A sanitized write-up of an e-commerce platform upgrade I led as the sole developer for a manufacturing and e-commerce company. Company names, product details, and proprietary code are omitted. It describes the approach and engineering decisions only.
The online store ran on a years-old release of OpenCart, two major versions behind current, with no supported upgrade path. Custom modules and theme changes had accumulated on top of the core over several years, no documentation existed, and the original developers had left, so the behavior of much of the custom functionality was effectively undocumented.
As the sole developer, I led the upgrade from 1.5.6.4 to 3.0.3.8, covering 2,000+ products and 70,000+ historical orders, with zero data loss and no business interruption. With no documentation and no reliable automated path across that version gap, the project combined reverse engineering, data migration, and the rebuilding of custom functionality in roughly equal measure.
The two versions differ in database schema, templating, and module systems, so a direct in-place upgrade was not viable. I approached it as a rebuild on the new version paired with a controlled data migration, developed and rehearsed on a staging copy before any production cutover.
The store carried years of undocumented customization, and the original developers were no longer available. I read the legacy controllers, models, and template overrides to reconstruct what each feature actually did before deciding how to rebuild it. This ensured that behavior the business depended on was not inadvertently lost.
For each legacy module I made an explicit decision: adopt a maintained extension where a reliable one existed, or build a custom one where it did not. In both cases the changes were applied through the platform's modification system rather than by editing core files, so customizations sit on top of the core and the store remains upgradeable rather than being locked to a single version again.
The two schemas differ in table layout and relationships, so I wrote SQL scripts to clean, map, and rebuild the data rather than relying on an automated importer. Relational data such as product accessories, SEO URLs, and zone-to-geo-zone mappings had to be remapped table by table to fit the new structure.
The entire migration was built and rehearsed on a staging copy of the live store. I reconciled migrated record counts and spot-checked data against the source before switching over, so the production cutover was completed with zero data loss and no business downtime.
The storefront theme was rebuilt on the new template engine, with mobile responsiveness improved in the process. On the admin side, customizations and third-party module compatibility were re-implemented and resolved so the team's daily workflows continued without interruption.