ASP.NET Core跨平台技术内幕

ASP.NET Core设计初衷是开源跨平台、高性能Web服务器，其中跨平台特性较早期ASP.NET是一个显著的飞跃，.NET现可以理直气壮与JAVA同台竞技，而ASP.NET Core的高性能特性更是成为致胜法宝。

ASP.NET Core 2.1+为IIS托管新增In-Process模型并作为默认选项（使用IISHttpServer替代了Kestrel，dotnet程序由IIS网站进程w3wp.exe内部托管）。

为展示ASP.NET Core跨平台特性，本文重点着墨经典的Out-Process托管模型。

宏观设计

为解耦平台web服务器差异，程序内置Http服务组件Kestrel，由web服务器转发请求到Kestrel。

老牌web服务器定位成反向代理服务器，转发请求到ASP.NET Core程序（分别由IIS ASP.NET Core Module和Nginx负责）

常规代理服务器，只用于代理内部主机对外网的连接需求，一般不支持外部对内部网络的访问请求；当一个代理服务器能够代理外部网络的主机，访问内部网络，这种代理服务器被称为反向代理服务器。

平台web代理服务器、ASP.NET Core程序(dotnet.exe) 均为独立进程，平台自行决定互动细节，只需确保平台web服务器与Kestrel形成Http通信。

Kestrel

与老牌web服务器解耦，实现跨平台部署。

Kestrel使ASP.NET Core具备了基本web服务器的能力，在内网部署和开发环境完全可使用dotnet.exe自宿模式运行。
Kestrel定位是Http服务组件，实力还比不上老牌web服务器，在timeout机制、web缓存、响应压缩等不占优势，在安全性等方面还有缺陷。

因此在生产环境中必须使用老牌web服务器反向代理请求。

跨平台管控程序，转发请求

要实现企业级稳定部署：

ASP.NET Core跨平台技术内幕 *nix平台

将ASP.NET Core程序以dotnet.exe自宿模式运行，并配置为系统守护进程（管控应用），再由Nginx转发请求。

以下使用systemd创建进程服务文件

/etc/systemd/system/kestrel-eqidproxyserver.service

[Unit]Description=EqidProxyServer deploy on centos
[Service]WorkingDirectory=/var/www/eqidproxyserver/eqidproxyServerExecStart=/usr/bin/dotnet /var/www/eqidproxyserver/eqidproxyServer/EqidProxyServer.dllRestart=always# Restart service after 10 seconds if the dotnet service crashes:RestartSec=10TimeoutStopSec=90KillSignal=SIGINTSyslogIdentifier=dotnet-exampleUser=rootEnvironment=ASPNETCORE_ENVIRONMENT=ProductionEnvironment=DOTNET_PRINT_TELEMETRY_MESSAGE=false
[Install]WantedBy=multi-user.target
// 启用服务，在localhost:5000端口侦听请求sudo systemctl enable kestrel-eqidproxyserver.service

安装Nginx，并配置Nginx转发请求到localhost:5000:

server { 
    listen 80; 
    server_name default_website; 
    root /usr/share/nginx/html;
    # Load configuration files for the default server block. include /etc/nginx/default.d/*.conf;
    location / { 
        proxy_pass http://localhost:5000; 
        proxy_http_version 1.1; 
        proxy_set_header Upgrade $http_upgrade; proxy_set_header Connection keep-alive;
        proxy_set_header Host $host; 
        proxy_cache_bypass $http_upgrade; 
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; 
        proxy_set_header X-Forwarded-Proto $scheme; 
    } 
}

Windows平台

[ 管控应用、转发请求] 由ASP.NET Core Module(插入在IIS Pipeline中的原生组件，下面简称ACM)一手操办，w3wp.exe、dotnet.exe的互动关系是通过父子进程维系。

下图脚本力证dotnet.exe进程是w3wp.exe创建出来的子进程：

ASP.NET Core跨平台技术内幕得益此关系，ACM在创建dotnet.exe子进程时能指定环境变量，约定donet.exe接收（IIS转发的请求）的侦听端口。

实际源码看ACM为子进程设定三个重要的环境变量：

ASPNETCORE_PORT 约定 Kestrel将会在此端口上监听
ASPNETCORE_APPL_PATH
ASPNETCORE_TOKEN 约定携带该Token的请求为合法的转发请求

