The Strangler Fig Pattern

Legacy mobile applications are notorious for their technical debt, monolithic structure, and sluggish adaptability to modern demands. Yet rewriting an entire app from scratch can be expensive and high-risk. Enter the Strangler Fig pattern—a strategic approach to modernizing applications incrementally while maintaining business continuity. This technique proved transformative for a global retailer tackling its aging mobile app through a modular

The Strangler Fig pattern focuses on gradually replacing legacy code by layering new functionalities around it, ensuring operations proceed without disruption. For the retailer in question, this meant embedding modernized components—one step at a time—while deprecating pieces of legacy code along the way. s.

The company leaned on modular micro-apps, each with its own Backend-For-Frontend (BFF). This encapsulated design had several advantages:  

- Faster feature delivery 🚀  

- Improved reusability ♻️  

- Simplified domain-specific development 🤝 


Additionally, the use of React Native played an integral role in bridging old and new worlds. Through bidirectional communication, React Native interfaced seamlessly with legacy infrastructure, allowing the company to modernize without compromising its core functionalities or user experience. 

Sensitive data—such as authentication credentials—was securely exchanged between the legacy ecosystem and new components. Trusted systems like the iOS Keychain handled this responsibility to protect user and business-critical data.

The implementation relied heavily on contract testing to safeguard the interactions between domain boundaries. Gradual feature rollouts within an experimentation framework allowed real-world testing of new functionalities with controlled risk. 

The process delivered measurable wins while sidestepping the pitfalls of full rewrites:  

- ⚡ Time-to-first-value was reduced to just 1 month, compared to 2 years for an all-at-once rebuild.  

- 📈 Median cycle times improved by 50%, enabling faster deployment of production-ready features.  

However, challenges remained. The added complexity of managing both new and old systems introduced scaling concerns. Resilience data over the long term is still under observation, and the approach demands detailed planning and collaboration across teams to align organizational goals.  

Is The Strangler Fig Right for You?  

Adopting the Strangler Fig pattern requires context-aware decision-making. For teams looking to modernize quickly without risking system downtime, this approach is a promising option. Yet it works best as part of a broader strategy that accounts for technical constraints, scalability, and resource availability.

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