.NET 6调用UseWindowsService()抛出NotSupportedException异常

问题复现 #

Program.cs 原始代码 #

var builder = WebApplication.CreateBuilder(args);

builder.Host.UseWindowsService();

// Add services to the container.
builder.Services.AddGrpc();

var app = builder.Build();

// Configure the HTTP request pipeline.
app.MapGrpcService<GreeterService>();
app.MapGet("/", () => "error");

app.Run();

引用NuGet包 #

• Grpc.AspNetCore(2.47.0)
• Microsoft.Extensions.Hosting.WindowsServices (6.0.0)

错误日志 #

Application: PartReservationGrpc.exe CoreCLR Version: 6.0.622.26707
.NET Version: 6.0.6 Description: The process was terminated due to an unhandled exception. Exception Info: System.NotSupportedException: The content root changed from "C:\windows\system32" to "D:\CMAP\iceman\partreservation". Changing the host configuration using WebApplicationBuilder.Host is not supported. Use WebApplication.CreateBuilder(WebApplicationOptions) instead. at Microsoft.AspNetCore.Builder.ConfigureHostBuilder.ConfigureHostConfiguration(Action1 configureDelegate) at Microsoft.Extensions.Hosting.HostingHostBuilderExtensions.UseContentRoot(IHostBuilder hostBuilder, String contentRoot) at Microsoft.Extensions.Hosting.WindowsServiceLifetimeHostBuilderExtensions.UseWindowsService(IHostBuilder hostBuilder, Action1 configure) at Microsoft.Extensions.Hosting.WindowsServiceLifetimeHostBuilderExtensions.UseWindowsService(IHostBuilder hostBuilder) at Program.$(String[] args) in C:\Users\WuJ22\source\Workspaces\C5CG2133PXF\gRPC\PartReservation\PartReservation\PartReservationGrpc\Program.cs:line 33

报错原因 #

这是.NET 6+最小托管模型的明确行为限制：WebApplicationBuilder初始化完成后，不允许通过builder.Host属性修改主机配置。而UseWindowsService()内部逻辑会自动修改主机内容根路径——Windows服务默认工作目录是C:\Windows\system32，方法会把路径改成服务EXE所在的实际部署目录，这个修改动作直接触发了NotSupportedException。

修复方法 #

直接调整Program.cs代码，按照错误提示使用WebApplicationOptions在初始化Builder时提前指定内容根路径，同时将Windows服务注册逻辑从builder.Host迁移到服务集合注册即可：

// 初始化Builder时提前传入配置，指定内容根路径和启动参数
var builder = WebApplication.CreateBuilder(new WebApplicationOptions
{
    Args = args,
    ContentRootPath = AppContext.BaseDirectory
});

// 替换原来的builder.Host.UseWindowsService()，使用服务集合的扩展方法注册Windows服务
builder.Services.AddWindowsService();

// 其余服务注册、中间件配置代码保持不变
builder.Services.AddGrpc();

var app = builder.Build();

app.MapGrpcService<GreeterService>();
app.MapGet("/", () => "error");

app.Run();

修改完成后重新编译发布，再注册启动Windows服务即可正常运行。
注意：6.0.0及以上版本的Microsoft.Extensions.Hosting.WindowsServices包已经自带AddWindowsService()扩展方法，不需要额外升级依赖。

内容的提问来源于stack exchange，提问作者Johnny Wu