When tasked with modernizing a 40-year-old manufacturing system written in APL, I faced both technical complexity and organizational challenges that shaped my understanding of successful software development. This article shares key lessons learned during a four-year journey of rewriting critical legacy code while keeping a $10M business running smoothly.

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Milan Jovanović

Rewriting a legacy system built over four decades with APL into a modern stack using .NET, PostgreSQL, and React posed significant technical and organizational challenges. The process involved understanding the deeply complex and integrated legacy system, managing product vs. engineering priorities, and ensuring zero downtime during the migration. Key strategies included modular monolith architecture, cloud-ready design, and robust CI/CD pipelines. Success depended not only on technical solutions but also on effective stakeholder management and knowledge transfer.

What Rewriting a 40-Year-Old Project Taught Me About Software Development

Software Architecture: Building for the Future

<p>Thanks for sharing that valuable story. It’s always hard to satisfy the business side of a project when you have a lot of work to do in the background and nothing can be shown to them. Had recently a similar situation where we modernized an existing .net application to be containerised and cloud ready. And of course the project lead asked always for a demo of the new system.</p>
