.config free configuration module called Bootstrapper. Bootstrapper doesn't support ASP.NET Core (as of my knowledge). But I'm pretty sure that work supporting the new version will start as soon as we get nearer to RTM.