20-year-old VB system modernized without a single hour of downtime.
A manufacturing company’s entire operation ran on a Visual Basic application from 2003. We migrated it to a modern stack while the business kept running. Zero downtime, zero data loss.
The short version.
A mid-size manufacturer had been running their entire production, inventory, and order management on a Visual Basic 6 application built in 2003. The system contained 20 years of accumulated business logic, custom workflows, and institutional knowledge that no one fully understood anymore.
After a structured engineering audit to document the existing system, we executed a phased custom software migration to a modern web-based platform using the strangler fig pattern, gradually replacing components while the old system continued running. Every piece of business logic was preserved, documented, and tested. The old system was decommissioned after 6 months of parallel operation with zero data discrepancies.
The system everyone depends on but no one can maintain.
The VB6 application was the backbone of the business. Every order, every production run, every shipment flowed through it. But after 20 years, it had become a critical liability:
- Single point of failure: ran on one physical server; any hardware failure would halt the entire operation
- No available developers: the original developer retired 8 years ago; VB6 expertise is nearly extinct
- Security vulnerabilities: Windows Server 2008, unpatched, running on the network with direct database access
- No remote access: desktop-only application; management couldn’t view reports outside the factory
- Reporting bottleneck: generating month-end reports took 4+ hours of manual Crystal Reports manipulation
- Undocumented business logic: 200K+ lines of VB6 with no documentation, no tests, and custom pricing rules buried in event handlers
A “big bang” rewrite was too risky. The business couldn’t afford any downtime, and no one was confident that all business logic could be captured upfront.
Strangler fig migration — module by module.
We used the strangler fig pattern: build new modules alongside the old system, gradually redirect traffic, and only decommission legacy components after the replacement is proven in production:
- Business logic extraction: systematic analysis of every VB6 form, module, and stored procedure; documented 340+ business rules
- Database migration: Access database → PostgreSQL with automated ETL pipeline and real-time sync during transition
- Module-by-module rebuild: started with reporting (lowest risk), then inventory, then orders, then production
- Parallel running: both systems operated simultaneously with automated data reconciliation checks every hour
- Real-time dashboards: replaced 4-hour Crystal Reports with instant web dashboards accessible from any device, hosted on cloud infrastructure
- Automated testing: 1,200+ integration tests validating every business rule against the legacy system’s outputs
Anti-corruption layer with dual-write consistency.
An anti-corruption layer sat between the old and new systems, translating data formats and maintaining consistency during the transition. Every write operation went to both systems, with automated reconciliation catching any discrepancies.
Strangler fig | 0 discrepancies over 6 months of parallel running
The reconciliation engine compared every data point between old and new systems hourly. Over 6 months of parallel running, we achieved 100% data consistency with zero discrepancies before decommissioning the legacy system.
“We were terrified of touching our VB system — it ran everything. Synthax migrated us piece by piece without a single minute of downtime. Our team didn’t even notice the switch. Now I can check reports from my phone.”
Managing Director, Mid-size manufacturer
Stuck on a legacy system
you can’t afford to break?
We’ll audit your current system and design a migration path with zero downtime.