Now let’s dissect a workflow file part by part. Once you can read each section, you can build almost any pipeline you need.

🎯 Learning Objectives

By the end of this lesson you will:

• Control when a workflow runs with triggers
• Structure jobs and steps correctly
• Run a job across multiple versions with a matrix
• Speed up runs with caching

Triggers — the on Key

The on key decides what events start the workflow:

on:
push:
  branches: [main]           # only pushes to main
pull_request:
  branches: [main]           # PRs targeting main
schedule:
  - cron: "0 6 * * *"        # every day at 06:00 UTC
workflow_dispatch:           # a manual "Run" button

Jobs and Steps

A workflow has one or more jobs; each job has ordered steps:

jobs:
test:
  runs-on: ubuntu-latest       # the runner OS
  steps:
    - uses: actions/checkout@v4
    - uses: actions/setup-node@v4
      with:
        node-version: 20
    - run: npm ci               # install
    - run: npm test             # test

By default, jobs run in parallel. Steps within a job run in order, sharing the same runner and filesystem.

Job Dependencies

Use needs to make one job wait for another — essential for build → deploy ordering:

jobs:
build:
  runs-on: ubuntu-latest
  steps:
    - run: echo "building"

deploy:
  needs: build            # only runs if build succeeds
  runs-on: ubuntu-latest
  steps:
    - run: echo "deploying"

Matrix Builds

A matrix runs the same job across multiple configurations in parallel — perfect for testing several language versions:

jobs:
test:
  runs-on: ubuntu-latest
  strategy:
    matrix:
      node: [18, 20, 22]
  steps:
    - uses: actions/checkout@v4
    - uses: actions/setup-node@v4
      with:
        node-version: ${{ matrix.node }}
    - run: npm test

This automatically creates three parallel jobs — one each for Node 18, 20, and 22.

Caching for Speed

Reinstalling dependencies every run is slow. Cache them to speed things up dramatically:

- uses: actions/setup-node@v4
with:
  node-version: 20
  cache: 'npm'          # cache the npm dependency store

🧪 Hands-on Lab

on:
push: { branches: [main] }
pull_request: {}
jobs:
test:
  runs-on: ubuntu-latest
  strategy:
    matrix: { node: [20, 22] }
  steps:
    - uses: actions/checkout@v4
    - uses: actions/setup-node@v4
      with: { node-version: "${{ matrix.node }}", cache: npm }
    - run: npm ci && npm test
deploy:
  needs: test
  runs-on: ubuntu-latest
  steps:
    - run: echo "All matrix jobs passed — deploying"

🧠 Knowledge Check

💼 Interview Preparation

Summary

You can now read and write every part of a workflow: triggers, jobs, steps, needs dependencies, matrix builds, and caching. Next, you’ll assemble these into a complete build-and-test CI pipeline for a real project.