Where can I log an ASP.NET Core app's start/stop/error events?

Question

In old ASP.NET, in the Global.asax.cs class, I would log when the app starts, stops and throws unhandled exceptions:

• Application_Start()
• Application_End()
• Application_Error()

How do I do the same in ASP.NET Core? It has a Startup class, but it is for configuration.

Where do I hook into the app's start/stop/error events?

Answer 1

Note: For .NET Core 3.0 or later, this answer is obsolete. See this answer instead.

You need to use Microsoft.AspNetCore.Hosting.IApplicationLifetime

    /// <summary>     /// Triggered when the application host has fully started and is about to wait     /// for a graceful shutdown.     /// </summary>     CancellationToken ApplicationStarted { get; }      /// <summary>     /// Triggered when the application host is performing a graceful shutdown.     /// Requests may still be in flight. Shutdown will block until this event completes.     /// </summary>     CancellationToken ApplicationStopping { get; }      /// <summary>     /// Triggered when the application host is performing a graceful shutdown.     /// All requests should be complete at this point. Shutdown will block     /// until this event completes.     /// </summary>     CancellationToken ApplicationStopped { get; } 

Instance of IApplicationLifetime could be obtained in Configure method. Also add ILoggerFactory here:

public void Configure(IApplicationBuilder app, IApplicationLifetime applicationLifetime, ILoggerFactory loggerFactory) {     // use applicationLifetime } 

Having ILoggerFactory, you can create instance of ILogger:

var logger = loggerFactory.CreateLogger("StartupLogger");  

So you just need to create a property in the Startup class to persist the instance of ILogger (or ILoggerFactory, if you would like to create different ligger instance for different events). To summarize:

public class Startup  {     private ILogger _logger;      public void Configure(IApplicationBuilder app, IApplicationLifetime applicationLifetime, ILoggerFactory loggerFactory)      {         applicationLifetime.ApplicationStopping.Register(OnShutdown);         ...          // add logger providers         // loggerFactory.AddConsole()         ...         _logger = loggerFactory.CreateLogger("StartupLogger");     }      private void OnShutdown()     {          // use _logger here;     } }