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

Hello world - .NET Core

A simple web app written in C# using .NET 6.0 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.

Do the following steps to create the sample code and then deploy the app to your cluster. You can also download a working copy of the sample, by running the following commands:

git clone https://github.com/knative/docs.git knative-docs
cd knative-docs/code-samples/serving/hello-world/helloworld-csharp

Before you begin

• A Kubernetes cluster with Knative installed and DNS configured. See Install Knative Serving.
• Docker 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 6.0.

Recreating the sample code

1. First, make sure you have .NET SDK 6.0 installed:

   dotnet --version
   6.0.101
   

2. From the console, create a new empty web project using the dotnet command:

   dotnet new web -o helloworld-csharp
   

3. Update the Program.cs to read the port and define the serving url:

   var port = Environment.GetEnvironmentVariable("PORT") ?? "8080";
   var url = $"http://0.0.0.0:{port}";
   
   app.Run(url);
   

4. Update the Program.cs to read and return the TARGET environment variable:

   var target = Environment.GetEnvironmentVariable("TARGET") ?? "World";
   
   app.MapGet("/", () => $"Hello {target}!");
   

5. In your project directory, create a file named Dockerfile and copy the following code block into it. For detailed instructions on dockerizing an ASP.NET Core app, see Docker images for ASP.NET Core.

   # Use Microsoft's official build .NET image.
   FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build-env
   WORKDIR /app
   
   # Copy csproj and restore as distinct layers
   COPY *.csproj ./
   RUN dotnet restore
   
   # Copy everything else and build
   COPY . ./
   RUN dotnet publish -c Release -o out
   
   # Build runtime image
   FROM mcr.microsoft.com/dotnet/aspnet:6.0
   WORKDIR /app
   COPY --from=build-env /app/out .
   
   # Run the web service on container startup.
   ENTRYPOINT ["dotnet", "helloworld-csharp.dll"]
   

6. Create a .dockerignore file to ensure that any files related to a local build do not affect the container that you build for deployment.

   Dockerfile
   README.md
   **/obj/
   **/bin/
   

7. Create a new file, service.yaml and copy the following service definition into the file. Make sure to replace {username} with your Docker Hub username.

   apiVersion: serving.knative.dev/v1
   kind: Service
   metadata:
     name: helloworld-csharp
     namespace: default
   spec:
     template:
       spec:
         containers:
           - image: docker.io/{username}/helloworld-csharp
             env:
               - name: TARGET
                 value: "C# Sample v1"
   

Building and deploying the sample

Once you have recreated the sample code files (or used the files in the sample folder) you're ready to build and deploy the sample app.

1. Use Docker to build the sample code into a container. To build and push with Docker Hub, run these commands replacing {username} with your Docker Hub username:

   # Build and push the container on your local machine.
   docker buildx build --platform linux/arm64,linux/amd64 -t "{username}/helloworld-csharp" --push .
   

2. After the build has completed and the container is pushed to docker hub, you can deploy the app into your cluster. Ensure that the container image value in service.yaml matches the container you built in the previous step. Apply the configuration using kubectl:

   kubectl apply --filename service.yaml
   

3. Now that your service is created, Knative will perform the following steps:

   • Create a new immutable revision for this version of the app.
   • Network programming to create a route, ingress, service, and load balance for your app.
   • Automatically scale your pods up and down (including to zero active pods).

4. To find the URL for your service, use

   kubectl get ksvc helloworld-csharp  --output=custom-columns=NAME:.metadata.name,URL:.status.url
   NAME                URL
   helloworld-csharp   http://helloworld-csharp.default.1.2.3.4.sslip.io
   

5. Now you can make a request to your app and see the result. Replace the following URL with the URL returned in the previous command.

   curl http://helloworld-csharp.default.1.2.3.4.sslip.io
   Hello C# Sample v1!
   

Removing the sample app deployment

To remove the sample app from your cluster, delete the service record:

kubectl delete --filename service.yaml