Modernising a legacy system: when and how to start
How to tell it is time to modernise, and why a gradual transition beats a big rewrite.
An old system that has served for years is not a problem in itself. The problem starts when it stops being enough — because of speed, security, availability of developers, or the inability to add new features.
So the question is not "is it old?" but "is it holding us back?"
Signals it is time to act
Bugs multiply, changes take disproportionately long, developers cannot be found, or the system cannot do what the business needs. A warning sign is also fear of deploying any change.
Gradually, not one big rewrite
A full rewrite is tempting but expensive and risky. Better to modernise in parts: wrap the old functionality first, replace it piece by piece, and keep the system running throughout.
Where to start
Start where the impact is greatest and the risk smallest. Add tests and monitoring before touching the code, so you know you are not breaking anything.