GitHub Actions

Date: 2021-06-20 18:58:48 +08:00Date modified: 2022-06-19 11:46:41 +08:00

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

Ecosystem

there is also a detailed guide in introducing the overall concept
the workflow allows you to create build artifacts; you have fine-grained control such as letting you upload certain files to be artifacts and downloading them after a workflow run; it also enables sharing of data between jobs
it can make automated releases like what I have done with one of my projects
it can create automated Git commits with Git Auto Commit; combine with the ability to set schedules, you can create an automatic sync following a project
otherwise, you can also create automated release but have to go through a merge request; for example, this is how Simple Icons maintain their releases

Actions

each of the job is mostly built with the actions; the job can be controlled further through the workflow file; see the Workflow Syntax for more information
related information such as the current branch, runners specifics, and so forth are stored in Contexts
like previously mentioned, you can search these actions in GitHub's marketplace
the actions are primarily defined with actions.yml from the root which can serve as a documentation for the parameters

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

GitHub workflows can make use of containers for easier delivering of dependencies and reproducing the development environment (among other things). This includes...

GitHub's own container registry,
using a container to be used in a workflow which is nice for building for multiple operating systems (e.g., multiple Linux distros)
service containers to make use of tools to your workflow,
and even publishing containers to a registry from a workflow.

In this example, we'll push an image to docker.io registry. Be sure to have the necessary credentials and set it to the workflow environment to successfully run this workflow.

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 which has a free 10GB space (as of 2022-06-19). 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"

Building packages in multiple architectures

This makes use of job matrix allowing to easily create similar workflows with different configurations.

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:
    - cron:  '27 4 * * *'
jobs:
  tests:
    strategy:
      matrix:
        nurRepo:
          - '<YOUR_NUR_REPO>'
        cachixName:
          - '<YOUR_CACHIX_NAME>'
        nixPath:
          - nixpkgs=channel:nixos-unstable
          - nixpkgs=channel:nixpkgs-unstable
    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
      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 }}"