Converting a monolithic Spring Boot application into microservices involves identifying independent business capabilities, extracting each into its own deployable service, and establishing how those services will communicate.
Key Points: • Identify boundaries first by analyzing the monolith's modules and grouping functionality around business capabilities, using something like Domain-Driven Design's bounded contexts as a guide. • Create a separate Spring Boot project for each identified service, each with its own build, deployment pipeline, and database. • Define communication between services, typically REST APIs for synchronous needs and a messaging system like Kafka for asynchronous events. • A major challenge is managing the added operational complexity of running and coordinating many services instead of one deployable unit. • Data consistency becomes harder since each service now owns its own database, requiring patterns like sagas instead of simple local transactions. • Increased network latency and more complex troubleshooting are also common challenges, since a single business operation may now span several services connected over a network.
Example: Extracting the "Order Management" module of a monolithic e-commerce app into its own Spring Boot microservice with its own PostgreSQL database, and having it publish an "OrderCreated" Kafka event that the existing monolith (until fully migrated) and new Shipping Service both consume.
Interview Tip: A concise interview answer is:
"I'd start by identifying business-capability boundaries in the monolith, extract one at a time into its own Spring Boot service with its own database, and define REST or Kafka-based communication between them. The real challenges are less about the code and more about the new operational complexity — data consistency across services, added network latency, and harder cross-service debugging."