GitHub Actions — Reusable Workflows & Matrices

Also Known As

TL;DR

Explanation

Advanced GitHub Actions: Reusable workflows (workflow_call trigger) — define once, call from multiple repos; matrix strategy — test across multiple PHP versions, OS, and dependency versions in parallel; composite actions — bundle multiple steps into a single reusable action; environments with protection rules — require approvals before deploying to production; concurrency groups — cancel superseded runs on the same branch; job dependencies (needs:) — sequential or conditional pipelines; OIDC authentication — exchange GitHub token for cloud provider credentials without storing secrets.

Common Misconception

Why It Matters

Common Mistakes

• Storing cloud credentials as repository secrets instead of using OIDC — static credentials that never expire.
• No concurrency groups — every push triggers a new run, queue piles up.
• Matrix without fail-fast: false — one matrix failure cancels all siblings.
• Pinning Actions to a mutable tag (v3) instead of a commit SHA — supply chain risk.

Code Examples

# Duplicated across 20 repos — maintenance nightmare:
# .github/workflows/ci.yml (same in every repo):
name: CI
on: [push]
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v4
    - run: composer install
    - run: vendor/bin/phpunit
# Security scan added? Update all 20 repos manually.

# Reusable workflow — org/.github/workflows/php-ci.yml:
on:
  workflow_call:
    inputs:
      php-version: {type: string, default: '8.3'}
jobs:
  test:
    strategy:
      matrix:
        php: ['8.1', '8.2', '8.3']
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # SHA pin
    - uses: shivammathur/setup-php@v2
      with: {php-version: ${{ matrix.php }}}
    - run: composer install
    - run: composer audit  # Security in shared workflow
    - run: vendor/bin/phpunit

# Each repo just calls it:
# .github/workflows/ci.yml:
jobs:
  ci:
    uses: org/.github/workflows/php-ci.yml@main

References

• ↗ https://docs.github.com/en/actions/using-workflows/reusing-workflows

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