CoreProgramm

 public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            app.UseCustomLoggerMiddleware();

            app.Run(async (context) =>
            {

CoreProgramm

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory logFactory)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            app.UseCustomLoggerMiddleware();

            app.Run(async (context) =>
            {

CoreProgramm

public class CustomLoggerMiddleware
    {
        private readonly RequestDelegate _next;
        private readonly ILogger _logger;
        public CustomLoggerMiddleware(RequestDelegate next, ILoggerFactory logFactory)
        {
            _next = next;
            _logger = logFactory.CreateLogger("MyMiddleware");
            _logger.LogInformation("MyMiddleware is Started");
        }

CoreProgramm

 // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            app.UseRouting();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapGet("/", async context =>
                {
                    throw new Exception("Error Occurred while processing your request");

CoreProgramm

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                DeveloperExceptionPageOptions developerExceptionPageOptions = 
                                                        new DeveloperExceptionPageOptions
                {
                    SourceCodeLineCount = 5
                };

CoreProgramm

 // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
           // app.UseFileServer();

            app.UseRouting();

CoreProgramm

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            app.UseFileServer();

            app.UseRouting();

CoreProgramm

    // You may need to install the Microsoft.AspNetCore.Http.Abstractions package into your project
    public class MyCustomMiddleware
    {
        private readonly RequestDelegate _next;

        public MyCustomMiddleware(RequestDelegate next)
        {
            _next = next;
        }

CoreProgramm

public static void Main(string[] args)
        {
            var host = new WebHostBuilder()
                       .UseKestrel()
                       .UseWebRoot("myCustomRoot")
                       .UseContentRoot(Directory.GetCurrentDirectory())
                       .UseIISIntegration()
                       .UseStartup<Startup>()
                       .Build();
               host.Run();

CoreProgramm

FileServerOptions fileServerOptions = new FileServerOptions();
fileServerOptions.DefaultFilesOptions.DefaultFileNames.Clear();
fileServerOptions.DefaultFilesOptions.DefaultFileNames.Add("custom.html");
app.UseFileServer(fileServerOptions);