What is Strangler Pattern in Microservices? How to use it?

As organizations embrace the microservices architecture style, the need to modernize legacy systems and seamlessly transition to microservices becomes crucial. However, undertaking a complete system overhaul can be daunting and risky. This is where the Strangler Pattern comes into play. The Strangler Pattern offers a structured approach to incrementally transform monolithic applications into a more flexible and scalable microservices architecture. In the past, we have understood about  Database Per Microservices, CQRS, Event Sourcing, Backend for Frontend, and Circuit-breaker pattern and in this article, we will explore what the Strangler Pattern entails and how to effectively employ it to ensure a successful migration.

What is Strangler Pattern in Microservices? How to use it?

The Strangler Pattern, coined by Martin Fowler, draws inspiration from the behavior of certain vines that slowly grow around a host tree, eventually replacing it. Similarly, in software architecture, the Strangler Pattern allows for the gradual replacement of a monolithic application with microservices, ultimately "strangling" the monolith.

The key idea behind the Strangler Pattern is to introduce new functionalities and components in the form of microservices around the existing monolithic system. These microservices encapsulate specific features or domains of the application, providing clear boundaries and allowing for independent development and deployment.

Over time, as more microservices are added, they take over the responsibilities of the monolith, reducing its scope and complexity.

How to Use the Strangler Pattern in Microservices?

Here  are details about how to use the Strangler Pattern in a Microservices architecture:

Identify the Monolith's Boundaries

Start by identifying the different domains or modules within the monolithic application. Analyze the dependencies and interactions between these components to determine potential boundaries for extracting microservices. Look for areas that are self-contained and have well-defined interfaces.

Create a Gateway

To ensure a smooth transition and maintain compatibility with the existing system, create a gateway or facade that sits between the monolith and the newly introduced microservices. This gateway acts as a proxy, routing requests between the monolith and the microservices based on the intended functionality.

Choose the First Candidate

Select a specific functionality or module within the monolith that is suitable for extraction into a microservice. This initial candidate should ideally be relatively independent and have a limited impact on the rest of the system. Extract this functionality into a microservice while ensuring it can still communicate with the monolith through the gateway.

Incrementally Replace Functionality

Once the first microservice is in place, gradually redirect the appropriate requests from the monolith to the newly created microservice. This can be achieved by updating the routing rules in the gateway. The microservice can now handle the specific functionality, while the monolith continues to handle the rest.

Iteratively Introduce New Microservices

Continue identifying new areas within the monolith that can be extracted into microservices. Repeat the process of creating, routing, and gradually transitioning the functionality until the monolith's core responsibilities are significantly reduced. This iterative approach allows for continuous deployment and testing of new microservices without interrupting the overall system's functionality.

Monitor and Refine

Throughout the migration process, closely monitor the system's behavior and performance. Measure the impact of each microservice and gather feedback from users and stakeholders. This information will help refine the architecture, identify potential bottlenecks, and make informed decisions for future microservice development.

Benefits of the Strangler Pattern

The Strangler Pattern offers several benefits when transitioning from monolithic applications to microservices:

Reduced Risk: By incrementally replacing components, the Strangler Pattern minimizes the risks associated with a complete system rewrite. It allows for a step-by-step transformation while ensuring the existing functionality remains intact.

Enhanced Agility: Microservices enable independent development and deployment, fostering agility and scalability. The Strangler Pattern paves the way for a more flexible architecture that aligns with modern development practices.

Gradual Learning Curve: Developers and teams can gradually familiarize themselves with microservices principles and technologies without the need for a steep learning curve. The Strangler Pattern allows for the adoption of microservices in a controlled and manageable manner, reducing the impact on the development team.

Improved Maintainability: With a microservices architecture, each service focuses on a specific domain or functionality, making it easier to understand, maintain, and update. The Strangler Pattern facilitates the decomposition of a monolithic system into smaller, more manageable components, leading to improved maintainability over time.

Scalability and Resilience: Microservices enable horizontal scalability, allowing organizations to scale individual services based on demand. The Strangler Pattern facilitates the transition to a more scalable and resilient architecture, where services can be independently scaled to handle varying workloads.

Challenges and Considerations

While the Strangler Pattern offers many advantages, it is important to be aware of potential challenges and considerations:

Data Consistency: As the system transitions from a monolith to microservices, ensuring data consistency becomes crucial. Careful planning and synchronization mechanisms need to be put in place to maintain data integrity across different services.

Integration Complexity: With an increasing number of microservices, managing communication and integration between services can become complex. Adopting appropriate communication protocols, such as synchronous or asynchronous messaging, is essential to ensure seamless interactions.

Operational Overhead: Introducing microservices adds operational complexity, as each service requires separate deployment, monitoring, and management. Organizations should be prepared to invest in robust infrastructure and tooling to support the operation and monitoring of a distributed system.

Continuous Refactoring: The Strangler Pattern is an ongoing process that requires continuous refactoring and reevaluation. It is essential to regularly assess the system's architecture and identify areas that can benefit from further decomposition into microservices.

Conclusion

The Strangler Pattern provides a structured approach for organizations to transition from monolithic architectures to microservices incrementally. By leveraging the Strangler Pattern, organizations can reduce the risks associated with a complete system overhaul while benefiting from the flexibility, scalability, and maintainability offered by microservices.

Through careful identification of boundaries, gradual extraction of functionality into microservices, and the establishment of communication gateways, organizations can transform their legacy systems while maintaining the integrity and functionality of the existing monolith. The Strangler Pattern serves as a pathway to evolutionary architecture, enabling organizations to embrace microservices and drive innovation in a controlled and manageable manner.

As with any architectural approach, it is essential to consider the specific needs and context of the organization when applying the Strangler Pattern. By understanding its principles and tailoring them to suit the unique requirements of the system, organizations can successfully navigate the journey towards a more modular, scalable, and resilient microservices architecture.