GitHub Actions Introduction

GitHub Actions automates workflows directly in your repository. Build, test, and deploy code; respond to events; automate repetitive tasks—all in GitHub.

What are GitHub Actions?

Actions are automated workflows triggered by events:

Event (push, PR, schedule, etc.)
        ↓
    Workflow runs
        ↓
    Jobs execute
        ↓
    Steps run commands

Key Concepts

Workflows

A configurable automated process:

• Defined in .github/workflows/*.yml
• Triggered by events
• Contains one or more jobs

Events

What triggers a workflow:

• push: Code pushed
• pull_request: PR opened/updated
• schedule: Cron schedule
• workflow_dispatch: Manual trigger
• issues: Issue created/updated
• Many more...

Jobs

A set of steps that run on the same runner:

• Jobs run in parallel by default
• Can set dependencies between jobs

Steps

Individual tasks in a job:

• Run commands
• Use actions (reusable units)

Actions

Reusable units of code:

• Official: actions/checkout, actions/setup-node
• Community: Thousands available
• Custom: Create your own

Your First Workflow

Create .github/workflows/ci.yml:

name: CI

on:
  push:
    branches: [main]
  pull_request:
    branches: [main]

jobs:
  build:
    runs-on: ubuntu-latest

    steps:
      - name: Checkout code
        uses: actions/checkout@v4

      - name: Setup Node.js
        uses: actions/setup-node@v4
        with:
          node-version: '20'

      - name: Install dependencies
        run: npm ci

      - name: Run tests
        run: npm test

      - name: Build
        run: npm run build

Workflow Syntax

Triggers (on)

# Push to specific branches
on:
  push:
    branches: [main, develop]

# Pull requests
on:
  pull_request:
    branches: [main]

# Scheduled (cron)
on:
  schedule:
    - cron: '0 0 * * *'  # Daily at midnight

# Manual trigger
on:
  workflow_dispatch:

# Multiple events
on:
  push:
    branches: [main]
  pull_request:
  schedule:
    - cron: '0 0 * * 0'  # Weekly

Jobs

jobs:
  # Job ID (any name)
  build:
    runs-on: ubuntu-latest
    steps:
      - run: echo "Building..."

  test:
    runs-on: ubuntu-latest
    needs: build  # Wait for build to complete
    steps:
      - run: echo "Testing..."

  deploy:
    runs-on: ubuntu-latest
    needs: [build, test]  # Wait for both
    steps:
      - run: echo "Deploying..."

Steps

steps:
  # Run shell command
  - run: npm install

  # Use an action
  - uses: actions/checkout@v4

  # Named step with action and inputs
  - name: Setup Node
    uses: actions/setup-node@v4
    with:
      node-version: '20'

  # Multi-line command
  - name: Run script
    run: |
      echo "Line 1"
      echo "Line 2"
      npm test

Common Actions

actions/checkout

Clone your repository:

- uses: actions/checkout@v4
  with:
    fetch-depth: 0  # Full history (for tags, etc.)

actions/setup-node

Set up Node.js:

- uses: actions/setup-node@v4
  with:
    node-version: '20'
    cache: 'npm'  # Cache dependencies

actions/cache

Cache dependencies:

- uses: actions/cache@v4
  with:
    path: ~/.npm
    key: npm-${{ hashFiles('package-lock.json') }}

actions/upload-artifact

Save files between jobs:

- uses: actions/upload-artifact@v4
  with:
    name: build
    path: dist/

Environment Variables

env:
  # Workflow level
  NODE_ENV: production

jobs:
  build:
    env:
      # Job level
      CI: true

    steps:
      - name: Build
        env:
          # Step level
          API_URL: ${{ secrets.API_URL }}
        run: npm run build

Secrets

Store sensitive data:

1. Go to Settings → Secrets and variables → Actions
2. Add secret
3. Use in workflow:

steps:
  - name: Deploy
    env:
      API_KEY: ${{ secrets.API_KEY }}
    run: ./deploy.sh

Matrix Builds

Test across multiple versions:

jobs:
  test:
    strategy:
      matrix:
        node: [18, 20, 22]
        os: [ubuntu-latest, windows-latest]

    runs-on: ${{ matrix.os }}

    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: ${{ matrix.node }}
      - run: npm test

This creates 6 jobs (3 Node versions × 2 OS).

Conditional Execution

steps:
  # Only on push (not PR)
  - run: ./deploy.sh
    if: github.event_name == 'push'

  # Only on main branch
  - run: ./release.sh
    if: github.ref == 'refs/heads/main'

  # Only if previous step succeeded
  - run: ./notify-success.sh
    if: success()

  # Only if previous step failed
  - run: ./notify-failure.sh
    if: failure()

  # Always run
  - run: ./cleanup.sh
    if: always()

Common Workflow Examples

CI Pipeline

name: CI
on: [push, pull_request]

jobs:
  lint:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
      - run: npm ci
      - run: npm run lint

  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
      - run: npm ci
      - run: npm test

  build:
    needs: [lint, test]
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
      - run: npm ci
      - run: npm run build

Deploy on Release

name: Deploy
on:
  release:
    types: [published]

jobs:
  deploy:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: npm ci
      - run: npm run build
      - run: ./deploy.sh
        env:
          DEPLOY_KEY: ${{ secrets.DEPLOY_KEY }}

Viewing Workflow Runs

1. Go to "Actions" tab
2. Select workflow
3. Click run to see details
4. View logs for each step

Summary

• Actions automate workflows in your repository
• Workflows are defined in YAML files
• Triggered by events (push, PR, schedule, etc.)
• Jobs contain steps that run commands or actions
• Use matrix builds for cross-platform testing
• Store sensitive data in secrets
• View runs in the Actions tab

In the next lesson, we'll learn about GitHub Releases.