# Build Optimization

> Optimize CI build speed — Docker layer caching, dependency caching, multi-stage builds, parallelism, and build matrix strategies.

- **Type:** Skill
- **Install:** `agentstack add skill-sawrus-agent-guides-build-optimization`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [sawrus](https://agentstack.voostack.com/s/sawrus)
- **Installs:** 0
- **Category:** [Cloud & Infrastructure](https://agentstack.voostack.com/c/cloud-infrastructure)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [sawrus](https://github.com/sawrus)
- **Source:** https://github.com/sawrus/agent-guides/tree/main/areas/devops/ci-cd/skills/build-optimization
- **Website:** https://sawrus.github.io/agent-guides

## Install

```sh
agentstack add skill-sawrus-agent-guides-build-optimization
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# Skill: Build Optimization

> **Expertise:** Docker BuildKit cache mounts, GitHub Actions/GitLab CI caching, parallelization, selective test runs.

## When to load

When a pipeline takes > 5 minutes, Docker builds are slow, or you need to reduce CI costs.

## Docker Layer Cache Strategy

```dockerfile
# ✅ Order layers by change frequency (least → most)
FROM python:3.12-slim AS builder

# 1. System deps (changes rarely → cache long)
RUN apt-get update && apt-get install -y --no-install-recommends gcc libpq-dev

# 2. Python deps (changes on lockfile update → medium cache)
WORKDIR /app
COPY requirements.txt .
RUN pip install --user --no-cache-dir -r requirements.txt

# 3. App code (changes every commit → no cache benefit here)
COPY src/ ./src/
```

## BuildKit Cache Mounts (Docker 18.09+)

```dockerfile
# Cache pip downloads across builds (never invalidated by lockfile change)
RUN --mount=type=cache,target=/root/.cache/pip \
    pip install --user -r requirements.txt

# Cache npm across builds
RUN --mount=type=cache,target=/root/.npm \
    npm ci --cache /root/.npm

# Cache Go modules
RUN --mount=type=cache,target=/go/pkg/mod \
    go build ./...
```

## GitHub Actions Cache

```yaml
# Python: built-in setup-python cache
- uses: actions/setup-python@v5
  with:
    python-version: "3.12"
    cache: pip                      # hashes requirements*.txt automatically

# Node: built-in setup-node cache
- uses: actions/setup-node@v4
  with:
    node-version: "20"
    cache: npm

# Go: manual cache
- uses: actions/cache@v4
  with:
    path: |
      ~/.cache/go-build
      ~/go/pkg/mod
    key: go-${{ runner.os }}-${{ hashFiles('**/go.sum') }}
    restore-keys: go-${{ runner.os }}-

# Docker layer cache via GHA cache backend (BuildKit)
- uses: docker/build-push-action@v6
  with:
    cache-from: type=gha
    cache-to: type=gha,mode=max
```

## GitLab CI Cache

```yaml
# Global cache shared across jobs (same branch)
cache:
  key: ${CI_COMMIT_REF_SLUG}
  paths: [.cache/pip, node_modules/]

# Per-job cache with fallback
test:
  cache:
    key:
      files: [requirements.txt]     # invalidate only when lockfile changes
    paths: [.cache/pip]
    fallback_keys:
      - ${CI_COMMIT_REF_SLUG}-pip
      - pip
```

## Parallelization Strategies

```yaml
# GitHub Actions: parallel jobs
jobs:
  test-unit:
    runs-on: ubuntu-latest
    steps: [... run pytest tests/unit ...]

  test-integration:
    runs-on: ubuntu-latest
    steps: [... run pytest tests/integration ...]

  lint:
    runs-on: ubuntu-latest
    steps: [... ruff + mypy ...]

  # Only after all three pass:
  build:
    needs: [test-unit, test-integration, lint]
```

```yaml
# Matrix builds: test multiple versions in parallel
strategy:
  matrix:
    python-version: ["3.11", "3.12"]
    os: [ubuntu-latest, windows-latest]
  fail-fast: false    # don't cancel other matrix jobs on first failure
```

## Selective Test Runs (path filtering)

```yaml
# GitHub Actions: only run relevant tests based on changed files
jobs:
  changes:
    outputs:
      backend: ${{ steps.filter.outputs.backend }}
      frontend: ${{ steps.filter.outputs.frontend }}
    steps:
      - uses: dorny/paths-filter@v3
        id: filter
        with:
          filters: |
            backend: ['src/backend/**', 'requirements.txt']
            frontend: ['src/frontend/**', 'package.json']

  test-backend:
    needs: changes
    if: needs.changes.outputs.backend == 'true'
    steps: [... pytest src/backend ...]

  test-frontend:
    needs: changes
    if: needs.changes.outputs.frontend == 'true'
    steps: [... jest src/frontend ...]
```

## Build Time Benchmarks (targets)

| Stage | Good | Acceptable | Fix needed |
|:---|:---|:---|:---|
| Dependency install (cached) |  90s |
| Docker build (layer cache hit) |  3m |
| Unit tests |  5m |
| Full pipeline (PR) |  10m |

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [sawrus](https://github.com/sawrus)
- **Source:** [sawrus/agent-guides](https://github.com/sawrus/agent-guides)
- **License:** MIT
- **Homepage:** https://sawrus.github.io/agent-guides

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-sawrus-agent-guides-build-optimization
- Seller: https://agentstack.voostack.com/s/sawrus
- Browse the marketplace: https://agentstack.voostack.com/browse

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