Start with capability mapping, not technology wishlists
Identify business capabilities, their data boundaries, and pain points. This exposes what to split first and what must remain coupled during transition.
Use strangler patterns with clear cut lines
Pull one capability at a time behind a stable contract. Route traffic progressively, compare outputs, and keep rollback paths available until confidence is proven.
- Define target API contracts before code extraction.
- Run contract tests in both old and new services.
- Instrument latency, error rate, and consistency before cutover.
Keep data migration reversible where possible
Data is usually the largest risk. Use dual writes only when tightly controlled, and prefer migration windows with verification scripts. Maintain a clear source-of-truth policy during each stage.
Modernization KPIs for leadership and engineering
Track deployment frequency, mean time to restore, escaped defects, and time spent on legacy maintenance. Tie these to customer-facing reliability indicators and incident rates.