Best Practices in Strangler Pattern to Refractor Legacy Systems
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Best Practices in Strangler Pattern to Refractor Legacy Systems

Software needs to be scaled as a business grows. However, as software grows in size and complexity, it becomes more complicated to scale and develop as the business grows. Ensuing legacy systems may be optimized for better performance using best practices for the strangler application.

Innovation, development, and reinvention are essential for a thriving business. Scaling and building existing software platforms is a key part of this. However, doing so is not easy on monolithic systems.

Here is a situation that inevitably transpires as a business scales up. The software system in production needs to be upgraded. However, adding new features to it is risky due to its monolithic architecture. Traditional systems are one big chunk of software. The data layer, logic layer, and user interface are all strongly coupled. This is the main reason why older monolithic systems are so hard to maintain, upgrade and improve.

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How to deal with a system that is just too risky to try and upgrade? There is a high risk of failure when trying to implement major changes in monolithic systems.

The best solution for this is to create a new solution that works just like the current system. When the new solution is developed to the point that it functions as intended without problems, it can replace the older system.

The advantage of such an approach is that it is gradual. Instead of fully replacing the existing system by the deadline, a new system can be developed to gradually replace the previous system. Thus new features will be implemented earlier as and when they are developed. With the former approach, new features cannot be made available before the deadline.

This approach, known as the Strangler application, finds its roots back in 2014 when it was first developed and explained by Andy Pols and Chris Stevenson.

The new approach requires breaking down a big application into smaller components. A solid plan and careful preparation are necessary for this approach to work. It allows for a smooth transition and uninterrupted production for the business.

While breaking down the monolithic code, development teams can do one of two things. They can extract blocks of code. Or they can rewrite it.

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Extracting Blocks of Code

This option of copying old code is frequently used. However, reusing bits of old code in this manner might bring some of the older bugs back into the new system.

This method is vulnerable to what is called the IKEA effect. New developers make use of old code, which really needs to be refactored or written. A big problem here is that tightly coupled code may find its way into the new software.

Rewrite Code

Rewriting old code might seem more time, effort, and resource-intensive than carrying forward the old code into the new system. However, the time taken to rewrite the code is worth it.

Rewriting old code means looking up the business problem yet again. The team can make changes to older assumptions that are the root cause of the problem. They can enhance business processes with a fresh approach that leverages better logic.

In short, rewriting old code afresh can undo several problems that may have been present in the previous monolithic system.

For example, in the retail sector, a block of code runs the billing process. This block of code is crucial for the business since it is used very frequently and is at the core of operations. Thus, it is a good candidate for rewriting.

By revisiting this code, the team can rethink and reinvent the process to future-proof it. For instance, they might develop a modern and versatile architecture. Or they can leverage a payment gateway that allows new types of payments to be made.

Best Practices for Breaking Down Monolithic Applications Using Strangler Pattern

Dividing monolithic code into smaller bits requires technical expertise and a fair degree of courage. Such a task is easier said than done. Monolithic applications often lack clear domain design. They also retain bugs due to historical reasons.

One way of breaking down monolithic applications is to model them with respect to capability. Development can provide more business value by prioritizing features for extraction using the Strangler application. When done the right way, not only does it create value, the risk is also mitigated.

Certain tactics and methods work well for moving capabilities towards the strangler application. They are as follows.

Event Tapping

This is also referred to as event interception. Under this strategy, for each capability or event-driven application, using the stream of events, you can begin to replace or build functions for such events. With this method, you can build a system side by side that provides higher safety when in production.

Asset Capture

Every application has to manage a group of business assets and objects. They can be product orders, historical records, user accounts, or other key resources. The strangler application will have the sole capability for managing all these assets with the asset capture method.

Due to its intuitive nature, this is an art rather than science. But with this tactic, you have a way of creating services characterized by clear-cut responsibilities and domain concepts.

Service Bubbles

You can view all applications as systems that require a group of APIs. The IT realm has now transitioned to the service-oriented approach for all phases of design and development. You can think of refactoring and breaking up old code using the service-centric paradigm.

This strategy looks at business capabilities present in the old application and uses them for making smaller strangler services where the logic for all capabilities are encapsulated in different independent bubbles.

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Conclusion for Best Practices in Strangler Pattern to Refractor Legacy Systems

With the best practices in strangler pattern to refractor legacy systems approach, the end result is a service mesh that supports all capabilities coming from the monolithic application. You can ultimately create microservice architecture by dividing up code units into independent services geared towards business capabilities. Using this approach, you can break down the old monolithic application by shifting each business capability towards independent services.

Further blogs within this Best Practices in Deploying the Strangler Pattern to Refractory Legacy Systems and Microservices Architecture Review Board category.