How do you access the built IHost's service provider after Build() to resolve services outside the normal request/injection flow, such as in Program.cs itself?

Intermediate

Answer

After calling builder.Build(), the resulting IHost exposes a Services property (an IServiceProvider) that Program.cs or other top-level startup code can use to resolve services directly -- commonly used for running one-time startup logic like applying database migrations or seeding initial data before calling host.Run().

var host = builder.Build();

using (var scope = host.Services.CreateScope()) {
    var db = scope.ServiceProvider.GetRequiredService<AppDbContext>();
    await db.Database.MigrateAsync();  // one-time startup migration
}

host.Run();

Real-world example A Worker Service's Program.cs resolves a scoped DbContext once at startup (via a manually created scope) to apply pending EF Core migrations automatically before the application begins processing any background work.

Common follow-ups: Why is a manually created scope needed here instead of just calling GetRequiredService directly on host.Services?;What are the risks of running migrations automatically at every startup versus as a separate deployment step?

Entity Framework Core & Data Access;Dependency Injection

All 15 Generic Host questions