The temptation in every enterprise modernisation programme is the rewrite. A new stack, a new team, a two-year roadmap, and the promise that this time it will be different. It is never different. The systems that fail in production are the ones that tried to ship the new world in a single big-bang release.
Strangler-fig, deliberately
The strangler-fig pattern works. Route traffic at the edge. Move one capability at a time. Run new and old in parallel until the old has zero callers, then delete. Every quarter, customers see measurable improvement.
Data is the hard part
Code is replaceable. Data is not. Plan dual-writes, change-data-capture, and reconciliation tooling before you write a line of the new system.
Working with a modernisation partner
Hire a custom software development company that has done strangler-fig before, not one that wants to learn on your dime. Ask for the runbook from their last modernisation. Ask what broke in production. The answers will tell you everything.