Changed C# sample to use .NET Core 3.0 and more lean and secure alpine as base image (#1816)

* Changed C# sample to use more lean and secure alpine as base image

* Updated sample to use .NET Core 3.0

* Fixed typos in README.md

* Fixed indentation

docs/serving/samples/hello-world/helloworld-csharp/Dockerfile

@@ -1,6 +1,6 @@
 # Use Microsoft's official build .NET image.
 # https://hub.docker.com/_/microsoft-dotnet-core-sdk/
-FROM mcr.microsoft.com/dotnet/core/sdk:2.2 AS build
+FROM mcr.microsoft.com/dotnet/core/sdk:3.0-alpine AS build
 WORKDIR /app
 
 # Install production dependencies.
@@ -18,7 +18,7 @@ RUN dotnet publish -c Release -o out
 
 # Use Microsoft's official runtime .NET image.
 # https://hub.docker.com/_/microsoft-dotnet-core-aspnet/
-FROM mcr.microsoft.com/dotnet/core/aspnet:2.2 AS runtime
+FROM mcr.microsoft.com/dotnet/core/aspnet:3.0-alpine AS runtime
 WORKDIR /app
 COPY --from=build /app/out ./
 

docs/serving/samples/hello-world/helloworld-csharp/Program.cs

@@ -1,6 +1,6 @@
 using System;
-using Microsoft.AspNetCore;
 using Microsoft.AspNetCore.Hosting;
+using Microsoft.Extensions.Hosting;
 
 namespace helloworld_csharp
 {
@@ -8,16 +8,19 @@ namespace helloworld_csharp
     {
         public static void Main(string[] args)
         {
-            CreateWebHostBuilder(args).Build().Run();
+            CreateHostBuilder(args).Build().Run();
         }
 
-        public static IWebHostBuilder CreateWebHostBuilder(string[] args)
+        public static IHostBuilder CreateHostBuilder(string[] args)
         {
             string port = Environment.GetEnvironmentVariable("PORT") ?? "8080";
             string url = String.Concat("http://0.0.0.0:", port);
 
-            return WebHost.CreateDefaultBuilder(args)
+            return Host.CreateDefaultBuilder(args)
-                .UseStartup<Startup>().UseUrls(url);
+                .ConfigureWebHostDefaults(webBuilder =>
+                {
+                    webBuilder.UseStartup<Startup>().UseUrls(url);
+                });
         }
     }
 }

docs/serving/samples/hello-world/helloworld-csharp/README.md

@@ -5,7 +5,7 @@ weight: 1
 type: "docs"
 ---
 
-A simple web app written in C# using .NET Core 2.2 that you can use for testing.
+A simple web app written in C# using .NET Core 3.0 that you can use for testing.
 It reads in an env variable `TARGET` and prints "Hello \${TARGET}!". If TARGET
 is not specified, it will use "World" as the TARGET.
 
@@ -25,16 +25,16 @@ cd knative-docs/docs/serving/samples/hello-world/helloworld-csharp
   create one.
 - [Docker](https://www.docker.com) installed and running on your local machine,
   and a Docker Hub account configured (we'll use it for a container registry).
-- You have installed [.NET Core SDK 2.2](https://www.microsoft.com/net/core).
+- You have installed [.NET Core SDK 3.0](https://www.microsoft.com/net/core).
 
 ## Recreating the sample code
 
 1. First, make sure you have
-   [.NET Core SDK 2.2](https://www.microsoft.com/net/core) installed:
+   [.NET Core SDK 3.0](https://www.microsoft.com/net/core) installed:
 
    ```shell
    dotnet --version
-   2.2.102
+   3.0.100
    ```
 
 1. From the console, create a new empty web project using the dotnet command:
@@ -43,29 +43,35 @@ cd knative-docs/docs/serving/samples/hello-world/helloworld-csharp
    dotnet new web -o helloworld-csharp
    ```
 
-1. Update the `CreateWebHostBuilder` definition in `Program.cs` by adding
+1. Update the `CreateHostBuilder` definition in `Program.cs` by adding
    `.UseUrls()` to define the serving port:
 
    ```csharp
-   public static IWebHostBuilder CreateWebHostBuilder(string[] args)
+   public static IHostBuilder CreateHostBuilder(string[] args)
    {
        string port = Environment.GetEnvironmentVariable("PORT") ?? "8080";
        string url = String.Concat("http://0.0.0.0:", port);
 
-       return WebHost.CreateDefaultBuilder(args)
+      return Host.CreateDefaultBuilder(args)
-           .UseStartup<Startup>().UseUrls(url);
+          .ConfigureWebHostDefaults(webBuilder =>
+          {
+              webBuilder.UseStartup<Startup>().UseUrls(url);
+          });
    }
    ```
 
-1. Update the `app.Run(...)` statement in `Startup.cs` to read and return the
+1. Update the `app.UseEndpoints(...)` statement in `Startup.cs` to read and return the
    TARGET environment variable:
 
    ```csharp
-   app.Run(async (context) =>
+   app.UseEndpoints(endpoints =>
+   {
+      endpoints.MapGet("/", async context =>
       {
           var target = Environment.GetEnvironmentVariable("TARGET") ?? "World";
           await context.Response.WriteAsync($"Hello {target}!\n");
       });
+   });
    ```
 
 1. In your project directory, create a file named `Dockerfile` and copy the code
@@ -76,7 +82,7 @@ cd knative-docs/docs/serving/samples/hello-world/helloworld-csharp
    ```docker
    # Use Microsoft's official build .NET image.
    # https://hub.docker.com/_/microsoft-dotnet-core-sdk/
-   FROM mcr.microsoft.com/dotnet/core/sdk:2.2 AS build
+   FROM mcr.microsoft.com/dotnet/core/sdk:3.0-alpine AS build
    WORKDIR /app
  
    # Install production dependencies.
@@ -91,10 +97,9 @@ cd knative-docs/docs/serving/samples/hello-world/helloworld-csharp
    # Build a release artifact.
    RUN dotnet publish -c Release -o out
 
-   
    # Use Microsoft's official runtime .NET image.
    # https://hub.docker.com/_/microsoft-dotnet-core-aspnet/
-   FROM mcr.microsoft.com/dotnet/core/aspnet:2.2 AS runtime
+   FROM mcr.microsoft.com/dotnet/core/aspnet:3.0-alpine AS runtime
    WORKDIR /app
    COPY --from=build /app/out ./
 

docs/serving/samples/hello-world/helloworld-csharp/Startup.cs

@@ -3,6 +3,7 @@ using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
 
 namespace helloworld_csharp
 {
@@ -15,18 +16,23 @@ namespace helloworld_csharp
         }
 
         // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
-        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
+        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
         {
             if (env.IsDevelopment())
             {
                 app.UseDeveloperExceptionPage();
             }
 
-            app.Run(async (context) =>
+            app.UseRouting();
+
+            app.UseEndpoints(endpoints =>
+            {
+                endpoints.MapGet("/", async context =>
                 {
                     var target = Environment.GetEnvironmentVariable("TARGET") ?? "World";
                     await context.Response.WriteAsync($"Hello {target}!\n");
                 });
+            });
         }
     }
 }

docs/serving/samples/hello-world/helloworld-csharp/helloworld-csharp.csproj

@@ -1,15 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk.Web">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
+    <RootNamespace>helloworld_csharp</RootNamespace>
   </PropertyGroup>
 
-  <ItemGroup>
-    <Folder Include="wwwroot\" />
-  </ItemGroup>
-
-  <ItemGroup>
-    <PackageReference Include="Microsoft.AspNetCore.App" />
-  </ItemGroup>
-
 </Project>