GitHub Actions (Basic Intro)

Set up your first CI workflow that runs automatically on pull requests and verifies code quality before merge.

Simple Explanation (ELI5)

GitHub Actions is a robot teammate. When someone opens a PR, it automatically runs your checklist: install dependencies, run tests, and tell you pass/fail.

Technical Explanation

A workflow is YAML under .github/workflows/. It has triggers (on), jobs, and steps. Jobs run on runners (virtual machines). CI status integrates with branch protection so only passing PRs can merge.

Visual: Basic CI Flow

Hands-on: First Workflow

name: ci-basic
on:
  pull_request:
    branches: ["main"]
  push:
    branches: ["main"]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v4

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

      - name: Install
        run: npm ci

      - name: Lint
        run: npm run lint --if-present

      - name: Test
        run: npm test -- --ci

# Create workflow directory
mkdir -p .github/workflows

# Save YAML as .github/workflows/ci-basic.yml
# Commit and push
git add .github/workflows/ci-basic.yml
git commit -m "ci: add basic GitHub Actions workflow"
git push origin feature/ci-basic

Debugging Scenarios

• Workflow not running: Confirm trigger branch names match exactly.
• npm ci fails: Lockfile mismatch or missing package lock.
• Action version errors: Pin supported action tags (@v4, not floating @main).
• Permission denied: Check default GITHUB_TOKEN permissions in repo settings.

Real-world Use Case

After introducing required CI checks on PRs, a product team prevented untested hotfixes from entering main. Defect escape rate dropped because failing tests blocked merges automatically.

Interview Questions

Summary

GitHub Actions provides immediate CI value with minimal setup. A simple PR-triggered workflow can dramatically increase merge confidence and team consistency.