CI Optimization Specialist

Quick Start

This skill optimizes GitHub Actions workflows for:

• Test sharding: Parallel test execution across multiple runners

• Caching: pnpm store, Playwright browsers, Vite build cache

• Workflow optimization: Job dependencies and concurrency

When to Use

• CI execution time exceeds 10-15 minutes

• GitHub Actions costs too high

• Need faster developer feedback loops

• Tests not parallelized

Test Sharding Setup

Basic Pattern (Automatic Distribution)

Add matrix strategy to .github/workflows/ci.yml :

e2e-tests: name: 🧪 E2E Tests [Shard ${{ matrix.shard }}/3] runs-on: ubuntu-latest timeout-minutes: 30 strategy: fail-fast: false matrix: shard: [1, 2, 3] steps: - name: Run Playwright tests run: pnpm exec playwright test --shard=${{ matrix.shard }}/3 env: CI: true

Expected improvement: 60-65% faster for 3 shards

Advanced Pattern (Manual Distribution)

For unbalanced test suites, manually distribute by duration:

matrix: include: - shard: 1 pattern: 'ai-generation|project-management' # Heavy tests - shard: 2 pattern: 'project-wizard|settings|publishing' # Medium tests - shard: 3 pattern: 'world-building|versioning|mock-validation' # Light tests

In step:

run: pnpm exec playwright test --grep "${{ matrix.pattern }}"

Critical Caching Patterns

pnpm Store Cache

ALWAYS cache pnpm store to avoid re-downloading packages:

• name: Get pnpm store directory id: pnpm-cache shell: bash run: echo "STORE_PATH=$(pnpm store path)" >> $GITHUB_OUTPUT

• name: Setup pnpm cache uses: actions/cache@v4 with: path: ${{ steps.pnpm-cache.outputs.STORE_PATH }} key: ${{ runner.os }}-pnpm-store-${{ hashFiles('**/pnpm-lock.yaml') }} restore-keys: | ${{ runner.os }}-pnpm-store-

Playwright Browsers Cache

Cache 500MB+ browser binaries:

• name: Cache Playwright browsers uses: actions/cache@v4 id: playwright-cache with: path: ~/.cache/ms-playwright key: ${{ runner.os }}-playwright-${{ hashFiles('**/pnpm-lock.yaml') }}

• name: Install Playwright browsers if: steps.playwright-cache.outputs.cache-hit != 'true' run: pnpm exec playwright install --with-deps chromium

• name: Install Playwright system dependencies if: steps.playwright-cache.outputs.cache-hit == 'true' run: pnpm exec playwright install-deps chromium

Vite Build Cache

For monorepos or frequent builds:

• name: Cache Vite build uses: actions/cache@v4 with: path: | dist/ node_modules/.vite/ key: ${{ runner.os }}-vite-${{ hashFiles('src/**', 'vite.config.ts') }}

Workflow Optimization

Job Dependencies

Use needs to control execution flow:

jobs: build-and-test: runs-on: ubuntu-latest steps: - name: Build run: pnpm run build - name: Run unit tests run: pnpm test

e2e-tests: needs: build-and-test # Wait for build to complete runs-on: ubuntu-latest strategy: matrix: shard: [1, 2, 3] steps: - name: Run E2E tests run: pnpm exec playwright test --shard=${{ matrix.shard }}/3

Concurrency Control

Prevent multiple runs on same branch:

concurrency: group: ${{ github.workflow }}-${{ github.ref }} cancel-in-progress: true

Artifact Management

Per-Shard Artifacts

Upload test reports from each shard:

• name: Upload Playwright report if: always() uses: actions/upload-artifact@v4 with: name: playwright-report-shard-${{ matrix.shard }}-${{ github.sha }} path: playwright-report/ retention-days: 7 compression-level: 6

Artifact Cleanup

Set short retention for test reports to reduce storage costs:

retention-days: 7 # Default is 90 days compression-level: 6 # Compress to reduce storage

Performance Monitoring

Expected Benchmarks

Optimization Before After Improvement

Test sharding (3 shards) 27 min 9-10 min 60-65%

pnpm cache hit 2-3 min 10-15s 85-90%

Playwright cache hit 1-2 min 5-10s 90-95%

Vite build cache 1-2 min 5-10s 90-95%

Regression Detection

Set timeout thresholds as guardrails:

timeout-minutes: 30 # Fail if shard exceeds 30 minutes

Monitor shard execution times and rebalance if one shard consistently exceeds others by >2 minutes.

Optimization Workflow

Phase 1: Baseline

• Record current CI execution times

• Identify slowest jobs

• Measure cache hit rates (check Actions logs)

Phase 2: Implement Caching

• Add pnpm store cache (highest impact)

• Add Playwright browser cache

• Add build caches if applicable

• Verify cache keys work correctly

Phase 3: Implement Sharding

• Calculate optimal shard count (target 3-5 min per shard)

• Add matrix strategy to workflow

• Test locally: playwright test --shard=1/3

• Monitor shard balance in CI

Phase 4: Monitor & Adjust

• Track execution times over 5-10 runs

• Identify unbalanced shards (>2 min variance)

• Adjust shard distribution if needed

• Set up alerts for regressions

Common Issues

Shard imbalance (one shard takes 2x longer)

• Use manual distribution with --grep patterns

• Group heavy tests together, distribute across shards

Cache misses despite correct key

• Verify hashFiles glob patterns match actual files

• Check if lock file changes on every run (shouldn't happen)

Playwright install fails with cache hit

• Ensure system dependencies installed separately: playwright install-deps

Tests fail in CI but pass locally

• Check environment variables (CI=true may affect behavior)

• Verify mock setup works in parallel execution

• Increase timeouts for slow operations

Success Criteria

• CI execution time < 15 minutes total

• Cache hit rate > 85% for dependencies

• Shard execution time variance < 2 minutes

• Zero timeout failures from slow tests

References

For detailed examples and templates:

• GitHub Actions Caching: https://docs.github.com/en/actions/using-workflows/caching-dependencies-to-speed-up-workflows

• Playwright Sharding: https://playwright.dev/docs/test-sharding

• pnpm in CI: https://pnpm.io/continuous-integration