Social security (EU member state, government programme)
Rewriting a 30-year-old social-security platform
Recovering business rules from three-decade-old code and rebuilding them as a tested .NET 10 and Blazor system, with a database layer 5–10× faster on the operations I tuned.
- Role
- Full-stack engineer
- Team
- Team of six developers
- Period
- About 2.5–3 years of a six-year programme
Result: business rules that lived only in decades-old code were rebuilt as a structured codebase covered by automated tests, and the database operations I tuned ran 5–10× faster.
Context
A social-security platform for an EU member state, built about three decades ago in a 4GL (a fourth-generation language, common in older business systems), needed a complete rewrite and redesign. The programme was planned to run for six years. I was part of the six-developer team for about two and a half to three of them.
The challenge
The business rules lived only in the legacy code. The client had very few specialists able to hand the knowledge over ready-made, so the rules had to be recovered from the code itself, and the new system had to be shown to behave like the old one.
What I did
- Worked full-stack: front end in Blazor, back end in .NET 10 with EF Core and SQL, running on Azure services.
- Helped recover business rules from the legacy code and re-implement them in a new, structured codebase.
- Wrote automated tests alongside the implementation. Together with early testing by the client, they were how we checked that the new system matched the old behaviour.
- Reworked the database layer: tuned indexes and EF Core data access, making the optimised operations 5–10× faster.
What I learned
When the only specification is old code, tests are the specification. Early client testing and automated checks turned unwritten rules into something the whole team could verify.