Summary

This article discusses various methods to run code once the application starts in .Net6.

Abstract

The article "Run code once the application starts in .Net6" provides insights into executing code when an application starts in .Net6. It suggests two primary methods: writing code in the Program.cs file and using Hosted Services with the IHostedService interface. The Program.cs file allows code execution between builder.Services() for dependency registration or between app() for middleware configuration. Hosted Services, typically used for long-running background tasks, have StartAsync and StopAsync methods executed when the application starts and stops. Additionally, the article mentions using IHostApplicationLifetime events, such as ApplicationStarted, ApplicationStopping, and ApplicationStopped, to register callbacks.

Opinions

The author assumes the reader is a developer who may need to log something, populate data in memory, run background tasks, publish an event, or read configuration when the application starts.
The author suggests that the StartAsync method in Hosted Services should return quickly to avoid blocking other hosted services.
The author emphasizes that the OnStarted event is published after the application host has fully started, including services and request processing pipeline configuration, and the app has started serving web requests.
The author recommends trying out an AI service that offers similar performance and functions to ChatGPT Plus(GPT-4) but at a more cost-effective price of $6/month (Special offer for$ 1/month).

Run code once the application starts in .Net6

Maybe you need to execute some code once the application starts. Like log something, if you are a developer, you may need to populate some data in memory, run background tasks, publish an event, or read configuration.

Program.cs File

The first thing you probably have in mind is to write code in the Program.cs file. The .Net6 ensures that these methods, and therefore the code placed in them, will only be executed when the application starts. The developer can run code in two ways, between the builder.Services(…) here will be all the registration of dependencies, or the code can be placed between the app.(…) like before or after middlewares.

Code from Hosted Services

The other way is to run the code from Hosted Services, with an IHostedService interface that has StartAsync and StopAsync methods executed when the application starts and stops. This interface is typically used to trigger long-running background tasks, but StartAsync itself must return quickly so as not to block other hosted services if any. Also, it would be good to know that the StartAsync method runs before configuring the application’s request pipelines.

Using IHostApplicationLifetime Events

The three properties, namely ApplicationStarted, ApplicationStopping, and ApplicationStopped allow you to register callbacks. This is done using the Register() method.

app.Lifetime.ApplicationStarted.Register(OnStarted);

app.Lifetime.ApplicationStopping.Register(OnStopping);

app.Lifetime.ApplicationStopped.Register(OnStopped);

void OnStarted()

Console.WriteLine("test001");

void OnStopping()

Console.WriteLine("test002");

void OnStopped()

Console.WriteLine("test003");

Important to note that the OnStarted event is published after the application host has fully started, that is after the services and request processing pipeline have been configured, and the app has started serving web requests.

.NET Generic Host in ASP.NET Core | Microsoft Docs