Rewrite or upgrade a legacy PHP system?

The word covers two different projects, and the difference decides the risk. A re-platform rebuilds the same system on new foundations: the screens may change, but the rules, the data and the outcomes must match the old one. A redesign also changes how the business works. A re-platform has an answer key, because you can compare against the old system. A redesign doesn’t, and that makes it a different kind of project to manage.

An upgrade keeps the code and changes what it runs on. Many systems need some mix of these, part by part.

Details are on the case studies for the store, the loyalty system and the cabinet manufacturer. Most of our work is delivered under NDA, so many projects cannot be named.

The two-month project isn’t evidence that re-platforms are quick. We wrote the original, so we didn’t have to learn what it did. Don’t plan another team’s work on that number.

The eight-month project wasn’t a redesign. Every workflow the engineering team relied on was preserved and compared with the old system. The scope also took in an audit of the old code and schema, a database migration validated at each step, and a replaced front end.

The store didn’t need a rewrite in one go. WooCommerce itself is maintained, so we brought PHP, plugins and theme up to date progressively inside the maintenance engagement, which suits a store that has to keep selling.

None of these decides the question alone. A system can also split: keep the data and core rules, and replace only the front end or the worst module.

• Read the old system first. On an old system, the code is often the only accurate record of the business rules, including the odd ones that exist for a reason.
• Decide how you will compare. Choose the workflows and totals that will be checked against the old system before you start, not at the end.
• Plan the data as its own project. See the MySQL migration checklist.
• Keep the old system safe meanwhile. It stays live for the whole project, and it still needs backups and care. A long rebuild doesn’t pause the security exposure.
• Resist adding features during the move. Every change to a rule removes your ability to compare with the old system. Move first, improve afterwards.

See the four routes off PHP 5.6 for how this plays out at the oldest end, or the cost guide for what we charge. If you would like us to look at your system, our modernisation service starts with reading the code and giving you a written recommendation.