Day 4 - Speed Up CI with Caching

Description

Your GitHub Actions workflow runs every time, but it's downloading and installing the same dependencies repeatedly. Each run takes 5+ minutes when it could take less than 2 minutes with proper caching.

Task

Add caching for dependencies to your GitHub Actions workflow.

Goal: Achieve 40% faster run times through intelligent caching.

Target

Time Reduction: 40% or more
Cache Hit Rate: 80%+ on subsequent runs
Cache Size: Reasonable (under 500MB)

Sample App

Slow Workflow (Before)

name: Slow CI

on: [push, pull_request]

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

      - name: Setup Node.js
        uses: actions/setup-node@v4
        with:
          node-version: '20.x'

      # No caching - downloads every time!
      - name: Install dependencies
        run: npm install

      - name: Run tests
        run: npm test

      - name: Build
        run: npm run build

View Solution

Solution

Optimized Workflow (After)

name: Fast CI

on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest

    steps:
      - uses: actions/checkout@v4

      - name: Setup Node.js
        uses: actions/setup-node@v4
        with:
          node-version: '20.x'
          cache: 'npm'  # Built-in npm caching

      - name: Cache node modules
        uses: actions/cache@v3
        with:
          path: |
            ~/.npm
            node_modules
          key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}
          restore-keys: |
            ${{ runner.os }}-node-

      - name: Install dependencies
        run: npm ci  # Faster than npm install

      - name: Cache build output
        uses: actions/cache@v3
        with:
          path: |
            dist
            .next
          key: ${{ runner.os }}-build-${{ hashFiles('src/**') }}
          restore-keys: |
            ${{ runner.os }}-build-

      - name: Run tests
        run: npm test

      - name: Build
        run: npm run build

Explanation

Cache Strategy

1. Package Manager Cache

- uses: actions/setup-node@v4
  with:
    cache: 'npm'

Benefits:

Caches global npm cache directory
Automatic invalidation on package-lock.json changes
Zero configuration

2. Node Modules Cache

- uses: actions/cache@v3
  with:
    path: node_modules
    key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}

Key Components:

path: What to cache
key: Unique identifier (OS + lockfile hash)
restore-keys: Fallback if exact key doesn't match

3. Build Output Cache

- uses: actions/cache@v3
  with:
    path: dist
    key: ${{ runner.os }}-build-${{ hashFiles('src/**') }}

Caches compiled output based on source code hash.

Cache Key Strategy

Exact Match Key

key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}

Creates keys like:

Linux-node-a1b2c3d4e5f6...
Changes when dependencies change

Restore Keys (Fallbacks)

restore-keys: |
  ${{ runner.os }}-node-

If exact key not found:

Try most recent cache starting with Linux-node-
Partial cache better than no cache

Performance Comparison

Scenario	Before	After	Improvement
Cold cache	5m 30s	5m 00s	9%
Warm cache (no changes)	5m 30s	1m 45s	68%
Dependency change	5m 30s	4m 30s	18%

Try to solve the challenge yourself first!

Click "Reveal Solution" when you're ready to see the answer.

Result

You should see:

✅ 40%+ faster average build times
✅ Cache hits on most runs
✅ Reduced GitHub Actions minutes usage
✅ Faster developer feedback

Workflow Log Output

Cache hit for key: Linux-node-a1b2c3d4e5f6
Restored cache from: /home/runner/.npm
Cache restored successfully
Total time: 1m 47s (previously 5m 32s)

Validation

Monitor Cache Performance

Add cache statistics step:

- name: Cache stats
  run: |
    echo "Cache key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}"
    du -sh ~/.npm 2>/dev/null || echo "No cache"
    du -sh node_modules 2>/dev/null || echo "No node_modules"

Compare Run Times

# View recent workflow runs
gh run list --workflow=ci.yml --limit 10

# Compare timing
gh run view <run-id> --log | grep "Total time"

Advanced Caching Patterns

Multi-Stage Caching

# Stage 1: Dependencies
- uses: actions/cache@v3
  id: cache-deps
  with:
    path: node_modules
    key: deps-${{ hashFiles('package-lock.json') }}

# Stage 2: Build (depends on source)
- uses: actions/cache@v3
  id: cache-build
  if: steps.cache-deps.outputs.cache-hit == 'true'
  with:
    path: dist
    key: build-${{ hashFiles('src/**') }}

# Only build if cache miss
- name: Build
  if: steps.cache-build.outputs.cache-hit != 'true'
  run: npm run build

Language-Specific Caching

Python (pip)

- uses: actions/setup-python@v4
  with:
    python-version: '3.11'
    cache: 'pip'

Go

- uses: actions/setup-go@v4
  with:
    go-version: '1.21'
    cache: true

Docker Layers

- uses: docker/build-push-action@v5
  with:
    cache-from: type=gha
    cache-to: type=gha,mode=max

Cache Cleanup

- name: Clear old caches
  if: github.event_name == 'schedule'
  run: |
    gh cache delete --all --repo ${{ github.repository }}
  env:
    GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}

Best Practices

✅ Do's

Use specific cache keys: Include lockfile hashes
Set restore-keys: Fallback to partial matches
Cache immutable data: node_modules, build artifacts
Monitor cache size: Keep under 500MB when possible
Version your caches: Include version in key if needed

❌ Don'ts

Don't cache secrets: Never cache credentials
Don't cache .git: Checkout action handles this
Don't use generic keys: cache-v1 is too broad
Don't cache OS files: System-specific files
Don't ignore cache misses: Monitor and optimize