使用TestServer时，同服务器内HttpClient调用其他控制器失败

项目配置说明 #

我有一个ASP.NET Core Server项目，服务配置如下：

services.AddControllers()
    .AddApplicationPart(gatewayAssembly)
    .AddApplicationPart(identitiesMicroserviceAssembly)
    .AddApplicationPart(exceptionsMicroserviceAssembly)
    .etc ...;

网关程序集内的控制器通过HttpClient与微服务程序集内的控制器通信，HttpClient的基础Uri通过appsettings.json配置。开发环境的配置为：

"MicroserviceUris": {
    "Identities": "https://localhost:7138",
    "Exceptions": "https://localhost:7138",
    "Entitlements": "https://localhost:7138",
    "Organisations": "https://localhost:7138",
    "Catalogs": "https://localhost:7138",
    "Taxes":  "https://localhost:7138",
    "Warehouse": "https://localhost:7138"
  },

该配置可在微服务迁移时仅修改配置文件即可适配，通过Postman调用网关接口一切正常。

测试环境异常情况 #

使用TestServer进行集成测试时，integrationtestappsettings.json中配置的微服务基础Uri为http://localhost：

"MicroserviceUris": {
    "Identities": "http://localhost",
    "Exceptions": "http://localhost",
    "Entitlements": "http://localhost",
    "Organisations": "http://localhost",
    "Catalogs": "http://localhost",
    "Taxes": "http://localhost",
    "Warehouse": "http://localhost"
  },

测试项目直接调用网关路由正常，但网关控制器通过HttpClient调用微服务接口时返回404。直接从测试项目调用微服务路由http://localhost/api/identities/users是正常的，从日志可以看出二次请求返回404，问题应出在TestServer上创建的HttpClient。

相关日志信息 #

18:27:17.499info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
      => RequestPath:/api/uc/useraccountmanagement/registernewuser RequestId:0HMM1MRES2K3M
      Request starting HTTP/1.1 POST http://localhost/api/uc/useraccountmanagement/registernewuser application/json;+charset=utf-8 -
18:27:17.531info: Microsoft.AspNetCore.Routing.EndpointMiddleware[0]
      => RequestPath:/api/uc/useraccountmanagement/registernewuser RequestId:0HMM1MRES2K3M
      Executing endpoint 'Cosmos.Application.UseCases.UserAccountManagement.Controllers.RegisterNewUser.RegisterNewUserController.PostAsync (Cosmos.Application.UseCases.UserAccountManagement.Controllers)'
18:27:17.545info: Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker[3]
      => RequestPath:/api/uc/useraccountmanagement/registernewuser RequestId:0HMM1MRES2K3M => Cosmos.Application.UseCases.UserAccountManagement.Controllers.RegisterNewUser.RegisterNewUserController.PostAsync (Cosmos.Application.UseCases.UserAccountManagement.Controllers)
      Route matched with {action = "Post", controller = "RegisterNewUser"}. Executing controller action with signature System.Threading.Tasks.Task`1[Microsoft.AspNetCore.Mvc.IActionResult] PostAsync(Cosmos.Application.UseCases.UserAccountManagement.Models.RegisterNewUser.RegisterNewUserModel, System.Collections.Generic.IEnumerable`1[Microsoft.AspNetCore.Routing.EndpointDataSource]) on controller Cosmos.Application.UseCases.UserAccountManagement.Controllers.RegisterNewUser.RegisterNewUserController (Cosmos.Application.UseCases.UserAccountManagement.Controllers).
18:27:17.572info: System.Net.Http.HttpClient.IdentitiesProxy.LogicalHandler[100]
      => RequestPath:/api/uc/useraccountmanagement/registernewuser RequestId:0HMM1MRES2K3M => Cosmos.Application.UseCases.UserAccountManagement.Controllers.RegisterNewUser.RegisterNewUserController.PostAsync (Cosmos.Application.UseCases.UserAccountManagement.Controllers) => HTTP POST http://localhost/api/identities/users
      Start processing HTTP request POST http://localhost/api/identities/users
18:27:17.573info: System.Net.Http.HttpClient.IdentitiesProxy.ClientHandler[100]
      => RequestPath:/api/uc/useraccountmanagement/registernewuser RequestId:0HMM1MRES2K3M => Cosmos.Application.UseCases.UserAccountManagement.Controllers.RegisterNewUser.RegisterNewUserController.PostAsync (Cosmos.Application.UseCases.UserAccountManagement.Controllers) => HTTP POST http://localhost/api/identities/users
      Sending HTTP request POST http://localhost/api/identities/users
18:27:17.612info: System.Net.Http.HttpClient.IdentitiesProxy.ClientHandler[101]
      => RequestPath:/api/uc/useraccountmanagement/registernewuser RequestId:0HMM1MRES2K3M => Cosmos.Application.UseCases.UserAccountManagement.Controllers.RegisterNewUser.RegisterNewUserController.PostAsync (Cosmos.Application.UseCases.UserAccountManagement.Controllers) => HTTP POST http://localhost/api/identities/users
      Received HTTP response headers after 37.8005ms - 404
18:27:17.612info: System.Net.Http.HttpClient.IdentitiesProxy.LogicalHandler[101]
      => RequestPath:/api/uc/useraccountmanagement/registernewuser RequestId:0HMM1MRES2K3M => Cosmos.Application.UseCases.UserAccountManagement.Controllers.RegisterNewUser.RegisterNewUserController.PostAsync (Cosmos.Application.UseCases.UserAccountManagement.Controllers) => HTTP POST http://localhost/api/identities/users
      End processing HTTP request after 42.4879ms - 404

内容的提问来源于stack exchange，提问作者Neil W