# 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 }}"