Legacy System Modernization
Replacing a system without stopping the business that depends on it.
Legacy systems keep working until the people who understand them leave or a vendor stops supporting them. We modernise in stages, running the old and new systems side by side, so the business keeps operating while the replacement is proven.
Tools we work in
- COBOL
- .NET Framework
- PHP
- Java
- PostgreSQL
- Kafka
- Docker
- Terraform
Scope
What this covers
The specific work included when you engage us for this service.
- Assessment of the existing system, its dependencies and its undocumented behaviour
- Strangler-fig migration that replaces components one at a time
- Data migration with reconciliation between old and new stores
- Reimplementation on current frameworks and supported runtimes
- Interfaces that let old and new systems exchange data during the transition
- Phased decommissioning with a rollback path at each stage
- Documentation of behaviour that currently exists only in someone's head
What you receive
- 01A migration plan that sequences the work and names the risks
- 02A running modernised system with the old one still available during transition
- 03A decommissioning checklist and a record of what now runs where
Questions
Legacy System Modernization, answered
Can we just rewrite it all at once?
You can, and it is the most common way these projects fail: the rewrite takes longer than planned, the business keeps moving, and the old system has to be maintained in parallel until the new one catches up, at which point the new one is already behind. Incremental replacement is slower to start and considerably more likely to finish.
How do you deal with behaviour nobody documented?
We treat the running system as the specification. Real inputs and outputs are captured, a test suite is built against them, and the old system stays available to compare against. Parts of the code that exist only to work around an old bug are the usual surprises, and we surface them so you can decide whether to keep the behaviour or drop it.
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Tell us where the manual work is
A 30-minute call. We map the process, tell you what we would automate or build first, and what it costs. No retainer before you agree the scope.
- No retainer before scope is agreed
- Written plan you can act on alone
- Worldwide delivery, on your hours