How to tell when a self-hosted ASP.NET Core application is ready to receive requests?

Question

I need to launch worker processes that communicate using ASP.NET Core Web API. I need to know when I can start sending requests to that process. The only options I see so far are to have the worker call the parent process API when it has finished configuring or poll the worker with an "are you alive" request.

Is there any built in mechanism for this? Any better patterns or designs?

Answer 1

In general, after the application is started successfully, you will be able to send request.

For Application Start event, you could try IHostApplicationLifetime in .net core 8.0, if you are using previous version, you could try IApplicationLifetime which will be obsolete in future version.

Here is a demo which is used to register event while application is started.

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddControllersWithViews().AddNewtonsoftJson();         
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IHostApplicationLifetime hostApplicationLifetime)
    {
        hostApplicationLifetime.ApplicationStarted.Register(() => {
            Console.WriteLine("Application is Started");
        });

        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseExceptionHandler("/Home/Error");
            // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
            app.UseHsts();
        }
        app.UseHttpsRedirection();
        app.UseStaticFiles();

        app.UseRouting();        

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllerRoute(
                name: "default",
                pattern: "{controller=Home}/{action=Index}/{id?}");
        });
    }
}