II. Continuous Integration / Continuous Delivery

In order to start with CI/CD using GitHub Actions one just needs to add a config file to the repository under .github/workflows folder. You can find my configuration here:

https://github.com/olegpolivin/FizzBuzz-CI-CD/blob/main/.github/workflows/ci.yml

Basic example

The most basic configuration file might be the following one:

# This workflow will install Python dependencies, run tests and lint with a variety of Python versions
# For more information see: https://help.github.com/actions/language-and-framework-guides/using-python-with-github-actions

name: CI

on:
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]
jobs:
  build:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        python-version: [3.7]
    steps:
    - uses: actions/checkout@v2
    - name: Set up Python
      uses: actions/setup-python@v2
      with:
        python-version: ${{ matrix.python-version }}
    # You can test your matrix by printing the current Python version
    - name: Display Python version
      run: python -c "import sys; print(sys.version)"

It is not doing anything important. It makes use of Github Actions and the only thing it does is printing a python version, in my case 3.7. Creating a pull request will run the script above. Pull request will always pass all checks, because the script cheks nothing. However, the setting above is enough for Github to prevent from pushing directly to the main branch. We just need to add a rule for a branch. Later we will add code formatters and a linter to this script.

Set up a rule for your branch

It is necessary just to add some modifications to the Settings -> Branches -> Rules. See what’s new:

Notice that build (3.7) has appeared among status checks. This corresponds to the name of the job (build) and python version 3.7. I made a small modification to the README.md file, and let’s see if I can push it now to the main branch. Here is the error I get:

Total 3 (delta 1), reused 0 (delta 0)
remote: Resolving deltas: 100% (1/1), completed with 1 local object.
remote: error: GH006: Protected branch update failed for refs/heads/main.
remote: error: Required status check "build (3.7)" is expected.
To https://github.com/olegpolivin/FizzBuzz-CI-CD.git
! [remote rejected] main -> main (protected branch hook declined)
error: failed to push some refs to 'https://github.com/olegpolivin/FizzBuzz-CI-CD.git'

Nice! The commit is rejected because a required status check is needed. Therefore, let’s push to a new branch. Locally, let’s create a new branch

git checkout -b dev
git push origin dev

A new branch called dev is created on the remote repository. What’s left is to create a pull request, and merge it to the main branch.

It becomes possible to merge after all checks are run:

We would like to introduce actions or tests to be performed, before the pull request is ready to be approved, so let’s provide code that will be actually checked. We will consider solving the FizzBuzz problem, see the next section III. FizzBuzz.