Strangling a legacy ERP without stopping operations
Incremental replacement of an unmaintainable ERP, one capability at a time, with both systems running in parallel throughout.
Client: Distribution company (anonymised)
- Planned downtime across the migration programme
- Zero
- Cutover, with rollback available at every step
- Incremental
- Data migration validated against legacy totals
- Reconciled
- Business rules that previously existed only in code
- Test-covered
A decade-old system still ran the business but could no longer be changed: the original vendor was gone, there were no tests, and a single schema change risked invoicing. Two previous rewrite attempts had been abandoned.
Rather than a rewrite, we placed an API facade in front of the legacy system and migrated capabilities behind it one at a time — starting with reporting, which carried no write risk, then procurement, then stock. Each migration shipped with a regression suite pinning existing behaviour and a per-route rollback. The legacy system stayed authoritative until the last consumer of each capability had moved.
Technologies used
- Node.js
- TypeScript
- PostgreSQL
- Kafka
- Docker
- Kubernetes
- Nginx
Services engaged
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