An error occurred while starting the application.

一、.net core 发布后的站点启动报错如下

An error occurred while starting the application.

.NET Core 4.6.26328.01 X64 v4.0.0.0    |   Microsoft.AspNetCore.Hosting version 2.0.3-rtm-10026    |    Microsoft Windows 10.0.16299    |   Need help?

二、解决办法，先打开iis日志。web.config 修改如下（重点背景色黄色）

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <system.webServer>
    <directoryBrowse enabled="true" showFlags="Date, Time, Size, Extension, LongDate" />
    <handlers>
      <add name="aspNetCore" path="*" verb="*" modules="AspNetCoreModule" resourceType="Unspecified" />
    </handlers>
    <aspNetCore processPath="dotnet" arguments=".\GP.Core.WebAPI.dll" stdoutLogEnabled="true" stdoutLogFile=".\logs\stdout" />
  </system.webServer>
</configuration>

　　一般情况下我们发布后，都会存在这段代码，但是要把 stdoutLogEnabled="false" 换成 stdoutLogEnabled="true" 才能在根目录记录文本日志，查看异常原因。log日志文件夹需要手动创建！

三、刷新站点页面，查看发布根目录发现多了一个logs文件夹，打开里面的stdout_xxx.log文件，打开就可以看到我们站点启动失败的原因（eg：某些日志文件nlog.config或者文档xml等没有复制输出到发布目录）。

Application startup exception: System.IO.FileNotFoundException: Could not find file 'G:\FTP\DialysisWebApi\Dialysis.WebApi.xml'. File name: 'G:\FTP\DialysisWebApi\Dialysis.WebApi.xml'    at System.IO.Win32FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, FileStream parent)    at System.IO.Win32FileSystem.Open(String fullPath, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, FileStream parent)    at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options)    at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share)    at System.Xml.XmlSystemPathResolver.GetEntity(Uri uri, String role, Type typeOfObjectToReturn)    at System.Xml.XmlTextReaderImpl.FinishInitUriString()    at System.Xml.XmlTextReaderImpl..ctor(String uriStr, XmlReaderSettings settings, XmlParserContext context, XmlResolver uriResolver)    at System.Xml.XmlReaderSettings.CreateReader(String inputUri, XmlParserContext inputContext)    at System.Xml.XmlReader.Create(String inputUri)    at System.Xml.XPath.XPathDocument..ctor(String uri, XmlSpace space)    at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenOptions.<>c__DisplayClass24_0.<IncludeXmlComments>b__0()    at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenOptions.CreateSwaggerProvider(IServiceProvider serviceProvider)    at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitTransient(TransientCallSite transientCallSite, ServiceProvider provider)    at Microsoft.Extensions.DependencyInjection.ServiceProvider.<>c__DisplayClass16_0.<RealizeService>b__0(ServiceProvider provider)    at Microsoft.Extensions.Internal.ActivatorUtilities.ConstructorMatcher.CreateInstance(IServiceProvider provider)    at Microsoft.Extensions.Internal.ActivatorUtilities.CreateInstance(IServiceProvider provider, Type instanceType, Object[] parameters)    at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.<>c__DisplayClass3_0.<UseMiddleware>b__0(RequestDelegate next)    at Microsoft.AspNetCore.Builder.Internal.ApplicationBuilder.Build()    at Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication() Hosting environment: Production Content root path: G:\FTP\DialysisWebApi Now listening on: http://localhost:22365 Application started. Press Ctrl+C to shut down.

四、因为项目在startup的时候没有读到nlog.config这个文件导致的错误。解决办法：

　　在开发环境中，把这个文件的属性配置成 “生成操作：内容”和 “复制到输出目录：始终复制” 就可以了。