sample exception generator to test NLog exception logging

IndentExceptionLayoutRenderer.cs

using NLog;
using NLog.LayoutRenderers;
using System;
using System.Linq;
using System.Text;
using System.Collections.Concurrent;

namespace NLogTest
{
	/// <summary>
	/// renders exception starting from new line
	/// with short type exception name followed by message
	/// and stacktrace (optionally)
	/// if exception is logged more than once (catched, logged and re-thrown as inner), stack trace is not written
	/// </summary>
	[LayoutRenderer("IndentException")]
	public class IndentExceptionLayoutRenderer : LayoutRenderer
	{
		/// <summary>
		/// indent before exception type (default is tab)
		/// </summary>
		public string Indent { get; set; }
		/// <summary>
		/// indent between each stack trace line (default is two tab characters)
		/// </summary>
		public string StackTraceIndent { get; set; }
		/// <summary>
		/// is written before exception type name (default [)
		/// </summary>
		public string BeforeType { get; set; }
		/// <summary>
		/// is written after exception type name (default ])
		/// </summary>
		public string AfterType { get; set; }
		/// <summary>
		/// separator between exception type and message
		/// </summary>
		public string Separator { get; set; }
		/// <summary>
		/// log stack trace or not (for console logger e.g.)
		/// </summary>
		public bool LogStack { get; set; }

		/// <summary>
		/// holds logged already exceptions just to skip surplus stack logging
		/// </summary>
		static ConcurrentQueue<Exception> _loggedErrors = new ConcurrentQueue<Exception>();

		public IndentExceptionLayoutRenderer()
		{
			Indent = "\t";
			StackTraceIndent = "\t\t";
			BeforeType = "[";
			AfterType = "]";
			LogStack = true;
			Separator = " ";
		}

		protected override void Append(StringBuilder builder, LogEventInfo logEvent)
		{
			var e = logEvent.Exception;
			while (e != null)
			{
				builder.AppendFormat("{1}{2}{0}{3}{4}", e.GetType().Name, Indent, BeforeType, AfterType, Separator);
				builder.Append(e.Message);

				if (LogStack)
				{
					var stackTraceWasLogged = _loggedErrors.Contains(e);
					if (!stackTraceWasLogged)
					{
						builder.AppendLine();
						_loggedErrors.Enqueue(e);
						builder.AppendFormat("{0}", e.StackTrace.Replace("   ", StackTraceIndent));
					}

					if (_loggedErrors.Count > 50)
					{
						_loggedErrors.TryDequeue(out Exception ex1);
						_loggedErrors.TryDequeue(out Exception ex2);
					}
				}

				e = e.InnerException;
				if (e != null)
					builder.AppendLine();
			}
		}
	}
}

NLog.config

<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://www.nlog-project.org/schemas/NLog.xsd NLog.xsd"
      autoReload="true"
      throwExceptions="false"
      internalLogLevel="Off" internalLogFile="%temp%\nlog-internal.log">

  <!-- optional, add some variables
  https://github.com/nlog/NLog/wiki/Configuration-file#variables
  -->
  <variable name="logfilename" value="NLogTest"/>


	<targets>
	<target xsi:type="ColoredConsole"
					name="console"
					useDefaultRowHighlightingRules="true"
					detectConsoleAvailable="true"
			layout="${message}${onexception:${newline}${exception:maxInnerExceptionLevel=10:format=shortType,message}}" />
	
		<target name="file" xsi:type="File"
		fileName="${basedir}/${logfilename}.log"
		keepFileOpen="false"
layout="${longdate} ${logger} ${message}${onexception:${newline}${exception:maxInnerExceptionLevel=10:format=shortType,message,stacktrace:separator=*:innerExceptionSeparator=&#xD;&#xA;&#x9;}}" />

    
  </targets>

  <rules>
		<logger name="*" minlevel="Debug" writeTo="file" />
		<logger name="*" minlevel="Trace" writeTo="Console" />
	</rules>
</nlog>

NLog.exceptionIndent.config

	<target xsi:type="ColoredConsole"
					name="console"
					useDefaultRowHighlightingRules="true"
					detectConsoleAvailable="true"
			layout="${level} ${message}${onexception:${newline}${IndentException:LogStack=false:separator=&#x9;:beforeType=:aftertype=}}" />
	
		<target name="file" xsi:type="File"
		fileName="${basedir}/${logfilename}.log"
		keepFileOpen="false"
layout="[${threadid}] ${longdate} ${level} ${logger} ${message}${onexception:${newline}${IndentException}}" />

NLogTest.cs

using NLog;
using NLogTest.Classes;
using System;
using System.Collections.Generic;

namespace NLogTest
{
	class Program
	{
		static ILogger Log = LogManager.GetCurrentClassLogger();

		static void Main(string[] args)
		{
			Log.Debug("starting");
			try
			{
				new UnitOfWork().tryException();
			}
			catch (Exception e)
			{
				Log.Error(e, "failed to start NLogTest");
				Console.ReadKey();
			}
			Log.Debug("the end");
		}
	}
}

namespace NLogTest.Classes
{
	class UnitOfWork
	{
		static ILogger Log = LogManager.GetCurrentClassLogger();

		public void innerException()
		{
			throw new KeyNotFoundException("innerException");
		}

		public void outerException()
		{
			try
			{
				innerException();
			}
			catch (Exception e)
			{
				throw new ArgumentException("outer exception", e);
			}
		}

		public void tryException()
		{
			try
			{
				outerException();
			}
			catch (Exception e)
			{
				Log.Error(e, "tryException failure");
				throw new ArgumentException("bad try", e);
			}
		}

	}
}

I've asked a question about exception layout renderer at SO
However seems that writing custom layout renderer is not so complex
So here i will keep IndentExceptionLayoutRenderer.cs source code
This renderer allows to show exception using readable format (from my point of view) in the log (file or console)
NLog.exceptionIndent.config is a sample configuration that shows how layout can be parameterized for console and file logging