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Service
Replace the legacy system without stopping the business
The system nobody dares touch is usually the one the business depends on most. We do not propose a big-bang rewrite. We move it piece by piece, keeping both systems correct until the last piece lands.
Resultater
- No freeze on the business during migration
- Knowledge out of one person's head and into documentation
- Supportable technology with a hiring market
- Years of history migrated with the audit trail intact
Service
Hvor det bruges
Strangler migration
New modules take over routes one at a time behind the same front door.
Re-platform
Same logic, modern runtime, supported infrastructure.
Full rebuild
When the process itself has changed beyond what the old model can express.
Det leverer vi
- Legacy code and data archaeology
- Phased migration architecture
- Dual-run and reconciliation tooling
- Data migration with validation reports
- Cutover planning and rollback rehearsal
Who this is for
- Companies running a business-critical system nobody wants to touch
- Teams whose platform blocks integration, mobile access or compliance requirements
- Organisations facing an end-of-support date on a framework, database or operating system
When this is the wrong choice
- Systems that are simply disliked but work and integrate fine — a UI refresh may be all that is warranted
- Cases where an off-the-shelf product now covers the whole domain properly
Problems this solves
Change is too risky
No tests, no documentation, original authors gone. Every change is a gamble, so nothing changes and the backlog ossifies.
Unsupported dependencies
Out-of-support runtimes fail security review and eventually block insurance, certification or enterprise contracts.
No way in or out
Without APIs, the system cannot feed a portal, a mobile app or a reporting tool.
Architecture and integration
- Routing façade in front of old and new so traffic shifts gradually and can be reverted instantly.
- Data migrated in stages with reconciliation reports against source-of-truth totals.
- New API layer exposed early, so portals and integrations can start before the rewrite finishes.
- Feature parity tracked as a checklist derived from real usage logs, not from the old manual.
How delivery runs
- 01
Assessment
Code, data, dependencies and actual usage examined. Frequently a third of the modules have not been used in years and are simply retired.
- 02
Behaviour capture
We write characterisation tests around current behaviour first — including the quirks people rely on — so change can be verified.
- 03
Strangler migration
Functionality moves area by area behind a routing layer. The old system keeps running until each area is proven.
- 04
Decommission
The legacy system is retired only after a period where both produce matching results.
Realistic timeline
Weeks 1–4
Assessment, usage analysis, migration plan and priced roadmap.
Months 2–6
Incremental migration, area by area, with the business running throughout.
Final phase
Parallel verification, then decommission.
Build or buy
Buy something existing when
- A mature product now covers the whole domain and your process is not unusual
- The legacy system's logic is mostly standard accounting or inventory practice
Build custom when
- The system encodes rules specific to how you win business
- You need APIs, mobile access and reporting the product cannot provide
- Migration to a product would mean abandoning process advantages
What moves the price
Test coverage at the start
No tests means writing them before safely changing anything — real work that pays for itself immediately.
Data model divergence
Decades of schema patches need mapping and cleansing rules.
Integration surface
Each connected downstream system is another contract to preserve during migration.
Where projects go wrong
Big-bang rewrite
Multi-year rewrites with no interim value are the classic failure. Incremental migration delivers throughout.
Lost undocumented rules
The quirks are often the business logic. Characterisation tests capture them before they are removed by accident.
Running two systems forever
Without a decommission date and owner, the legacy system survives and doubles the maintenance bill.
Vejledende budget
Data quality in the old system is the single biggest variable.
FAQ
Typiske spørgsmål
Can we keep using the old system during the project?+
Yes — that is the point of phasing. Both systems stay correct until the final module moves.
What if nobody understands the old code?+
Common. We reconstruct behaviour from the database, the logs and the people who use it daily.
You already have the idea. Let's define what comes next.
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