Legacy modernisation

Big-bang rewrites are expensive, slow and risky: the old system keeps changing while the new one is built, and the switch-over is a cliff edge. I prefer to modernise in place, replacing one piece at a time while the business keeps running.

How I approach it

• Make it safe to change: tests around the behaviour that matters, monitoring that shows what the system is really doing, and a delivery pipeline you can trust.
• Find the seams: the places where a part of the system can be separated, replaced and switched over on its own.
• Move one piece at a time: to new code, a new platform, the cloud or, sometimes, back out of it.
• Keep the data right: migrations planned and rehearsed, with a way back if something goes wrong.

Experience

• PASS Technology Group: led the migration of a legacy monolithic platform to a globally distributed microservices architecture on Azure, and built the complete CI/CD pipeline from scratch.
• Expana: stabilised and modernised legacy workloads on Azure, rebuilt core services in TypeScript and Node.js, and improved reliability, observability and deployment safety.
• An AI app-building platform: built a Rust agent for moving legacy applications onto the platform: deterministic extraction, a digest-sealed data bundle, import, and record-by-record verification, resumable from the last safe point.
• LeasePlan: built a framework to migrate an application from ASP.NET Web Forms to ASP.NET MVC inside a single running application, effectively eliminating downtime.
• Neilson Financial Services: worked on the rewrite of a desktop CRM application for the web, and cut the database calls needed to render a single page from more than 250 to fewer than ten.
• Charter UK: technical lead on the redevelopment of a police intelligence product from VB6 to ASP.NET.
• Baxter: upgraded IdentityServer to a supported version of .NET Core, resolving critical compatibility and security concerns.