Github Actions Basics

GitHub Actions is a powerful CI/CD and automation platform built into GitHub repositories. By defining workflow files directly in your project, you can automate builds, tests, deployments, and repository maintenance tasks without relying on external tools.

What Is GitHub Actions?

GitHub Actions lets you create workflows—collections of jobs and steps—that run in response to repository events like push, pull_request, schedule, and more.

With just a YAML file, you can trigger workflows on every pull request, run unit tests, and even deploy merged changes to production.

GitHub Actions provides first-class support for runners on Ubuntu, Windows, and macOS.

All infrastructure—server provisioning, auto-scaling, and environment maintenance—is handled by GitHub, so you can focus on writing workflows.

Beyond CI/CD: Repository Automation

While GitHub Actions shines for CI/CD—building, packaging, and deploying code—it also responds to many repository events, such as issues, pull requests, releases, and registry packages:

For example, on a new pull request you could automatically:

• Post a welcome comment
• Apply labels based on modified files
• Assign reviewers or assignees

These patterns can extend to issues (opened, labeled), releases (published), and package registry events.

Core Concepts

Workflows

A workflow is defined by a YAML file in your repository’s .github/workflows/ directory. You can have multiple workflows, each triggered by different events:

# .github/workflows/ci.yml
name: My Awesome App
on:
  push:
  pull_request:
    branches: [ main ]
  schedule:
    - cron: '0 0 * * *'

Jobs and Steps

A workflow runs one or more jobs, each made up of sequential steps. Jobs run on runners—either GitHub-hosted VMs or your own self-hosted machines.

jobs:
  unit-testing:
    name: Unit Testing
    strategy:
      matrix:
        os: [ubuntu-latest, macos-latest, windows-latest]
        node-version: [14, 16]
    runs-on: ${{ matrix.os }}
    steps:
      - name: Checkout code
        uses: actions/checkout@v3

      - name: Set up Node.js ${{ matrix.node-version }}
        uses: actions/setup-node@v3
        with:
          node-version: ${{ matrix.node-version }}

      - name: Install dependencies
        run: npm ci

      - name: Run tests
        run: npm test

In this example:

1. The workflow triggers on push and pull_request.
2. A matrix strategy runs tests across multiple OS and Node.js versions.
3. Each runner checks out code, installs Node.js, installs dependencies, and executes npm test.

Hosted Runners

GitHub-managed runners are provisioned on-demand (Linux, Windows on Azure, and macOS on GitHub’s cloud). Each job gets a clean VM:

After a run completes, you can inspect logs, review step details, and download build artifacts from the Actions tab.

Runner Types: GitHub-Hosted vs. Self-Hosted

Self-hosted runners let you use your own hardware, install custom software, or target GPUs. Compare the two options:

This article covered the essentials of GitHub Actions: defining workflows, splitting tasks into jobs and steps, leveraging matrix builds, and choosing the right runner. For more details, see the GitHub Actions documentation.