Integrating legacy systems with modern APIs: practical approaches
How to connect legacy systems (ERP, custom systems, spreadsheets) to modern APIs without rewriting everything — with patterns, trade-offs, and when to use each approach.
The real problem of legacy integration
Most mid-size companies have one or more of these scenarios: an ERP without a modern API, an internal system with accessible database but no service layer, or a manual process of exporting from one system and importing into another.
The solution is rarely to rewrite the legacy. Rewriting is expensive, risky, and slow. The solution is to build bridges.
Four integration patterns
1. Polling with transformation — Scheduled job that reads from the legacy, transforms, and pushes to the destination. Simple and resilient when minute-level latency is acceptable.
2. Webhook adapter — When the legacy supports notifications, an adapter listens and transforms into a modern event.
3. Database bridge — Direct read-only access to the legacy database with a REST API layer on top. Works when there's no API but the database is accessible.
4. File-based integration — Many ERPs export files to directories. A watcher processes, validates, and ingests. Classic but effective for moderate volumes.
If you have systems that need to communicate but don't, get in touch.