A legacy system is not just old. It is software the business depends on, that is hard to change safely. The goal of modernisation is to make change safe again.
Understand before replacing
Start by documenting what the system actually does, including the behaviour no one remembers asking for. Replacing it without that knowledge reproduces some behaviour and breaks the rest.
Replace in slices
A full rewrite delivers value only at the end, after a long period of risk. An incremental approach moves one capability at a time to the new system, with the old one running alongside.
- Pick a slice with clear boundaries and real value
- Build it in the new system and run it in parallel
- Migrate data with checks, then switch over
- Retire that part of the old system and repeat
Protect the data
Data outlives software. Plan migration as its own piece of work: clean it, rehearse the move, and reconcile the result before relying on it.
This topic is part of our IT Consulting & Technology Solutions work.