与ACM夫唱妇随的是UseIISIntegration扩展方法，完成如下工作：

① 启动Kestrel服务在http://localhost:{ASPNETCORE_PORT}上监听

② 根据 {ASPNETCORE_TOKEN} 检查请求是否来自ACM转发

ACM转发的请求，会携带名为MS-ASPNETCORE-TOKEN:******的Request Header,以便dotnet.exe对比研判。

③ 利用ForwardedHeaderMiddleware中间件保存原始请求信息

linux平台部署需要手动启用ForwardedHeader middleware https://docs.microsoft.com

/en-us/aspnet/core/host-and-deploy/proxy-load-balancer?view=aspnetcore-3.1

源码快速验证：

namespace Microsoft.AspNetCore.Hosting{
    public static class WebHostBuilderIISExtensions {
        // These are defined as ASPNETCORE_ environment variables by IIS's AspNetCoreModule. 
        private static readonly string ServerPort = "PORT";
        private static readonly string ServerPath = "APPL_PATH";
        private static readonly string PairingToken = "TOKEN";
        private static readonly string IISAuth = "IIS_HTTPAUTH";
        private static readonly string IISWebSockets = "IIS_WEBSOCKETS_SUPPORTED";
        /// <summary> /// Configures the port and base path the server should listen on when running behind AspNetCoreModule.  
        /// The app will also be configured to capture startup errors. 
        public static IWebHostBuilder UseIISIntegration(this IWebHostBuilder hostBuilder) 
        {
            var port = hostBuilder.GetSetting(ServerPort) ?? Environment.GetEnvironmentVariable($"ASPNETCORE_{ServerPort}");
            var path = hostBuilder.GetSetting(ServerPath) ?? Environment.GetEnvironmentVariable($"ASPNETCORE_{ServerPath}");
            var pairingToken = hostBuilder.GetSetting(PairingToken) ?? Environment.GetEnvironmentVariable($"ASPNETCORE_{PairingToken}");
            var iisAuth = hostBuilder.GetSetting(IISAuth) ?? Environment.GetEnvironmentVariable($"ASPNETCORE_{IISAuth}");
            var websocketsSupported = hostBuilder.GetSetting(IISWebSockets) ?? Environment.GetEnvironmentVariable($"ASPNETCORE_{IISWebSockets}");
            bool isWebSocketsSupported;
            if (!bool.TryParse(websocketsSupported, out isWebSocketsSupported)) 
            {
                // If the websocket support variable is not set, we will always fallback to assuming websockets are enabled.
                isWebSocketsSupported = (Environment.OSVersion.Version >= new Version(6, 2)); 
            }
            if (!string.IsOrEmpty(port) && !string.IsOrEmpty(path) && !string.IsOrEmpty(pairingToken)) 
            {
                // Set flag to prevent double service configuration
                hostBuilder.UseSetting(nameof(UseIISIntegration), true.ToString);
                var enableAuth = false; 
                if (string.IsOrEmpty(iisAuth)) 
                {
                    // back compat with older ANCM versions
                    enableAuth = true; 
                } else { /
                    / Lightup a new ANCM variable that tells us if auth is enabled.
                    foreach (var authType in iisAuth.Split(new[] { ';' }, StringSplitOptions.RemoveEmptyEntries)) 
                    {
                        if (!string.Equals(authType, "anonymous", StringComparison.OrdinalIgnoreCase)) 
                        { 
                            enableAuth = true; break; 
                        } 
                    } 
                }
                var address = "http://127.0.0.1:" + port; hostBuilder.CaptureStartupErrors(true);
                hostBuilder.ConfigureServices(services => {
                    // Delay register the url so users don't accidentally overwrite it.
                    hostBuilder.UseSetting(WebHostDefaults.ServerUrlsKey, address);
                    hostBuilder.PreferHostingUrls(true);
                    services.AddSingleton<IServerIntegratedAuth>(_ => new ServerIntegratedAuth { IsEnabled = enableAuth, AuthenticationScheme = IISDefaults.AuthenticationScheme 
                });
                services.AddSingleton<IStartupFilter>(new IISSetupFilter(pairingToken, new PathString(path), isWebSocketsSupported)); services.Configure<ForwardedHeadersOptions>(options => { options.ForwardedHeaders = ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto; });
                services.Configure<IISOptions>(options => { options.ForwardWindowsAuthentication = enableAuth; }); services.AddAuthenticationCore; });
            }
            return hostBuilder;
        }
    }
}

总结

ASP.NET Core跨平台的核心在于程序内置Kestrel HTTP通信组件，解耦web服务器差异；依平台特性约定Http通信细节。

本文从框架设计初衷、进程模型、组件交互验证我对ASP.NET Core跨平台特性的理解。

+ CentOS上部署ASP.NET Core完整版请参考：https://www.cnblogs.com/JulianHuang/p/10455644.html

让干货飞一会。

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