wiki/notebook/cloud.github-actions.org

GitHub Actions

• Examples
  • Python version of an installation
  • Docker container integration
  • Building a Nix binary cache
  • Multiple jobs with matrix

• a CI/CD tool integrated into GitHub
• it is free for public repos but limited time per month for private repos

• focused into creating workflows which can be separate and applied in different contexts

  • a workflow is activated from an event
  • stored in .github/workflows in the remote repo
• each workflow can run a job which are composed of steps
• each step make uses an action which is basically a script; it can interact with the repo or do something else entirely without ever touching it
• you can use already defined actions or with your own
• if you want to explore other options, the GitHub marketplace allows searching for various third-party actions

Examples

With GitHub Actions being a massive ecosystem of integrations as of 2021-07-05, we have to find some examples in the worldwide community repos from there.

Python version of an installation

The following block is a minimal example checking the Python version in the installation.

name: Python version
on: [push]
jobs:
  check-python-version:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-python@v2
      - run: python --version

Docker container integration

In this case, we'll push an image to docker.io registry.

name: Docker build image
on: [push]
jobs:
    docker:
        runs-on: ubuntu-latest
        steps:
            - name: Checkout
              uses: actions/checkout@v2
            - name: Set up QEMU
              uses: docker/setup-qemu-action@v1
            - name: Setup Docker Buildx
              uses: docker/setup-buildx-action@v1
            - name: Login to DockerHub
              uses: docker/login-action@v1
              with:
                  username: ${{ secrets.DOCKERHUB_USERNAME }}
                  password: ${{ secrets.DOCKERHUB_TOKEN }}
            - name: Build and push
              id: docker_build
              uses: docker/build-push-action@v2
              with:
                  push: true
                  tags: ${{ secrets.DOCKERHUB_USERNAME }}/python-helloworld:latest
                  platforms: linux/amd64,linux/arm64
            - name: Image digest
              run: echo ${{ steps.docker_build.outputs.digest }}

Building a Nix binary cache

We'll use Cachix as our binary cache service. This makes it easier to setup and distribute your own project built with Nix package manager.

name: "Push packages into Cachix cache"
on:
  pull_request:
  push:
jobs:
  tests:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v2.3.4
    - uses: cachix/install-nix-action@v13
      with:
        nix_path: nixpkgs=channel:nixos-unstable
    - uses: cachix/cachix-action@v10
      with:
        name: mycache
        signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
    - run: nix-build
    - run: nix-shell --run "echo OK"

Multiple jobs with matrix

We'll use the GitHub Actions workflow file from the NUR template. It is somewhat complex and it is doing a fine job showcasing some of GitHub Actions features.

name: "Build and populate cache"
on:
  pull_request:
  push:
  schedule:
    # rebuild everyday at 2:51
    # TIP: Choose a random time here so not all repositories are build at once:
    # https://www.random.org/clock-times/?num=1&earliest=01%3A00&latest=08%3A00&interval=5&format=html&rnd=new
    - cron:  '27 4 * * *'
jobs:
  tests:
    strategy:
      matrix:
        # Set this to notify the global nur package registry that changes are
        # available.
        #
        # The repo name as used in
        # https://github.com/nix-community/NUR/blob/master/repos.json
        nurRepo:
          - '<YOUR_NUR_REPO>'
        # Set this to cache your build results in cachix for faster builds
        # in CI and for everyone who uses your cache.
        #
        # Format: Your cachix cache host name without the ".cachix.org" suffix.
        # Example: mycache (for mycache.cachix.org)
        #
        # For this to work, you also need to set the CACHIX_SIGNING_KEY secret
        # in your repository settings in Github found at https://github.com/<your_githubname>/nur-packages/settings/secrets
        cachixName:
          - '<YOUR_CACHIX_NAME>'
        nixPath:
          - nixpkgs=channel:nixos-unstable
          - nixpkgs=channel:nixpkgs-unstable
          - nixpkgs=channel:nixos-21.05
    runs-on: ubuntu-latest
    steps:
    - name: Checkout repository
      uses: actions/checkout@v2.3.4
    - name: Install nix
      uses: cachix/install-nix-action@v13
      with:
        nix_path: "${{ matrix.nixPath }}"
    - name: Show nixpkgs version
      run: nix-instantiate --eval -E '(import <nixpkgs> {}).lib.version'
    - name: Setup cachix
      uses: cachix/cachix-action@v10
      if: ${{ matrix.cachixName != '<YOUR_CACHIX_NAME>' }}
      with:
        name: ${{ matrix.cachixName }}
        signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
    - name: Check evaluation
      run: |
        nix-env -f . -qa \* --meta --xml \
          --allowed-uris https://static.rust-lang.org \
          --option restrict-eval true \
          --option allow-import-from-derivation true \
          --drv-path --show-trace \
          -I nixpkgs=$(nix-instantiate --find-file nixpkgs) \
          -I $PWD        
    - name: Build nix packages
      # TODO switch to default nixpkgs channel once nix-build-uncached 1.0.0 is in stable
      run: nix run -I 'nixpkgs=channel:nixos-unstable' nixpkgs.nix-build-uncached -c nix-build-uncached ci.nix -A cacheOutputs
    - name: Trigger NUR update
      if: ${{ matrix.nurRepo != <YOUR_NUR_REPO>' }}
      run: curl -XPOST "https://nur-update.herokuapp.com/update?repo=${{ matrix.nurRepo }}"