Microservices solve real problems: independent deployability, team autonomy, technology flexibility. They also create real problems: distributed transactions, network latency, operational complexity. Many teams split into microservices too early, before they understand their domain well enough to draw stable boundaries. Spring Modulith gives you module boundaries, enforced isolation, and event-driven decoupling inside a single deployable JAR. It’s the pragmatic middle ground. The Modular Monolith Problem It Solves A typical Spring Boot monolith looks like this after a year: