Application Modernization Using Strangler Fig Pattern: A Quick Guide

A fig that inspired a whole new approach to application modernization, Stangler Fig. The story goes like this. Martin Fowler, Chief Scientist of Thoughtworks, was visiting Australia in the year 2004. He was captivated by the beauty of strangler figs and how these figs survive on an existing tree, slowly killing the tree and replacing it in the process.

This survival strategy of strangler figs got Fowler to design the concept of how large legacy systems can be refactored by implementing a new system over them. This new system would gradually replace the original one, typically over a few years. That is how the Strangler Fig Pattern came into existence.

In this post, you will get to understand what the Strangler Fig Pattern is, some use cases related to it, and step-by-step implementation of it. But before that, we need to understand the term app modernization (or application modernization).


What is Application Modernization?

Also known by terms such as legacy application modernization or software modernization, app modernization is the process of updating an existing software application. The primary motto behind doing this is to improve the existing system and make it compatible with modern technological advancements. Since user expectations vary as well with time, such upgrades help to meet the standards.

App modernization may include various approaches such as system migration, refactoring, the addition of new features and functionalities, and re-platforming, depending on certain needs of the system. The aforementioned upgrades come with advantages such as compatibility with modern technology, improved performance and efficiency, enhanced security, increased user experience, and compliance with evolving regulations.


How to Modernize Legacy Applications Successfully?

Modernizing your app involves a series of transformative journeys that collectively pave the way for a comprehensive digital evolution. To successfully modernize your legacy system, here is a simple yet comprehensive set of ways to execute it.

Assess your current state:

Assess your company’s current state and goals, then analyze existing systems and workforce. Establish a clear understanding of business needs and application landscape for a smooth transformation.

Determine your plan of action:

Once you have a clear picture of your business needs and challenges, convert your understanding into an actionable plan. Slowly, move on from general improvements to target specific technical objectives that can be achieved through app modernization. This may include selecting suitable hyperscalers or cloud providers.

Outline a roadmap:

Create a phased roadmap for app modernization, ensuring value addition and at the same time the absence of operational disruptions. Leverage external expertise to plan process and dependency changes, as internal perspectives may lack clarity.

Adapt to the new app environment:

Integrate your new app setup with existing workflows and personnel, empowering them with new capabilities and responsibilities. Plan cultural shifts alongside technical updates to ensure seamless adoption and prevent potential disengagement.

Now, let us move on to the Strangler Fig Pattern and understand how this specific approach has largely aided application modernization.


What is the Strangler Fig Pattern?

Strangler Fig Pattern is a specific approach that is used to carry out app modernization strategies. It is a software design pattern used to modify and replace legacy systems that no longer serve the latest conditions. Similar to the way strangler figs slowly engulf a host tree absorbing all its goodness, this pattern gradually replaces parts of an existing system with its new and modernized versions.

Technically speaking, Strangler Fig Pattern creates a new structure of microservices that implements a single function and over time replaces a function of the legacy system or simply creates new functions. The benefits of using this pattern are to reduce risk, minimize downtime, faster development cycles, reduce costs, and easier rollbacks.

To quote Martin Fowler – ‘The most important reason to consider a strangler fig application over a cut-over rewrite is reduced risk. A strangler fig can give value steadily and the frequent releases allow you to monitor its progress more carefully.’


Step-by-step Guide on Implementation of Strangler Fig Pattern

Here is a step-by-step guide for you to implement the Strangler Fig Pattern. By following these steps, you can successfully implement this pattern for the application modernization of your existing legacy system.

1. Evaluate your existing legacy system

Do not jump immediately into modernizing your existing application. First, you must analyze your application, and understand the underlying architecture and functionalities involved before starting the modernization process.

Identifying factors such as parts that are causing performance bottlenecks, parts that are essential to the business, and parts that are unnecessary, is crucial before you start modernizing your software.

2. Develop a strategic plan

Once the analysis is done and you are fully aware of your existing system, you can move forward to create a roadmap that strategizes the modernization process.

The plan should pinpoint the components that must be modernized on high priority, proceeding to the ones having lower priorities. This must come in a sequential order so that the process can be carried out seamlessly.

3. Develop a new architecture

Now that you have constructed a roadmap, follow it, and develop a new architecture for your system. The new architecture will replace the existing one. It should be a modular and scalable architecture that must be able to accommodate future technological advancements.

4. Lay the foundation with new components

Based on the new architecture you have developed your next step is to build the new components that are supposed to replace the existing ones. Ensure that the components are designed such that they seamlessly integrate with the existing application, fostering a smooth transition all the while maintaining functionality.

5. Test the new components

It is essential to test the newly developed components to ensure that they are working as per the requirements. Also, carry out the testing in a test environment. This will help you to detect any issues and resolve them before these new components are deployed into your system.

6. Replace the existing components

All tested and ready for deployment, it is time for the new components to start replacing the new ones. Follow the roadmap you have designed and implement the components accordingly.

7. Concluding the legacy system

Implement a phased approach while terminating the existing application alongside the deployment of new components. This is to ensure that no essential functionality is corrupted and there is minimum business disruption while the app modernization process is carried out.

8. Repeat

According to the Strangler Fig approach, successful migration will take place only when you keep repeating the entire process. So, keep developing new components, implementing them, and retiring the existing system.


Challenges Associated with Strangler Fig Pattern

It is important to keep in mind that there may be challenges and risks associated with the modernization process. Let us discuss these challenges in this section.

Increased system complexity:

Complexity management can be difficult while integrating the existing system with new, modernized components. Introducing new components often increases the complexity of the overall system which demands additional efforts for monitoring and maintenance. Thus, you must ensure careful planning and expertise to avoid such situations.

Transition risks:

Certain risks are associated with such transitions. They may include factors such as performance degradation, data migration issues, and regression risk. Temporary performance issues like system slowdowns or instability may arise while the integration is being carried out.

Again, data migration is a complex process prone to errors and thus may thorough planning and testing. Further, unintentional bugs or regressions might get introduced requiring careful testing and rollback strategies.

Testing and monitoring effects:

The modernization process comes with continuous and close monitoring of the performance and stability of both the new and existing systems. Also, you may find an increased need for extensive testing to ensure a seamless transition.

Organizational challenges:

The Strangler Fig Pattern approach requires effective change management strategies as this involves significant changes to the system. You may also find skill gaps which might be addressed by training and upskilling your development team.


For highly complex or tightly coupled legacy systems, the Strangler Fig Pattern approach might not be a recommendation. To ensure that it suits the existing system, you must carefully evaluate and determine whether the pattern aligns with your existing system.

Cost implications:

While, in most cases, it is a cost-effective approach, it might not be for all situations. In certain cases, the development, testing, and ongoing maintenance costs can be quite high.


Use Cases of Strangler Fig Pattern

The application of the Strangler Fig Pattern might be a fit when you:

  • are seeking a smooth and gradual transition, and considering migration one component at a time.
  • do not want a “big bang” approach as you are aware of the risks associated with it and want to explore a phased migration strategy.
  • are encountering pressing business needs for some new features but cannot afford a complete transformation, you might find a phased migration approach to be the perfect fit.
  • want the end users to be minimally impacted throughout the transformation process.

Many companies have adopted the Strangler Fig Pattern approach and successfully carried out their legacy application modernization. Leading brand names such as Amazon and Commonwealth Bank of Australia are few among them.

Amazon used it to modernize its retail platform and Commonwealth Bank of Australia used it to modernize its core banking platform.


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