The Monolith to Microservices Journey: A Case Study

Migrating a production system is like changing the engines on a plane while it’s flying. This case study details our 18-month journey of deconstructing a legacy monolith into a high-scale event-driven architecture.

The Challenge: The “Big Ball of Mud”

Our legacy system was a 10-year-old monolith.

• Deployment: One change required a full 45-minute deployment.
• Scalability: We had to scale the entire app just to handle high traffic on the “Search” feature.
• Knowledge: No single person understood the whole codebase.

The Solution: The Strangler Fig Pattern

We didn’t do a “Big Bang” rewrite. Instead, we used the Strangler Fig Pattern—building new services around the edges and slowly redirecting traffic.

Phase 1: The API Gateway

We introduced an API Gateway (Kong) to route traffic. This allowed us to swap out endpoints without the frontend ever knowing.

Phase 2: Event-Driven Decomposition

Instead of synchronous REST calls, we used RabbitMQ for inter-service communication.

• Example: When an “Order” is placed, the Order Service emits an event. The Inventory and Email services consume that event independently.

The Results

Lesson Learned

Microservices are not free. They trade “Code Complexity” for “Operational Complexity.” Only move to microservices if your organizational scale demands it.