Lab: Publish ASP.NET Web API as a Docker Image

Introduction

In this lab, you will learn how to publish an ASP.NET Core Web API as a Docker image using GitHub Actions. You will:

If you haven’t created the ASP.NET Web API Project, refer to the Create an ASP.NET Core Web API Project lab instructions before proceeding.

Duration: 30–40 minutes

Prerequisites

  1. Docker Hub Account:

    • Create an account at Docker Hub if you don’t already have one.

  2. GitHub Repository Secrets:

    • Add two secrets to your GitHub repository:
      • DOCKER_USERNAME: Your Docker Hub username.
      • DOCKER_PASSWORD: Your Docker Hub PAT.

  3. Ensure the ASP.NET Web API Project exists in the ./src/dotnet/Weather.WebApi directory.

Instructions

Step 1: Create a Docker Workflow

  1. Navigate to your GitHub repository directory and open the .github/workflows folder.
  2. Create a new file named aspnet-webapi-publish-docker-image.yml.

  3. Copy the following workflow content into the file:

    name: ASP.NET Web API Publish Docker Image
on:
  workflow_dispatch:
  push:
    paths:
      - '.github/workflows/aspnet-webapi-publish-docker-image.yml'
      - 'src/dotnet/Weather.WebApi/**'

env:
  DOCKER_IMAGE: prasadhonrao/aspnet-weather-webapi

jobs:
  build:
    runs-on: ubuntu-latest
    defaults:
      run:
        working-directory: ./src/dotnet/Weather.WebApi
    permissions:
      contents: read
    steps:
      - name: Checkout Code
        uses: actions/checkout@v4

      - name: Build ASP.NET Weather Web API
        run: dotnet build

      - name: Build Local Docker Image
        run: docker image build -t aspnet-weather-webapi .

      - name: List Docker Images
        run: docker image ls

      - name: Log in to Docker Hub
        uses: docker/login-action@v2
        with:
          username: $
          password: $

      - name: Tag Image to latest
        run: docker tag aspnet-weather-webapi $:latest

      - name: Push Image with latest tag to Docker Hub Registry
        run: docker push $:latest

      - name: List Docker Images
        run: docker image ls
  4. Replace prasadhonrao/aspnet-weather-webapi with your own Docker Hub repository name in the env section.
  5. Save the file.

Step 2: Understanding the Workflow

  1. Event Triggers:

    • The workflow triggers on two events:
      • A push event that modifies the workflow file or the project files.
      • A manual workflow_dispatch event for testing or deployment on demand.

  2. Environment Variables:

    • The workflow defines an env variable named DOCKER_IMAGE, which contains the name of the Docker image to be built and pushed.

  3. Steps in the Workflow:

    • Checkout Code: Pulls the latest code from the repository.
    • Build ASP.NET Web API: Builds the Web API project using the .NET CLI.
    • Build Local Docker Image: Builds a Docker image using the Dockerfile in the project directory.
    • List Docker Images: Lists all local Docker images for verification.
    • Log in to Docker Hub: Authenticates to Docker Hub using the secrets provided.
    • Tag Image: Tags the built image with latest for versioning.
    • Push Image to Docker Hub: Publishes the tagged image to your Docker Hub repository.

    These steps together ensure that the Web API is built, containerized, and published for use.

Step 3: Trigger the Workflow

  1. Commit and push the workflow file to your repository’s main branch with a descriptive commit message, e.g., “Add Docker image publishing workflow”.
  2. Navigate to the Actions tab in your GitHub repository.
  3. Locate the ASP.NET Web API Publish Docker Image workflow and click Run workflow to trigger it manually.

Step 4: Verify the Workflow Execution

  1. Monitor the workflow logs:
    • Verify the Build ASP.NET Weather Web API step completes successfully.
    • Confirm that the Docker image is built locally.
    • Ensure the image is tagged with latest and pushed to Docker Hub.
  2. After the workflow completes, log in to your Docker Hub account and verify that the image is listed in your repository.

Step 5: Pull and Test the Docker Image Locally

  1. On your local machine, pull the image from Docker Hub:

    docker pull prasadhonrao/aspnet-weather-webapi:latest

    Replace prasadhonrao/aspnet-weather-webapi with your own Docker Hub repository name.

  2. Run the Docker container:

    docker run -d -p 8080:80 prasadhonrao/aspnet-weather-webapi:latest

  3. Access the running application in your browser at http://localhost:8080 and test the Web API endpoints.

Summary

In this lab, you:

You can now deploy your ASP.NET Web API as a containerized application anywhere Docker is supported.

Additional Resources