Legacy System Modernization

Legacy systems become urgent for specific reasons: the platform is unsupported, the people who understand it are leaving, a security requirement cannot be met, or every change takes weeks because nobody trusts the code.

The trap is that these systems usually work. They encode years of business rules — including edge cases nobody remembers deciding. That accumulated correctness is exactly what makes replacement risky, and why rewrites so often go badly.

We avoid the full rewrite wherever possible. Rebuilding a working system from scratch means reproducing years of undocumented behaviour while the original keeps changing. The usual outcome is a long project that ends with a system doing less than the one it replaced.

We prefer strangling the system incrementally. Put a stable interface in front of the old system, move one capability at a time behind that interface, and route traffic across gradually. Each step is small, reversible and delivers value on its own.

We treat the old system as the specification. Its behaviour, including the parts that look wrong, usually reflects a real requirement. Before changing anything we establish what current behaviour actually is, so differences are decisions rather than accidents.