Allow minimal host to be created without default HostBuilder behavior

[davidfowl]

Background and Motivation

The default host builder pulls in a ton of dependencies that are rooted for trimming by default. We should have a mode where the minimal host is dependency minimal as well.

These numbers are native AOT net8.0 compiled on linx-x64:

1. WebApplication.CreateBuilder() = 18.7 MB
2. With prototype changes of the proposed API - 12.9 MB

We can stick to the current naming convention and use the existing Create/CreateBuilder methods as the one with the defaults and CreateEmptyBuilder to be the empty one:

Proposed API

namespace Microsoft.AspNetCore.Builder
{
    public class WebApplication
    {
       public static WebApplication Create(string[] args);
       public static WebApplicationBuilder CreateBuilder();
       public static WebApplicationBuilder CreateBuilder(string[] args);
       public static WebApplicationBuilder CreateBuilder(WebApplicationOptions options);
+      public static WebApplicationBuilder CreateEmptyBuilder();
+      public static WebApplicationBuilder CreateEmptyBuilder(string[] args);
+      public static WebApplicationBuilder CreateEmptyBuilder(WebApplicationOptions options);
    }
}

namespace  Microsoft.Extensions.Hosting
{
    public class GenericHostWebHostBuilderExtensions
    {
       public static IHostBuilder ConfigureWebHost(this IHostBuilder builder, Action<IWebHostBuilder> configure)
       public static IHostBuilder ConfigureWebHost(this IHostBuilder builder, Action<IWebHostBuilder> configure, Action<WebHostBuilderOptions> configureWebHostBuilder)
+      public static IHostBuilder ConfigureEmptyWebHost(this IHostBuilder builder, Action<IWebHostBuilder> configure, Action<WebHostBuilderOptions> configureWebHostBuilder)
    }
}

API Usage

WebApplicationBuilder builder = WebApplication.CreateEmptyBuilder();
builder.Logging.AddConsole();

WebApplication app = builder.Build();

app.MapGet("/", () => "Hello World");

app.Run();

Features

When creating an "empty" web application, the following features will be on (✅) or off (❌) by default. Note that these features can be enabled by the app explicitly after creating the builder/application. They just won't be enabled by default, in order to reduce app size.

• Features
  • StaticWebAssets ❌
  • IHostingStartup ❌
• Configuration
  • command line args ✅
  • appsetttings.json ❌
  • User secrets ❌
  • env variables ✅
• Middleware
  • Routing ✅
  • Auth ❌
  • HostFiltering ❌
  • ForwardedHeaders ❌
• Logging
  • Logging configuration support ❌
  • ConsoleLogger ❌
  • DebugLogger ❌
  • EventSourceLogger ❌
• Servers
  • IIS in proc ❌
  • IIS out of proc ❌
  • Kestrel
    • HTTP 1 ✅
    • HTTPS ❌
    • HTTP 2 ❌
    • HTTP 3 ❌

Alternative Designs

We could create whole new class names for another type of "Application" than a "WebApplication". Something like:

var apiBuilder = ApiApplication.CreateBuilder(args);
var apiApp = builder.Builder();

Other possible names include:

• HttpApplication
• ContainerApplication
• CloudApplication
• WorkerApplication

Risks

Potential confusion about which one to call. The template should make it obvious that the "empty" builder doesn't have anything in it, and you need to add things like appsettings, console logging, etc.

[Pilchie]

4 and 5 appear to be the same config above?

[davidfowl]

Fixed

Thanks for contacting us.

We're moving this issue to the Next sprint planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[pranavkm]

API review will tolerate CreateEmptyBuilder as an API here given the goals here.

[webczat]

I am one of the people who would still like it, so +1! also I'm for CreateBuilder vs CreateBuilderWithDefaults or something like that, because it explicitly says what's the intention here without the confusion. Considering that the WebApplication api is not yet in any stable version of aspnetcore, it's still open for such changes, isn't it?
CreareBuilder vs CreateEmptyBuilder looks more confusing by name.

[webczat]

also my non trimming usecase is: for example I would like to create a local webapp, the one that listens on localhost and it makes no sense for it to be exposed or have a reverse proxy in front or actually even have most of the config knops or files. And it would have config in some user profile directory. And things like that. I don't need things like the iis integration, forwarded headers, etc, even for the theoretical future, so I would prefer not to bring all these.
Other stuff although it's just personal preference and can likely be done with non empty builder, I do not necessarily want the default logging and kestrel sections to be named "Logging" and "Kestrel". And to be fair, in case of the app I mentioned, maybe I don't want them at all at least the Kestrel one. There is limited utility in setting up kestrel to do anything beyond listening to localhost in this case. Even urls are a bit too much because exposing that would be super dangerous. But that's likely not a problem.

[davidfowl]

@DamianEdwards suggested adding a boolean to the existing CreateBuilder API

[webczat]

well... could be. I am not even sure my first idea wasn't like that :) but I'd be okay with such a bool.

[DamianEdwards]

What I suggested:

namespace Microsoft.AspNetCore.Builder
{
    public partial class WebApplication
    {
+       public static WebApplicationBuilder CreateBuilder(string[] args = null); // Calls overload below with useDefaults=true
+       public static WebApplicationBuilder CreateBuilder(bool useDefaults, string[] args = null);
    }
}

[webczat]

what about only one overload and useDefaults as an optional parameter set to true by default? Is that even acceptable? considering it doesn't have to be compatible with anything...