Legacy modernisation
Replace the system without stopping the business.
In short
VenSoc replaces legacy systems incrementally rather than through a big-bang rewrite. The approach routes traffic through a facade, moves one capability at a time behind it, and keeps the old and new systems running in parallel until each slice is proven — so the business never depends on a single cutover date.
- Approach
- Strangler pattern, incremental cutover
- First deliverable
- Characterisation tests capturing current behaviour
- Common origins
- Legacy PHP, Access, VB6, unsupported frameworks
- Rollback
- Every slice independently reversible
What this includes
- Legacy system assessment
- Incremental replatforming
- Characterisation test development
- Database modernisation
- API facade development
Why do big-bang rewrites fail?
Big-bang rewrites fail because the specification for the old system does not exist. The requirements live in fifteen years of accumulated behaviour, undocumented edge cases and workarounds that individual staff know but have never written down. A rewrite from the documented requirements reproduces a system nobody actually uses.
The first artefact VenSoc produces on a modernisation engagement is therefore not a design. It is a characterisation test suite: automated tests that capture what the existing system currently does, including the behaviour that looks like a bug and turns out to be load-bearing for a downstream process.
With that suite in place, replacement becomes verifiable. Each slice of new implementation must reproduce captured behaviour before it takes traffic, and any divergence is a deliberate, recorded decision rather than a discovery made in production.
Common questions
- Our system has no documentation and the original developer left. Can you still work on it?
- Yes — that is the normal starting condition. The first phase is archaeology: establishing how the system is actually built, run and deployed, where the data lives, what the seams are, and which behaviours are load-bearing. The output is a written assessment of the current state and a costed, sliced replacement plan. It is deliberately structured so that you can take that plan elsewhere if you prefer.