Legacy systems modernised without stopping the business

A big-bang migration replaces the entire legacy system in a single cutover. The appeal is simplicity: one go-live date, one clean break. The risk is that any failure affects the whole platform simultaneously, and rollback is often impossible without losing weeks of work.

Incremental modernisation moves one bounded piece of the system at a time. Each change is small enough to test thoroughly, and the legacy system continues to serve production traffic until the replacement is proven. The total elapsed time may be longer, but the risk at any single point is far lower — and your business keeps running throughout.

It depends on the size and condition of the system, the number of integration points, and how much of the work your internal team can absorb in parallel. A focused assessment and roadmap phase typically takes four to six weeks. Execution phases for a mid-sized monolith commonly run between six and eighteen months when delivered incrementally.

We scope every engagement after the assessment, so you receive a timeline grounded in your actual codebase rather than a generic estimate. The roadmap phase exists precisely to remove that uncertainty before you commit to a larger programme.

The strangler-fig pattern works by placing a routing layer in front of the legacy system. New requests are directed to the replacement service for specific features, while everything else continues to hit the legacy application as normal. The legacy system is not switched off — it is gradually surrounded and superseded.

As each new service proves itself in production, the routing rules shift more traffic to it. The old code path for that feature is retired only once the new path is stable. At no point does the entire system depend on an untested replacement, which means a failure in one new service affects only that feature, not the whole platform.

A full rebuild carries a predictable appeal: a clean codebase, no legacy constraints, and the chance to apply everything your team has learned. The practical problem is that rebuilds routinely take longer than forecast, and during that period you are maintaining the old system in parallel while paying to build the new one.

Modernisation preserves the business logic that already works — the rules, workflows, and integrations your organisation has refined over years. You pay to change the structural parts that are causing problems, not to recreate what is already correct. For most enterprise platforms, that is significantly cheaper and faster than a clean-sheet rebuild.

The right answer depends on the state of the existing codebase. Our assessment phase is designed to give you an honest comparison of both paths before you commit to either.

A bounded context is a clearly defined part of the business domain where a specific model applies and a specific team owns the rules. In a monolith, these contexts exist implicitly — they are tangled together in shared databases and shared code, which is why a change in one area breaks something in another.

Domain-driven design makes those boundaries explicit. Once you know where one context ends and another begins, you have a natural seam along which to extract a service. The extracted service owns its own data and communicates with the rest of the system through a defined interface rather than direct database access. This removes the coupling that makes monoliths fragile and gives each team a clear area of ownership.

We do not consider a modernisation engagement finished at the point of technical delivery. The final phase of our engagement model is Operate: we produce runbooks, document architectural decisions, and run structured knowledge-transfer sessions with your team.

For teams that need additional support beyond handover, we offer an ongoing platform operations layer. This covers monitoring, incident response, and continuous improvement work on the new platform. The goal is that your internal team inherits a system they understand and can evolve independently — not a dependency on us.