Skip to main content

Starter Notes

Updated Jul 13, 2021 ·

Overview​

GitHub Actions (GHA) automates software workflows like building, testing, and deploying code.

  • Built-in CI/CD system in GitHub
  • Automates repetitive development tasks
  • Runs directly inside GitHub repositories

Just like a car assembly line has workers performing tasks step by step, GHA automates software development in an organized flow.

GHA Components​

Event​

An event is what triggers a workflow in GitHub Actions.

  • Happens when someone pushes code, opens a pull request, or creates an issue
  • Can also be triggered manually or on a schedule
on: push  # Triggers workflow when code is pushed

Workflow​

A workflow is a set of automated tasks defined in a YAML file.

  • Stored in .github/workflows/
  • Can contain multiple jobs
  • Runs when triggered by an event

Example: A workflow to test and deploy code:

name: CI Workflow
on: push
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - run: echo "Running tests"

Steps and Actions​

A step is an individual task within a job. An action is a reusable task inside a step.

  • Steps execute in order within a job
  • Actions simplify complex tasks (e.g., checking out code)

Example: Running a script after checking out code:

steps:
  - uses: actions/checkout@v3  # Action to get the code
  - run: python script.py       # Step to run the script

Jobs and Runners​

A job is a collection of steps, and a runner is the machine that executes them.

  • Jobs run independently, but dependencies can be set
  • Runners can be Linux, macOS, or Windows

Example: Two jobs running in parallel:

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - run: echo "Building the app"
  test:
    runs-on: ubuntu-latest
    steps:
      - run: echo "Testing the app"

A Simple GHA Workflow​

A push event triggers a workflow with a job that runs on Ubuntu.

  • Step 1: Checkout repository
  • Step 2: Run a Python script

Example:

name: Simple Workflow
on: push
jobs:
  example-job:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - run: python script.py

Putting It All Together​

A GitHub Actions workflow consists of:

  1. Events (trigger the workflow)
  2. Workflows (contain jobs)
  3. Jobs (contain steps)
  4. Steps (run scripts or actions)
  5. Runners (execute jobs)

An example flow:

  • A push triggers a workflow
  • The workflow runs jobs in parallel
  • Jobs contain steps like scripts or actions
  • Outputs (artifacts) can be generated if needed

Multiline Strings in YAML​

YAML supports multiline strings using block scalar formats. These formats help keep line breaks and indentation intact, making them useful for configurations, logs, and CI/CD scripts.

  • Two styles: Literal (|) and Folded (>)
  • Three chomping indicators: Clip (default), Strip (-), Keep (+)

For more information, please see YAML data format.