Add daily email for 2025-01-20

Reproducible or repeatable

source/_daily_emails/2025-01-20.md

@@ -0,0 +1,29 @@
+---
+title: Reproducible or repeatable
+date: 2025-01-20
+permalink: daily/2025/01/20/reproducible
+tags:
+  - software-development
+  - nix
+  - linux
+  - php
+cta: ~
+snippet: |
+  Is your software environment reproducible or just repeatable?
+---
+
+[In yesterday's email][0], I showed how I've been using Nix and flake files to build reproducible and shareable development environments for Drupal applications.
+
+The reason it's reproducible is the `flake.lock` file.
+
+Similar to `composer.lock` or `package-lock.json`, it captures the exact versions of the packages installed from the nixpkgs repository.
+
+This file, along with `flake.nix`, can be committed alongside the application code and anyone with Nix installed can run `nix develop` to get a shell with the same packages and dependencies.
+
+This isn't the same as other solutions, where you add something like `FROM php:8.2` but, because there's no lockfile, there's no guarantee the same package versions will be installed so there could be mismatches that cause errors.
+
+With `flake.lock`, the environment isn't just repeatable - it's completely reproducible.
+
+Locally, in a CI pipeline or in production.
+
+[0]: {{site.url}}/daily/2025/01/19/minimum-viable-development-environment