GitHub Actions

GitHub Actions is GitHub's built-in CI/CD platform. It allows you to automate workflows directly from your repository — building, testing, and deploying code in response to events like pushes, pull requests, and releases.

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Why GitHub Actions?

• Integrated — lives inside your GitHub repository, no external service to configure
• Free for public repos — unlimited minutes for open-source projects
• Marketplace — thousands of pre-built actions for common tasks
• Matrix builds — test across multiple OS/language versions easily
• Secrets management — built-in encrypted secret storage
• Self-hosted runners — run on your own infrastructure if needed

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Core Concepts

Concept	Description
Workflow	A YAML file in .github/workflows/ that defines automation
Event	A trigger that starts a workflow (push, PR, schedule, manual)
Job	A set of steps that run on a single runner
Step	An individual task — either a shell command or an action
Action	A reusable unit of code (from Marketplace or custom)
Runner	The machine (VM) that executes a job

Hierarchy

graph TD
  W["Workflow (.github/workflows/ci.yml)"] --> EV["Event: push to main"]
  W --> JB["Job: build"]
  W --> JD["Job: deploy"]
  JB --> B1["Step 1: Checkout code"]
  JB --> B2["Step 2: Install dependencies"]
  JB --> B3["Step 3: Run tests"]
  JB --> B4["Step 4: Build"]
  JD --> D1["Step 1: Checkout code"]
  JD --> D2["Step 2: Deploy to production"]

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Your First Workflow

Create a file at .github/workflows/ci.yml:

name: CI

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

jobs:
  build-and-test:
    runs-on: ubuntu-latest

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

      - name: Set up Node.js
        uses: actions/setup-node@v4
        with:
          node-version: 20
          cache: 'npm'

      - name: Install dependencies
        run: npm ci

      - name: Lint
        run: npm run lint

      - name: Type check
        run: npm run typecheck

      - name: Run tests
        run: npm test -- --coverage

      - name: Build
        run: npm run build

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Events (Triggers)

Event	Example	Use Case
push	on: push	Run on every push
pull_request	on: pull_request	Run on PR events
schedule	on: schedule: cron: '0 2 * * *'	Nightly builds
workflow_dispatch	on: workflow_dispatch	Manual trigger
release	on: release: types: [published]	Publish on release
repository_dispatch	on: repository_dispatch	External webhook trigger

Filtering Events

on:
  push:
    branches: [main, develop]
    paths:
      - 'src/**'
      - 'package.json'
    paths-ignore:
      - 'docs/**'
      - '*.md'

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Runners