Microsoft Azure - Strangler Fig Pattern
Microsoft Azure Architecture Center documentation for the Strangler Fig Pattern.
Summary
Step-by-step documentation of the Strangler Fig pattern showing how to incrementally migrate a legacy system using a façade/proxy. Includes a concrete database migration example with shadow writes and a detailed walkthrough of the four migration phases. Also includes Azure WAF pillar guidance.
Key Arguments
- Introduce a façade (proxy) early that initially routes all requests to legacy.
- Iteratively migrate features to the new system; the façade shifts routing accordingly.
- After full migration, decommission the legacy system; optionally retain the façade as an adapter.
- Critical considerations: concurrent data store access, façade becoming a bottleneck or SPOF, keeping façade routing in sync with actual migration state.
- Database migration example: shadow writes (new system writes to both DBs), validation via read comparison, then cutover to new DB as system of record.
Concepts Covered
- Strangler Fig Pattern — comprehensive primary coverage with step-by-step guidance
- Anti-Corruption Layer Pattern — mentioned as useful alongside the façade
- Microservices Architecture — typical target architecture
Quality Notes
High quality; official and current (updated 2025). More implementation-focused than Fowler’s original bliki entry. The database migration example is particularly valuable.