---
id: patricio0312rev/skills/monorepo-ci-optimizer
version: "0dddf8b8"
license: MIT
install: manual
updated: 2026-01-12
---

# monorepo-ci-optimizer — This skill optimizes continuous integration workflows for monorepo architectures by detecting which packages and services have actually changed, then executing only the necessary builds and tests. It helps teams eliminate wasted compute cycles and ship faster by skipping redundant work across large codebases.

Publisher: patricio0312rev · Stars: 52 · Updated: 2026-01-12

Install (manual): `git clone https://github.com/patricio0312rev/skills`

## SKILL.md

# Monorepo CI Optimizer

Run only affected builds and tests in monorepos for faster CI.

## Affected Detection Strategy

### Using Turborepo

```yaml
# .github/workflows/ci.yml
name: CI

on:
  pull_request:
  push:
    branches: [main]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0 # Need full history for affected detection

      - uses: actions/setup-node@v4
        with:
          node-version: "20"
          cache: "pnpm"

      - run: pnpm install

      - name: Build affected
        run: |
          pnpm turbo run build --filter='...[origin/main]'

      - name: Test affected
        run: |
          pnpm turbo run test --filter='...[origin/main]'

      - name: Lint affected
        run: |
          pnpm turbo run lint --filter='...[origin/main]'
```

### Using Nx

```yaml
build:
  runs-on: ubuntu-latest
  steps:
    - uses: actions/checkout@v4
      with:
        fetch-depth: 0

    - uses: nrwl/nx-set-shas@v4

    - uses: actions/setup-node@v4
      with:
        node-version: "20"
        cache: "npm"

    - run: npm ci

    - name: Build affected projects
      run: npx nx affected:build --base=$NX_BASE --head=$NX_HEAD

    - name: Test affected projects
      run: npx nx affected:test --base=$NX_BASE --head=$NX_HEAD --parallel=3

    - name: Lint affected projects
      run: npx nx affected:lint --base=$NX_BASE --head=$NX_HEAD
```

## Remote Caching (Turborepo)

```yaml
- name: Setup Turborepo cache
  uses: actions/cache@v3
  with:
    path: .turbo
    key: ${{ runner.os }}-turbo-${{ github.sha }}
    restore-keys: |
      ${{ runner.os }}-turbo-

- name: Build with remote cache
  run: pnpm turbo run build
  env:
    TURBO_TOKEN: ${{ secrets.TURBO_TOKEN }}
    TURBO_TEAM: ${{ secrets.TURBO_TEAM }}
```

## Nx Cloud Integration

```yaml
- name: Setup Nx Cloud
  run: |
    npx nx-cloud start-ci-run --distribute-on="3 linux-medium-js"
  env:
    NX_CLOUD_ACCESS_TOKEN: ${{ secrets.NX_CLOUD_ACCESS_TOKEN }}

- name: Run affected
  run: |
    npx nx affected --target=build --parallel=3
    npx nx affected --target=test --parallel=3
    npx nx affected --target=lint --parallel=3
```

## Manual Affected Detection

```typescript
// scripts/get-affected.ts
import * as path from "path";
import { execSync } from "child_process";
import * as fs from "fs";

interface Package {
  name: string;
  path: string;
  dependencies: string[];
}

function getChangedFiles(base: string = "origin/main"): string[] {
  const output = execSync(`git diff --name-only ${base}...HEAD`, {
    encoding: "utf-8",
  });
  return output.split("\n").filter(Boolean);
}

function getPackages(): Package[] {
  const packagesDir = path.join(process.cwd(), "packages");
  return fs.readdirSync(packagesDir).map((name) => {
    const packageJson = JSON.parse(
      fs.readFileSync(path.join(packagesDir, name, "package.json"), "utf-8")
    );
    return {
      name: packageJson.name,
      path: `packages/${name}`,
      dependencies: [
        ...Object.keys(packageJson.dependencies || {}),
        ...Object.keys(packageJson.devDependencies || {}),
      ],
    };
  });
}

function getAffectedPackages(): string[] {
  const changedFiles = getChangedFiles();
  const packages = getPackages();
  const affected = new Set<string>();

  // Direct changes
  changedFiles.forEach((file) => {
    packages.forEach((pkg) => {
      if (file.startsWith(pkg.path)) {
        affected.add(pkg.name);
      }
    });
  });

  // Dependent packages
  let changed = true;
  while (changed) {
    changed = false;
    packages.forEach((pkg) => {
      if (!affected.has(pkg.name)) {
        const hasAffectedDep = pkg.dependencies.some((dep) =>
          affected.has(dep)
        );
        if (hasAffectedDep) {
          affected.add(pkg.name);
          changed = true;
        }
      }
    });
  }

  return Array.from(affected);
}

// Output for GitHub Actions
const affected = getAffectedPackages();
console.log(`::set-output name=packages::${affected.join(",")}`);
console.log(`Affected packages: ${affected.join(", ")}`);
```

## Matrix Strategy for Affected Packages

```yaml
detect-affected:
  runs-on: ubuntu-latest
  outputs:
    packages: ${{ steps.affected.outputs.packages }}
  steps:
    - uses: actions/checkout@v4
      with:
        fetch-depth: 0

    - id: affected
      run: |
        PACKAGES=$(node scripts/get-affected.ts)
        echo "packages=$PACKAGES" >> $GITHUB_OUTPUT

test-affected:
  needs: detect-affected
  if: needs.detect-affected.outputs.packages != ''
  runs-on: ubuntu-latest
  strategy:
    matrix:
      package: ${{ fromJSON(needs.detect-affected.outputs.packages) }}
  steps:
    - uses: actions/checkout@v4

    - uses: actions/setup-node@v4
      with:
        node-version: "20"
        cache: "pnpm"

    - run: pnpm install

    - name: Test ${{ matrix.package }}
      run: pnpm --filter ${{ matrix.package }} test
```

## Workspace-aware Caching

```yaml
- name: Cache workspace builds
  uses: actions/cache@v3
  with:
    path: |
      packages/*/dist
      packages/*/node_modules/.cache
    key: ${{ runner.os }}-workspace-${{ hashFiles('**/pnpm-lock.yaml') }}-${{ hashFiles('packages/**/*.ts') }}
    restore-keys: |
      ${{ runner.os }}-workspace-${{ hashFiles('**/pnpm-lock.yaml') }}-
      ${{ runner.os }}-workspace-
```

## Parallel Execution

```yaml
- name: Build all packages in parallel
  run: pnpm turbo run build --parallel

- name: Test with controlled parallelism
  run: pnpm turbo run test --concurrency=3
```

## Optimization Metrics

```markdown
## Before Optimization

- Full build: 25 minutes
- All tests: 15 minutes
- Total: 40 minutes
- Runs on every PR

## After Affected Detection

- Affected build: 5 minutes (80% reduction)
- Affected tests: 3 minutes (80% reduction)
- Total: 8 minutes (80% reduction)
- Only runs necessary checks

## With Remote Caching

- Cache hit build: 30 seconds (98% reduction)
- Cache hit tests: 1 minute (93% reduction)
- Total: 1.5 minutes (96% reduction)
```

## Best Practices

1. **Fetch full history**: `fetch-depth: 0` for accurate diffs
2. **Topological order**: Build dependencies first
3. **Remote caching**: Share cache across CI runs
4. **Parallel execution**: Run independent tasks concurrently
5. **Incremental builds**: Only rebuild what changed
6. **Dependency graph**: Track package relationships
7. **Force full build**: On main branch merges

## Output Checklist

- [ ] Affected detection implemented
- [ ] Turborepo or Nx configured
- [ ] Remote caching enabled
- [ ] Parallel execution optimized
- [ ] Matrix strategy for packages
- [ ] Workspace-aware caching
- [ ] Dependency graph documented
- [ ] Before/after metrics tracked


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