Nix

Skill: nix

What I do

I provide reproducible, declarative package management and build systems. Every build is deterministic, isolated, and pinned to exact versions. I eliminate "works on my machine" problems by treating packages as immutable values built from pure functions.

When to use me

• Creating reproducible development environments across teams and CI.
• Managing complex dependency trees with potential version conflicts.
• Building hermetic, bit-reproducible artefacts and immutable containers.
• Pinning exact dependencies for long-term project stability.
• Running multiple versions of tools side-by-side without interference.

Core principles

1. Reproducibility - Same inputs always produce identical outputs, regardless of machine state.
2. Purity - Builds are hermetic; they cannot access the network or undeclared system state.
3. Declarative - Configuration is expressed as pure functions in the Nix language.
4. Immutability - Packages in /nix/store are never modified; upgrades create new versions.
5. Atomic Operations - Installations and upgrades succeed completely or leave the system unchanged.

Patterns & examples

Pattern: flake.nix for Go projects (Modern)

{
  description = "Go project flake";
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-23.11";
    flake-utils.url = "github:numtide/flake-utils";
  };
  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let pkgs = nixpkgs.legacyPackages.${system};
      in {
        packages.default = pkgs.buildGoModule {
          pname = "myapp";
          version = "0.1.0";
          src = ./.;
          vendorHash = "sha256-abc123..."; # Pin dependencies
        };
        devShells.default = pkgs.mkShell {
          buildInputs = with pkgs; [ go_1_21 gopls golangci-lint ];
          shellHook = "echo 'Go development environment loaded'";
        };
      });
}

Pattern: buildGoModule with testing

pkgs.buildGoModule {
  pname = "myapp";
  version = "1.0.0";
  src = ./.;
  vendorHash = "sha256-abc...";
  checkPhase = ''
    go test -v ./...
  '';
  installPhase = ''
    install -Dm755 $GOPATH/bin/myapp $out/bin/myapp
  '';
}

Pattern: Docker image from Nix

pkgs.dockerTools.buildImage {
  name = "myapp";
  tag = "latest";
  contents = [ self.packages.${system}.default ];
  config.Cmd = [ "/bin/myapp" ];
}

Anti-patterns

• ❌ Impure Builds - Accessing network/system state without declaring it in inputs.
• ❌ Imperative Usage - Using nix-env -i instead of declarative flake.nix or shell.nix.
• ❌ Hardcoded Paths - Using /usr/bin/ instead of ${pkgs.package}/bin/command.
• ❌ Missing Lockfiles - Not committing flake.lock, leading to non-deterministic builds.
• ❌ Mixing Package Managers - Using apt or brew alongside Nix for the same dependencies.

KB Reference

~/vaults/baphled/3. Resources/Knowledge Base/AI Development System/Skills/DevOps-Operations/Nix.md

Related skills

• infrastructure-as-code - Declarative patterns for system state.
• dependency-management - Pinning and updating software versions.
• docker - Creating minimal, reproducible container images.
• automation - Scripting reproducible workflows.