Nix

Reproducible NixOS configurations with flakes use pinned dependencies and lock files to guarantee identical builds across environments. Create a flake.nix file that declares your system configuration, run `nix flake update` to generate flake.lock, and commit both to version control. This ensures every rebuild produces the same result.

Modular Nix configurations use composable modules that separate concerns—hardware, software, services—into reusable files. Organize modules by function, document the intent and dependencies of each, and import them into a central flake.nix. This pattern eliminates drift and makes configurations easier to maintain and version control.

Declarative configuration drift is prevented by treating your entire system state as code in version control. Use flakes to pin all dependencies, apply configurations atomically with `nixos-rebuild`, and regularly rebuild to catch divergence. This ensures your actual system always matches your declared configuration.

Home-manager integrates with NixOS to manage user environments declaratively—dotfiles, packages, services—alongside system configuration. Add home-manager as a flake input, import its NixOS module, and define user configurations in home.nix. Both system and user state remain reproducible and version-controlled together.

Flakes lock all dependencies at evaluation time, which can make ad-hoc customizations harder. They require explicit input declarations and add complexity compared to simple nix expressions. Flakes also demand discipline around lock file management and aren't suitable for highly dynamic, frequently-changing environments.

Use `nix flake check` to validate your flake structure and `nixos-rebuild dry-build` to evaluate configurations without applying changes. These catch syntax errors, missing dependencies, and configuration conflicts early. For deeper inspection, use `nix repl` to test expressions interactively.