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Use HTTP/2 with the ASP.NET Core Kestrel web server

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Note

This isn't the latest version of this article. For the current release, see the .NET 9 version of this article.

Warning

This version of ASP.NET Core is no longer supported. For more information, see .NET and .NET Core Support Policy. For the current release, see the .NET 8 version of this article.

Important

This information relates to a pre-release product that may be substantially modified before it's commercially released. Microsoft makes no warranties, express or implied, with respect to the information provided here.

For the current release, see the .NET 9 version of this article.

HTTP/2 is available for ASP.NET Core apps if the following base requirements are met:

  • Operating system
    • Windows Server 2016/Windows 10 or later‡
    • Linux with OpenSSL 1.0.2 or later (for example, Ubuntu 16.04 or later)
    • macOS 10.15 or later
  • Target framework: .NET Core 2.2 or later
  • Application-Layer Protocol Negotiation (ALPN) connection
  • TLS 1.2 or later connection

‡Kestrel has limited support for HTTP/2 on Windows Server 2012 R2 and Windows 8.1. Support is limited because the list of supported TLS cipher suites available on these operating systems is limited. A certificate generated using an Elliptic Curve Digital Signature Algorithm (ECDSA) may be required to secure TLS connections.

If an HTTP/2 connection is established, HttpRequest.Protocol reports HTTP/2.

Starting with .NET Core 3.0, HTTP/2 is enabled by default. For more information on configuration, see the Kestrel HTTP/2 limits and ListenOptions.Protocols sections.

Advanced HTTP/2 features

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

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.

HTTP/2 is available for ASP.NET Core apps if the following base requirements are met:

  • Operating system†
    • Windows Server 2016/Windows 10 or later‡
    • Linux with OpenSSL 1.0.2 or later (for example, Ubuntu 16.04 or later)
  • Target framework: .NET Core 2.2 or later
  • Application-Layer Protocol Negotiation (ALPN) connection
  • TLS 1.2 or later connection

†HTTP/2 will be supported on macOS in a future release. ‡Kestrel has limited support for HTTP/2 on Windows Server 2012 R2 and Windows 8.1. Support is limited because the list of supported TLS cipher suites available on these operating systems is limited. A certificate generated using an Elliptic Curve Digital Signature Algorithm (ECDSA) may be required to secure TLS connections.

If an HTTP/2 connection is established, HttpRequest.Protocol reports HTTP/2.

Starting with .NET Core 3.0, HTTP/2 is enabled by default. For more information on configuration, see the Kestrel HTTP/2 limits and ListenOptions.Protocols sections.

Advanced HTTP/2 features

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

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.

HTTP/2 is available for ASP.NET Core apps if the following base requirements are met:

  • Operating system†
    • Windows Server 2016/Windows 10 or later‡
    • Linux with OpenSSL 1.0.2 or later (for example, Ubuntu 16.04 or later)
  • Target framework: .NET Core 2.2 or later
  • Application-Layer Protocol Negotiation (ALPN) connection
  • TLS 1.2 or later connection

†HTTP/2 will be supported on macOS in a future release. ‡Kestrel has limited support for HTTP/2 on Windows Server 2012 R2 and Windows 8.1. Support is limited because the list of supported TLS cipher suites available on these operating systems is limited. A certificate generated using an Elliptic Curve Digital Signature Algorithm (ECDSA) may be required to secure TLS connections.

If an HTTP/2 connection is established, HttpRequest.Protocol reports HTTP/2.

Starting with .NET Core 3.0, HTTP/2 is enabled by default. For more information on configuration, see the Kestrel HTTP/2 limits and ListenOptions.Protocols sections.

Advanced HTTP/2 features

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

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.