[{"_1":2,"_3":-5,"_4":-5},"loaderData",{"_5":6},"actionData","errors","routes/blog-tag",{"_7":8,"_9":10},"tag",{"_31":82,"_72":83,"_35":84},"articles",{"_11":12,"_13":14,"_15":16,"_17":16,"_18":19,"_20":21,"_22":23,"_24":23,"_25":16,"_26":27},"content",[30],"pageable",{"_28":21,"_29":19},"totalElements",1,"totalPages","size",10,"number",0,"first",true,"last","numberOfElements","empty",false,"page_number","page_size",{"_31":32,"_33":34,"_35":36,"_37":38,"_11":39,"_40":-5,"_41":23,"_42":27,"_43":44,"_45":46,"_47":48,"_49":50,"_51":52,"_53":52,"_54":55,"_56":57,"_58":59,"_60":52,"_61":16,"_62":63,"_64":65,"_66":67,"_68":69,"_70":71},"id",23,"title","Strangler Fig Pattern","slug","clean-code-part-22-strangler-fig","excerpt","Gradually replace legacy system functionality with new implementations using the Strangler Fig pattern while keeping the system running.","# Advanced Clean Code Patterns Part 22: Strangler Fig Pattern\n\nThe Strangler Fig pattern enables gradual migration from legacy systems to new implementations. Named after the strangler fig tree that grows around its host, this pattern lets you incrementally replace functionality while keeping the system running.\n\n## 📋 At a Glance\n\n| Aspect | Details |\n|--------|---------|\n| Origin | Martin Fowler, 2004 |\n| Use Case | Migrating from legacy to modern systems |\n| Key Benefit | Continuous operation during migration |\n| Risk Level | Low (incremental changes) |\n\n---\n\n## 🎯 What You'll Learn\n\n- **Strangler Fig pattern** implementation\n- **Feature toggles** for gradual rollout\n- **Request routing** strategies\n- **Data synchronization** during migration\n- **Rollback strategies** when things go wrong\n\n---\n\n## Production Story: The Monolith Migration\n\nA company needed to migrate from a legacy Java 6 monolith to microservices:\n\n**Risky approach (rejected):**\n```text\n❌ Big Bang Rewrite\n- Stop development for 18 months\n- Rewrite everything\n- \"Flag day\" cutover\n- Result: Usually fails or exceeds timeline by 3x\n```\n\n**Strangler Fig approach:**\n```text\n✅ Incremental Migration\nWeek 1: Add proxy layer\nWeek 2: Route /api/users to new service (10% traffic)\nWeek 4: Route 100% of /api/users traffic\nWeek 6: Route /api/orders to new service\n...\nMonth 12: Legacy system decommissioned\n```\n\n---\n\n## Mental Model: Strangler Fig\n\n```text\n┌─────────────────────────────────────────────────────────────────┐\n│ STRANGLER FIG PATTERN │\n├─────────────────────────────────────────────────────────────────┤\n│ │\n│ PHASE 1: Add Facade │\n│ ┌────────────────────────────────────────────────────────────┐ │\n│ │ │ │\n│ │ Client ──→ [Proxy/Facade] ──→ Legacy System │ │\n│ │ │ │\n│ │ • All traffic through proxy │ │\n│ │ • Proxy just forwards requests │ │\n│ │ • Baseline established │ │\n│ └────────────────────────────────────────────────────────────┘ │\n│ │\n│ PHASE 2: Build & Route │\n│ ┌────────────────────────────────────────────────────────────┐ │\n│ │ │ │\n│ │ Client ──→ [Proxy/Facade] ──┬──→ New Service (Feature A) │ │\n│ │ └──→ Legacy (everything else)│ │\n│ │ │ │\n│ │ • New code handles some features │ │\n│ │ • Legacy handles the rest │ │\n│ └────────────────────────────────────────────────────────────┘ │\n│ │\n│ PHASE 3: Complete Migration │\n│ ┌────────────────────────────────────────────────────────────┐ │\n│ │ │ │\n│ │ Client ──→ [Proxy/Facade] ──→ New Services (everything) │ │\n│ │ │ │\n│ │ Legacy System ← (decommissioned) │ │\n│ │ │ │\n│ └────────────────────────────────────────────────────────────┘ │\n│ │\n└─────────────────────────────────────────────────────────────────┘\n```\n\n---\n\n## 🔬 Deep Dive\n\n### Pattern 1: Proxy-Based Strangler\n\n```java\n// Proxy that routes to new or legacy based on feature\n@RestController\n@RequestMapping(\"/api\")\npublic class StranglerProxy {\n\n private final FeatureToggleService featureToggles;\n private final LegacyClient legacyClient;\n private final NewUserService newUserService;\n private final NewOrderService newOrderService;\n\n // Users endpoint - migrated to new service\n @RequestMapping(\"/users/**\")\n public ResponseEntity