GitHub Actions in 10 Minutes

GitHub Actions is a free CI/CD system built into GitHub. Every time you push, it can automatically:

• run your tests,
• build your Docker image,
• deploy to production.

Anatomy of a workflow

Place this file in your repo at .github/workflows/ci.yml:

name: CI

on:                        # when to run
  push: { branches: [main] }
  pull_request:

jobs:
  test:                    # a job is a set of steps that run on one machine
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with: { node-version: 20, cache: yarn }
      - run: yarn install --frozen-lockfile
      - run: yarn lint
      - run: yarn test --coverage

The four building blocks

Word	Meaning
Workflow	The whole YAML file.
Job	A group of steps on one machine (runs-on).
Step	A single command or a pre-built uses: action.
Runner	The virtual machine that runs the job.

Adding secrets

Go to Repo → Settings → Secrets and variables → Actions and add AWS_ACCESS_KEY_ID. Use it as:

env:
  AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}

Beginner tips

• Cache dependencies with actions/setup-node's cache: yarn — huge speed win.
• Split slow jobs into matrix builds to run Node 18, 20, 22 in parallel.
• Use the Marketplace — someone probably wrote the action you need.

Real-world example

Push code → tests run in 2 minutes → if green, a second job builds a Docker image and pushes to ECR → a third job deploys to staging. All from one file, all free (for public repos).