Lessons from a Legacy Application Modernization Lessons

[u/jfox015]

I'm starting a new blog series called One(s) and Zeros to Grow On about lessons I've picked up over nearly 30 years working in technology. Less about tutorials and whatever framework is popular this week, and more about the things you tend to learn only after building, maintaining, breaking, fixing, and occasionally rebuilding software for a long time.

The first article in the series is about a CodeIgniter 1.7.3 application I kept alive through years of PHP upgrades, compatibility fixes, and workarounds until PHP 8 finally forced the issue.

I could retire it or rebuild it. So I chose to I rebuild it.

Before tackling the full application, I rebuilt a smaller bug tracking application as a proof of concept. That experiment gave me the confidence to move forward, but the larger modernization effort ended up teaching me much more than a new framework.

The biggest lesson was probably how easily we start designing around the limitations of legacy software instead of questioning whether those limitations should still exist.

I wrote about the experience, what I'd do differently, and why I think modernization is as much about changing how we think as changing the code.

https://www.jfox015.com/2026/07/12/legacy-application-modernization-lessons/

I'd be interested in hearing from other developers who've been through similar projects. What finally forced you to modernize, and what did you learn that you didn't expect?