skill-build-systems

name	skill-build-systems
description	Hermetic builds, dependency management, build caching, reproducible builds, cross-compilation, build optimization. Use when optimizing build speed, ensuring reproducibility, or designing build infrastructure.
version	1.0.0

Skill: Build Systems

Fast, reproducible, hermetic builds. No network calls. Same output every time.

Hermetic Builds

Requirements:

• ✓ All dependencies vendored (in repo or locked)
• ✓ No network calls during build
• ✓ Deterministic output (bit-for-bit same)
• ✓ Works offline

Example (Bazel):

bazel build //app:binary
→ uses //third_party/go/dependencies.bzl (locked)
→ no network needed
→ same binary every time

Reproducible Builds

# Build 1
$ bazel build //app --action_env=BUILD_TIME=0
$ sha256sum bazel-bin/app/binary
→ abc123...

# Build 2 (week later)
$ bazel build //app --action_env=BUILD_TIME=0
$ sha256sum bazel-bin/app/binary
→ abc123...  # Identical!

Caching Strategy

• Local cache: ~/.cache/bazel (fast)
• Shared cache: S3/GCS (team)
• CI cache: Previous builds (speed up)

Cache hit = skip recompilation

Dependency Locking

# dependencies.lock
requests:
  version: 2.28.0
  sha256: abc123...
  url: https://pypi.org/packages/...

urllib3:
  version: 1.26.0
  sha256: def456...

Freeze dependencies → reproducible

Build Optimization

• Parallelism: -j 8 (8 parallel builds)
• Incremental: Only rebuild changed files
• Caching: Reuse previous outputs
• Sandboxing: Isolation (prevents hidden dependencies)

Binary Optimization

# Strip debug symbols
$ strip -s app

# Compress
$ upx -9 app

# Size reduction: 50MB → 5MB

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Status: Ready for build work
Best for: Build optimization, hermetic builds, reproducibility