Introduction
Migrating from legacy systems to modern systems is no doubt a daunting task, this can be due to the risks of disruption, long project timelines, and potential failures. However one practical and risk-averse solution engineering teams can adopt to help with such risk is the Strangler Fig Pattern. Drawing inspiration from a naturally existing strangler fig tree, this pattern allows for a gradual and specific replacement of old systems with minimal disruption.
What is the Strangler Fig Tree Pattern?
A strangler fig tree is a tropical plant that begins its life by latching on to the body of an already existing tree (Host Tree) and overtime grows around such tree until it eventually replaces the host. This pattern perfectly encapsulates the phased approach at which old software systems are ported to modern software systems.
How does the strangler fig pattern work?
The pattern’s success lies in its methodical approach to system migration. Rather than attempting a risky "big bang" replacement, the strangler fig pattern encourages that systems are gradually migrated piece by piece. Here is a detailed look at how this works:
Incremental Migration: The key concept behind this pattern is incremental change. Rather than trying to rewrite entire systems all at once-a daunting and risky task-organisations move parts of the system step by step. This phased approach simplifies the process, allowing the engineering team to tackle each part one at a time.
Coexistence of the systems: During the migration, the legacy systems and the new systems run side by side. This allows the system to maintain uninterrupted service while the new components are tested and refined in real-time. By having both systems coexist, there is reduced pressure on how soon the migration should be completed, allowing for better-quality development and iterative improvements.
Phased Replacement: The migration is done in phases, where traffic is gradually shifted from the old system to the new system in a green/blue deployment strategy as new features or improvements are implemented. Over time, these new components take on more responsibility, reducing the reliance on the legacy system.
Minimal Disruption: A gradual transition means that users and stakeholders experience minimal disruption. Changes can be rolled out, tested, and refined, all while business operations continue smoothly.
Continuous Delivery: The Strangler Fig Pattern aligns well with continuous delivery principles, enabling frequent, small updates. This provides faster feedback cycles, allowing teams to adapt and improve with each phase.
Implementation Strategy
The diagram below illustrates the methodical steps to which the strangler fig pattern can be implemented:
Create a facade layer: Develop a new application layer or interface that can intercept and redirect requests between the legacy system and new modules. This layer acts as a gateway and allows you to control traffic flow.
Develop New Features: Begin implementing new functionality or improved versions of existing features within the modernised application.
Route Traffic Gradually: Slowly shift user traffic to the new components while monitoring performance and functionality. This step is crucial for identifying issues early and making necessary adjustments without impacting the entire system.
Decommission Legacy Components: As more features are migrated, progressively disable and remove unused parts of the legacy system, reducing its footprint until it can be entirely retired.
Ensure Consistent Testing and Monitoring: Continuous testing and monitoring throughout this process ensure that the migration is smooth, performance metrics are met, and any issues are addressed immediately.
Advantages of the Strangler Fig Pattern
Reduced Risk: Unlike a complete system overhaul, incremental changes reduce the risk of failure.
Flexibility: Teams can prioritize specific features or modules for migration based on business needs.
Better Adaptability: Each phase allows for learning and adjustments along the way.
Reduced Downtime: Users typically don’t experience service disruptions, making this approach perfect for mission-critical applications.
Conclusion
The Strangler Fig Pattern offers a strategic approach to modernizing legacy systems by enabling new architectures to take root and thrive alongside existing structures. Like the strangler fig tree slowly replacing its host, this pattern helps phase out outdated systems smoothly, creating a stronger and more sustainable software architecture. By embracing incremental change and phased development, businesses can steadily migrate to modern systems while maintaining stability and continuous improvement.
Top comments (0)