Legacy system migration
Your old system holds on, but it slows growth. We migrate legacy applications to modern technologies in phases, without stopping the business and with controlled risk.
Modernise without stopping the business
A big-bang total rewrite is the surest recipe for failure. We apply the Strangler Fig pattern: we wrap the legacy system and migrate functionality piece by piece, with both systems coexisting during the transition. This reduces risk, keeps the service running and delivers value in weeks, not years. On top of that, every phase delivers value on its own: you never depend on the whole project finishing before you see improvements.
Data and knowledge preserved
The real value of a legacy system is not just in the code: it lives in the data and in the business rules the organisation forgot existed. We characterise current behaviour with characterisation tests, migrate data with validation and verification, and document the business rules so nothing is lost in the transition. And we train your team on the new platform from the start, so the transition never depends on us forever.
How we run the migration
- Analysis and characterisation of the current system
- Phased migration using the Strangler Fig pattern
- Characterisation tests that lock in behaviour
- Data migration with validation and verification
- Controlled coexistence of the old and new systems
- Zero service interruption during transition
Legacy system migration without the drama
Many companies live with old applications nobody dares touch: obsolete technologies, a single person who understands them, no integration with current systems. We specialise in legacy modernisation: migrations from COBOL, Visual Basic, old PHP, desktop applications and systems without documentation. We turn that risk into a controlled, phased roadmap that never stops the business.
How we run the migration
A phased transition with both systems coexisting and risk under control at all times.
System characterisation
We document what the legacy system actually does today: business rules, integrations, data and users. We create characterisation tests that capture its current behaviour and become the safety net of the whole migration.
Target system design
We define the modern target architecture and the phased plan: which functionality migrates first, how both systems will connect and what infrastructure is needed. You decide with a complete map before moving a piece.
Phased migration (Strangler Fig)
We wrap the old system with the new one and migrate functionality piece by piece. Each phase is deployed, validated against the characterisation tests and monitored in production before moving to the next.
Controlled legacy shutdown
When the new system covers all functionality, we switch the old one off gradually: read-only first, fully retired later. Historical data stays archived and accessible whenever your business needs it.
Frequently asked questions about legacy migration
Is migrating a legacy system very risky?
It is if done as a total big-bang rewrite. That is why we migrate in phases with the Strangler Fig pattern: the old system keeps running throughout the transition, each phase is validated before continuing and you can stop at any point with value already delivered.
Will we have to stop the service during the migration?
No. Controlled coexistence of both systems is the heart of our method: users keep working normally while we migrate functionality behind the scenes. System switches happen in agreed windows with a planned rollback.
What if the legacy code has no documentation or tests?
That is the most common situation, not the exception. The characterisation phase exists precisely for that: we rebuild the system knowledge with tests that document its real behaviour and interviews with the people who know it.
What happens to the historical data?
It is migrated with double validation: automated dump plus verification of totals, consistency and quality samples. At the end, the old system is retired but its data stays archived and queryable for as long as your business requires.