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。
因此在生产环境中建议使用老牌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：
*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/eqidproxyServer
ExecStart=/usr/bin/dotnet /var/www/eqidproxyserver/eqidproxyServer/EqidProxyServer.dll
Restart=always
# Restart service after 10 seconds if the dotnet service crashes:
RestartSec=10
TimeoutStopSec=90
KillSignal=SIGINT
SyslogIdentifier=dotnet-example
User=root
Environment=ASPNETCORE_ENVIRONMENT=Production
Environment=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 $scheme;
}
}Windows平台
[ 管控应用、转发请求] 由ASP.NET Core Module(插入在IIS Pipeline中的原生组件，下面简称ACM)一手操办，w3wp.exe、dotnet.exe的互动关系是通过父子进程维系。
下图脚本力证dotnet.exe进程是w3wp.exe创建出来的子进程：
得益此关系，ACM在创建dotnet.exe子进程时能指定环境变量，约定donet.exe接收（IIS转发的请求）的侦听端口。
实际源码看ACM为子进程设定三个重要的环境变量：
- ASPNETCORE_PORT 约定 Kestrel将会在此端口上监听
- ASPNETCORE_APPL_PATH
- ASPNETCORE_TOKEN 约定 携带该Token的请求为合法的转发请求
与ACM夫唱妇随的是UseIISIntegration()扩展方法，完成如下工作：
① 启动Kestrel服务在http://localhost:{ASPNETCORE_PORT}上监听
② 根据 {ASPNETCORE_TOKEN} 检查请求是否来自ACM转发
ACM转发的请求，会携带名为MS-ASPNETCORE-TOKEN:******的Request Header,以便dotnet.exe对比研判。
③ 利用ForwardedHeaderMiddleware中间件保存原始请求信息
linux平台部署需要手动启用ForwardedHeader middleware https://docs.microsoft.com/en-us/aspnet/core/host-and-deploy/proxy-load-balancer?view=aspnetcore-3.1
源码快速验证：
namespace Microsoft.AspNetCore.Hosting
{
public static class WebHostBuilderIISExtensions
{
// These are defined as ASPNETCORE_ environment variables by IIS's AspNetCoreModule.
private static readonly string ServerPort = "PORT";
private static readonly string ServerPath = "APPL_PATH";
private static readonly string PairingToken = "TOKEN";
private static readonly string IISAuth = "IIS_HTTPAUTH";
private static readonly string IISWebSockets = "IIS_WEBSOCKETS_SUPPORTED";
/// <summary>
/// Configures the port and base path the server should listen on when running behind AspNetCoreModule.
/// The app will also be configured to capture startup errors.
public static IWebHostBuilder UseIISIntegration(this IWebHostBuilder hostBuilder)
{
var port = hostBuilder.GetSetting(ServerPort) ?? Environment.GetEnvironmentVariable($"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.IsNullOrEmpty(port) && !string.IsNullOrEmpty(path) && !string.IsNullOrEmpty(pairingToken))
{
// Set flag to prevent double service configuration
hostBuilder.UseSetting(nameof(UseIISIntegration), true.ToString());
var enableAuth = false;
if (string.IsNullOrEmpty(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。
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