The big-bang rewrite is a myth. The idea that you can freeze the existing system, rebuild it from scratch, and switch over cleanly is almost always wrong. Requirements change during the rewrite. The existing system continues to accumulate edge cases that nobody documented. The cutover date slips. Eventually the rewrite project is cancelled, or the new system goes live with missing functionality that took years to rediscover. Key Brains does not do big-bang rewrites. We do phased modernisation — incremental, reversible, and conducted while the business continues to operate.
Every modernisation engagement begins with an honest assessment. We read the code. We run the tests — if there are any. We document the architecture, the dependencies, the data model, and the business logic that exists only in the application and nowhere else. We then produce a prioritised modernisation roadmap with clear milestones, measurable outcomes, and honest estimates. We tell you what we find, including the parts that are worse than expected.
Our primary modernisation strategy is the strangler fig — gradually replacing parts of the legacy system with modern components, routing traffic to the new components as they are completed, and eventually retiring the legacy system when it has been fully replaced. This approach means the legacy system remains live throughout. Users never experience a cutover. The business never stops.
Before we refactor anything, we add characterisation tests — tests that document the current behaviour of the code, including the bugs. This gives us a safety net. When we refactor, the characterisation tests tell us if we accidentally changed behaviour. Once the code is under test, we can begin improving it with confidence.
Legacy databases are frequently the hardest part of a modernisation project — tables with hundreds of columns, no foreign keys, names that made sense to someone in 2003, and business logic encoded in stored procedures. We migrate databases incrementally — dual-write strategies, shadow tables, and gradual cutover — without taking the system offline.
We modernise the technology stack alongside the architecture — moving from PHP 5 to PHP 8, from .NET Framework to .NET 8, from jQuery to React, from bare-metal servers to containerised deployments. We do this incrementally, one component at a time, not as a single large change.
A modernised system is only valuable if the team can maintain and extend it. We document architectural decisions, run knowledge transfer sessions with your engineering team, and leave codebases with README files that a new engineer can follow on their first day. We measure success by whether your team can operate the system without us.
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