Moving off legacy without stopping the business
You cannot switch off the system that runs the company and rebuild it over a weekend. The calmer way to modernise, one slice at a time.
Replacing software that still runs your business is genuinely frightening, and it should be. The system is brittle, nobody fully remembers how it works, and yet real operations depend on it every single day. The temptation is to do a big rewrite and flip a switch. That is also how most modernisations turn into disasters.
We never do it all at once. We move the system over one slice at a time while everything keeps running, until the day the old code is finally gone and almost nobody noticed the transition happening underneath them.
The strangler-fig approach
The idea borrows its name from a plant that grows around a tree until it can stand on its own. You build the new system around the edges of the old one, route a piece of traffic at a time to it, and prove each slice in production before moving the next.
It is slower than a dramatic rewrite on paper, and far faster in reality, because you are never betting the whole business on one cutover that has to go perfectly.
What you land on
Done well, you do not just escape the old system. You land on a platform your team is genuinely glad to build on, with the documentation and clarity to keep going without us. That is the difference between a migration and a rescue.
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