NLog ApplicationInsightsTarget unable to read application insights key from appsettings.json - azure-application-insights

Question

I am trying to read the application insights instrumentation key from appsettings.json file in my ASP.NET Core 3.1 Web Application but all my tries went in vain so far as the target is still showing as unconfigured.
If I add the key directly in ApplicationInsightsTarget, then it is working fine.
Here is the content of appsettings.json file:
{
"Logging": {
"LogLevel": {
"Default": "Information",
"Microsoft": "Warning",
"Microsoft.Hosting.Lifetime": "Information"
}
},
"AllowedHosts": "*",
"AppInsightsKey": "Instrumentation-Key-From-Azure-Application-Insights-Resource"
}
Here is the content of nlog.config file:
<?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"
autoReload="true"
throwConfigExceptions="true"
internalLogLevel="info"
internalLogFile="c:\temp\internal-nlog-AspNetCore3.txt">
<!-- enable asp.net core layout renderers -->
<extensions>
<add assembly="Microsoft.ApplicationInsights.NLogTarget" />
<add assembly="NLog.Web.AspNetCore"/>
</extensions>
<!-- the targets to write to -->
<targets>
<!--Console Target for hosting lifetime messages to improve Docker / Visual Studio startup detection -->
<target xsi:type="Console" name="lifetimeConsole" layout="${configsetting:item=AppInsightsKey} ${level:truncate=4:lowercase=true}: ${logger}[0]${newline} ${message}${exception:format=tostring}" />
<target name="aiTarget" xsi:type="ApplicationInsightsTarget"
layout="${date:format=yyyy-MM-dd HH\:mm\:ss}: [LOCAL] - ${level} - ${message}${exception:format=ToString}">
<instrumentationKey>${configsetting:item=AppInsightsKey}</instrumentationKey>
<contextproperty name="threadid" layout="${threadid}" />
</target>
</targets>
<!-- rules to map from logger name to target -->
<rules>
<logger name="*" minlevel="Trace" writeTo="lifetimeConsole" />
<logger name="*" minlevel="Trace" writeTo="aiTarget" />
</rules>
</nlog>
As you can see from above, I was trying to grab the application insights key from appsettings.json file by ${configsetting:item=AppInsightsKey}, but in all occasions it's coming as empty.
I've tried with ${configsetting:name=AppInsightsKey} , which didn't help either.
This is the program.cs file content
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using NLog.Web;
using System;
namespace ASPNETCoreWebAppNLogAppInsightsDemo
{
public class Program
{
public static void Main(string[] args)
{
var logger = NLog.Web.NLogBuilder.ConfigureNLog("nlog.config").GetCurrentClassLogger();
try
{
logger.Debug("init main");
CreateHostBuilder(args).Build().Run();
}
catch (Exception exception)
{
//NLog: catch setup errors
logger.Error(exception, "Stopped program because of exception");
throw;
}
finally
{
// Ensure to flush and stop internal timers/threads before application-exit (Avoid segmentation fault on Linux)
NLog.LogManager.Shutdown();
}
}
public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.ConfigureWebHostDefaults(webBuilder =>
{
webBuilder.UseStartup<Startup>();
})
.ConfigureLogging(logging =>
{
logging.ClearProviders();
logging.SetMinimumLevel(Microsoft.Extensions.Logging.LogLevel.Trace);
})
.UseNLog(); // NLog: Setup NLog for Dependency injection
}
}
Then I've tried to embed the key in the console target layout, just to ensure nlog is able to read it correctly, which to my surprise is working perfectly fine. So, looks like the issue is with ApplicationInsightsTarget only.
I know, I can pull it from Environment variables and hence in Azure App service it is not required to read from appsettings.json, but I would like to understand about this behavior since already spent too much time fixing myself :-)
Any help will be appreciated.

Answer 1

Try replacing the old code:
var logger = NLogBuilder.ConfigureNLog("nlog.config").GetCurrentClassLogger();
With this new code:
var logger = LogManager.Setup()
.LoadConfigurationFromAppSettings()
.GetCurrentClassLogger();
The new code will load the appsettings.json, and sure that ${configsetting} are available during initialization of NLog Targets.