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Use ASP.NET Core with HTTP/2 on IIS

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By Justin Kotalik

HTTP/2 is supported with ASP.NET Core in the following IIS deployment scenarios:

  • Windows Server 2016 or later / Windows 10 or later
  • IIS 10 or later
  • TLS 1.2 or later connection
  • When hosting out-of-process: Public-facing edge server connections use HTTP/2, but the reverse proxy connection to the Kestrel server uses HTTP/1.1.

For an in-process deployment when an HTTP/2 connection is established, HttpRequest.Protocol reports HTTP/2. For an out-of-process deployment when an HTTP/2 connection is established, HttpRequest.Protocol reports HTTP/1.1.

For more information on the in-process and out-of-process hosting models, see ASP.NET Core Module (ANCM) for IIS.

HTTP/2 is enabled by default for HTTPS/TLS connections. Connections fall back to HTTP/1.1 if an HTTP/2 connection isn't established. For more information on HTTP/2 configuration with IIS deployments, see HTTP/2 on IIS.

Advanced HTTP/2 features to support gRPC

Additional HTTP/2 features in IIS support gRPC, including support for response trailers and sending reset frames.

Requirements to run gRPC on IIS:

  • In-process hosting.
  • Windows 11 Build 22000 or later, Windows Server 2022 Build 20348 or later.
  • TLS 1.2 or later connection.

Trailers

HTTP Trailers are similar to HTTP Headers, except they are sent after the response body is sent. For IIS and HTTP.sys, only HTTP/2 response trailers are supported.

if (httpContext.Response.SupportsTrailers())
{
    httpContext.Response.DeclareTrailer("trailername");	

    // Write body
    httpContext.Response.WriteAsync("Hello world");

    httpContext.Response.AppendTrailer("trailername", "TrailerValue");
}

In the preceding example code:

  • SupportsTrailers ensures that trailers are supported for the response.
  • DeclareTrailer adds the given trailer name to the Trailer response header. Declaring a response's trailers is optional, but recommended. If DeclareTrailer is called, it must be before the response headers are sent.
  • AppendTrailer appends the trailer.

Reset

Reset allows for the server to reset a HTTP/2 request with a specified error code. A reset request is considered aborted.

var resetFeature = httpContext.Features.Get<IHttpResetFeature>();
resetFeature.Reset(errorCode: 2);

Reset in the preceding code example specifies the INTERNAL_ERROR error code. For more information about HTTP/2 error codes, visit the HTTP/2 specification error code section.