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philosophy

Why Nix

Understanding why Nix is essential for reproducible infrastructure

The Problem

Every developer has experienced dependency hell: “it works on my machine” followed by hours of debugging why it doesn’t work on CI, production, or a colleague’s laptop.

The root cause is that traditional package managers don’t capture the complete environment. They assume a shared global state—system libraries, environment variables, compiler versions— that varies between machines.

The Solution

Nix takes a different approach: every dependency is explicit and content-addressed.

/nix/store/abc123-openssl-3.1.0/
/nix/store/def456-openssl-1.1.1/

Two versions of OpenSSL coexist. Each package specifies exactly which one it needs. No conflicts. No “DLL hell”. No “but it worked yesterday”.

Why Not Docker?

Docker gives you isolated environments. Nix gives you composable ones.

With Docker, you copy entire filesystem layers. Want to change one dependency? Rebuild the layer. Want to share code between containers? Mount volumes and pray.

With Nix, you compose packages like functions. Change a dependency and only that package rebuilds. Share derivations between projects trivially. Inspect exactly what changed.

Docker is isolation. Nix is composition.

Why Not Traditional Package Managers?

apt, yum, brew—they all share a fatal flaw: global mutable state.

Terminal window
apt install libfoo-dev  # Which version? Who knows.
pip install numpy       # Hope it matches your CUDA version.

Nix makes the implicit explicit:

buildInputs = [
  pkgs.libfoo_2_3        # Exact version
  pkgs.python3Packages.numpy  # Built against this nixpkgs
];

The Weyl Stack

For GPU infrastructure, reproducibility isn’t optional. CUDA versions, cuDNN builds, TensorRT compatibility—one mismatch and inference fails silently or crashes spectacularly.

Nix lets us:

  1. Pin everything — Same CUDA 12.8 + cuDNN 9.x + TensorRT 10.x everywhere
  2. Compose overlays — Add our patches without forking nixpkgs
  3. Cross-compile — Build for Grace/Jetson from x86_64 workstations
  4. Rollback instantly — Previous generation is one symlink away

This is why Nix. Not because it’s trendy. Because the alternatives don’t work at scale.