Lab: Build ASP.NET Web App

Introduction

In this lab, you will create a GitHub Actions workflow that builds and publishes an ASP.NET Core Web App. The workflow triggers on code changes in the src/dotnet/WebApp/ directory and can also be run manually. You will also learn how to change the runner environment to macOS, Windows, or a self-hosted runner.

Estimated Duration: 20–30 minutes

Instructions

Step 1: Set up your repository

  1. Navigate to the GitHub repository where your ASP.NET Web App source code is located.

    • The web app should reside in the path: src/dotnet/WebApp.
    • If you don’t have this structure yet, create the folders and add a sample .csproj file and Program.cs to simulate the project.

Step 2: Create the workflow file

  1. In the repository, go to the Code tab.

  2. Click Add file > Create new file.

  3. Name the file: .github/workflows/aspnet-webapp-build.yml

  4. Paste the following workflow YAML:

    name: ASP.NET Web App Build

on:
  push:
    paths:
      - 'src/dotnet/WebApp/**'
  workflow_dispatch:

jobs:
  build:
    runs-on: ubuntu-latest
    defaults:
      run:
        working-directory: ./src/dotnet/WebApp
    steps:
      - name: Checkout Code
        uses: actions/checkout@v4.1.7

      - name: Set up .NET Core
        uses: actions/setup-dotnet@v4.0.1
        with:
          dotnet-version: '8.x'

      - name: Build Code
        run: dotnet build --configuration Release

      - name: Publish Code
        run: dotnet publish -c Release --property:PublishDir="$/webapp"

  5. Click Commit new file to save the workflow.

Step 3: Understand the workflow

Step 4: Test the workflow

  1. Make a small change to any file under src/dotnet/WebApp/ and push it to GitHub.
  2. Alternatively, go to the Actions tab and run the workflow manually using Run workflow.
  3. View the workflow logs in the Actions tab.
  4. Confirm successful execution of all steps.

Step 5: Change the runner environment

You can change the runner by updating the runs-on property in the workflow.

a. Use a Windows runner

runs-on: windows-latest

b. Use a macOS runner

runs-on: macos-latest

c. Use a self-hosted runner

To use a self-hosted runner, make sure you’ve registered a runner in your repo/org. Then change:

runs-on: self-hosted

You can also target a specific label if you’ve added one during runner setup:

runs-on: [self-hosted, windows, x64]

✅ Tip: Self-hosted runners require manual setup. Refer to GitHub Docs - Self-hosted runners for guidance.

Step 6: Try with different runners (Optional)

  1. Modify the workflow to use one of the alternative runners.
  2. Commit the changes.

  3. Re-run the workflow to observe platform-specific behavior.

    • On macOS or Windows, the behavior of SDK setup and file paths may differ slightly.

Summary

In this lab, you created a workflow to build and publish an ASP.NET Core Web App using GitHub Actions. You learned how to:

Additional Resources

  1. GitHub Actions for .NET
  2. Self-hosted Runners
  3. .NET CLI - dotnet build