This is a simple example of how to use GitHub Actions to build and push a docker image to a container registry.

Prerequisites

• A docker file exists for the project you want to build and push.
• A GitHub repository exists for the project.
• A container registry exists to push the image to.
• A docker registry's username and password (in GuitHub Secrets)

For this project I started with the basic .NET Core ASP.NET project and the default Dockerfile created by Rider.

Dockerfile

This Dockerfile is a multi-stage build that builds the project and then copies the output to a runtime image.

For this proect, as I use TailwindCSS, I also need to install Node.js and run the TailwindCSS build command.

# Install Node.js v20.x
RUN apt-get update && apt-get install -y curl \
    && curl -fsSL https://deb.nodesource.com/setup_20.x -o nodesource_setup.sh \
    && bash nodesource_setup.sh \
    && apt-get install -y nodejs \
    && rm -f nodesource_setup.sh \
    && rm -rf /var/lib/apt/lists/*

This downloads the latest (at the time of writing) version of Node.js and installs it into the build image.

Later in the file

FROM mcr.microsoft.com/dotnet/aspnet:8.0 AS base
USER $APP_UID
WORKDIR /app
EXPOSE 8080
EXPOSE 8081

FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build
ARG BUILD_CONFIGURATION=Release

# Install Node.js v20.x
RUN apt-get update && apt-get install -y curl \
    && curl -fsSL https://deb.nodesource.com/setup_20.x -o nodesource_setup.sh \
    && bash nodesource_setup.sh \
    && apt-get install -y nodejs \
    && rm -f nodesource_setup.sh \
    && rm -rf /var/lib/apt/lists/*

WORKDIR /src
COPY ["Mostlylucid/Mostlylucid.csproj", "Mostlylucid/"]
RUN dotnet restore "Mostlylucid/Mostlylucid.csproj"
COPY . .
WORKDIR "/src/Mostlylucid"

# Copy package.json and package-lock.json and install npm dependencies
COPY package*.json ./
RUN npm install

# Ensure npm-run-all is available and install npm dependencies
RUN npm --version
RUN npx tailwindcss -i ./src/css/main.css -o ./wwwroot/css/dist/main.css

RUN dotnet build "Mostlylucid.csproj" -c $BUILD_CONFIGURATION -o /app/build


FROM build AS publish
RUN dotnet publish "Mostlylucid.csproj" -c $BUILD_CONFIGURATION -o /app/publish /p:UseAppHost=false

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "Mostlylucid.dll"]

GitHub Actions

The GitHub Action for this site is a simple build and push action that is triggered on a push to the main branch. https://github.com/scottgal/mostlylucidweb/blob/main/.github/workflows/docker-image.yml

This action checks out the repository, logs into Docker Hub, sets up Docker Buildx, caches the Docker layers, builds and tags the Docker image, and then pushes the image to Docker Hub.

In the docker compose file

name: Docker Image CI

on:
  push:
    branches: [ "main" ]
  pull_request:
    branches: [ "main" ]

jobs:
  build-and-push:
    runs-on: ubuntu-latest

    steps:
    - name: Check out the repository
      uses: actions/checkout@v4

    - name: Log in to Docker Hub
      run: echo "${{ secrets.DOCKER_HUB_ACCESS_TOKEN }}" | docker login -u "${{ secrets.DOCKER_HUB_USER_NAME }}" --password-stdin

    - name: Set up Docker Buildx
      uses: docker/setup-buildx-action@v2

    - name: Cache Docker layers
      uses: actions/cache@v3
      with:
        path: /tmp/.buildx-cache
        key: ${{ runner.os }}-buildx-${{ github.sha }}
        restore-keys: |
          ${{ runner.os }}-buildx-

    - name: Build and tag the Docker image
      id: build
      run: |
        TIMESTAMP=$(date +%s)
        echo "TIMESTAMP=$TIMESTAMP" >> $GITHUB_ENV
        docker build . --file Mostlylucid/Dockerfile --tag ${{ secrets.DOCKER_HUB_USER_NAME }}/mostlylucid:latest --tag ${{ secrets.DOCKER_HUB_USER_NAME }}/mostlylucid:$TIMESTAMP

    - name: Push the Docker image to Docker Hub
      run: |
        docker push ${{ secrets.DOCKER_HUB_USER_NAME }}/mostlylucid:latest
        docker push ${{ secrets.DOCKER_HUB_USER_NAME }}/mostlylucid:${{ env.TIMESTAMP }}