itsual Strangler Fig Pattern
Overview
Named after the strangler fig tree, this pattern grows a new system around the old one and eventually replaces it, avoiding a big-bang rewrite.
When to Use
- Replacing a legacy monolith or major subsystem
- Risk of a full rewrite is unacceptable
- You can intercept calls to the old system (facade, proxy, routing layer)
Core Approach
- Identify a seam or entry point where you can intercept traffic
- Route selected functionality to the new implementation
- Incrementally migrate more behavior
- Keep the old system working for remaining paths
- Eventually remove the old system when traffic is fully migrated
Principles
- Prefer incremental value delivery over a long rewrite project
- Make the routing / facade explicit and observable
- Continuously reduce the surface area of the legacy system
Verification
- Migration progress is measurable
- Both old and new paths are correctly routed and tested
- Legacy system can be retired with confidence when ready