.NET Core如何将不同子域名请求转发到不同本地端口？

不管是自定义中间件还是YARP都能实现这个需求，YARP其实支持基于主机头的路由规则，可能是你没找对配置方式。下面给两种可行的实现方案：

一、自定义中间件实现 #

如果想自己控制转发逻辑，可以写个简单的中间件：

1. 先创建中间件类，解析请求的子域名，匹配对应的目标端口：

public class SubdomainProxyMiddleware
{
    private readonly RequestDelegate _next;
    private readonly HttpClient _httpClient;

    public SubdomainProxyMiddleware(RequestDelegate next, HttpClient httpClient)
    {
        _next = next;
        _httpClient = httpClient;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        var host = context.Request.Host.Host;
        string targetBaseUrl = host switch
        {
            "app1.localhost" => "http://localhost:5001",
            "app2.localhost" => "http://localhost:5002",
            // 可添加更多子域名映射
            _ => null
        };

        if (targetBaseUrl != null)
        {
            // 拼接目标URL，保留原请求的路径和查询参数
            var targetUrl = new Uri(new Uri(targetBaseUrl), context.Request.Path + context.Request.QueryString);
            
            // 构建转发请求
            var requestMessage = new HttpRequestMessage(new HttpMethod(context.Request.Method), targetUrl);
            
            // 复制原请求的所有头信息
            foreach (var header in context.Request.Headers)
            {
                if (!requestMessage.Headers.TryAddWithoutValidation(header.Key, header.Value.ToArray()) && requestMessage.Content != null)
                {
                    requestMessage.Content.Headers.TryAddWithoutValidation(header.Key, header.Value.ToArray());
                }
            }
            
            // 发送请求并获取响应
            var responseMessage = await _httpClient.SendAsync(requestMessage, HttpCompletionOption.ResponseHeadersRead, context.RequestAborted);
            
            // 将响应状态码和头信息回写给客户端
            context.Response.StatusCode = (int)responseMessage.StatusCode;
            foreach (var header in responseMessage.Headers)
            {
                context.Response.Headers.TryAdd(header.Key, header.Value.ToArray());
            }
            foreach (var header in responseMessage.Content.Headers)
            {
                context.Response.Headers.TryAdd(header.Key, header.Value.ToArray());
            }
            
            // 复制响应内容到客户端
            await responseMessage.Content.CopyToAsync(context.Response.Body);
            return;
        }

        // 未匹配到子域名，继续执行后续中间件逻辑
        await _next(context);
    }
}

2. 在Program.cs中注册中间件和HttpClient：

var builder = WebApplication.CreateBuilder(args);

// 注册HttpClient供中间件使用
builder.Services.AddHttpClient<SubdomainProxyMiddleware>();

var app = builder.Build();

// 启用自定义代理中间件
app.UseMiddleware<SubdomainProxyMiddleware>();

app.Run();

二、用YARP实现（更推荐生产环境） #

YARP完全支持基于主机头的路由，只需简单配置即可：

1. 先安装YARP包：

dotnet add package Yarp.ReverseProxy

2. 在appsettings.json中配置路由和集群，指定不同子域名对应不同本地端口：

{
  "ReverseProxy": {
    "Routes": {
      "app1_route": {
        "ClusterId": "app1_cluster",
        "Match": {
          "Hosts": [ "app1.localhost" ]
        }
      },
      "app2_route": {
        "ClusterId": "app2_cluster",
        "Match": {
          "Hosts": [ "app2.localhost" ]
        }
      }
    },
    "Clusters": {
      "app1_cluster": {
        "Destinations": {
          "app1": {
            "Address": "http://localhost:5001/"
          }
        }
      },
      "app2_cluster": {
        "Destinations": {
          "app2": {
            "Address": "http://localhost:5002/"
          }
        }
      }
    }
  }
}

3. 在Program.cs中启用YARP：

var builder = WebApplication.CreateBuilder(args);

// 添加YARP服务并加载配置
builder.Services.AddReverseProxy()
    .LoadFromConfig(builder.Configuration.GetSection("ReverseProxy"));

var app = builder.Build();

// 映射反向代理路由
app.MapReverseProxy();

app.Run();

本地测试必做配置 #

不管用哪种方案，本地测试时都需要修改hosts文件（Windows路径：C:\Windows\System32\drivers\etc\hosts；Linux/macOS路径：/etc/hosts），添加如下映射：

127.0.0.1 app1.localhost app2.localhost

这样本地才能正常解析这些子域名。

内容的提问来源于stack exchange，提问作者gartenkralle