What is DDD and how was it used in the migration from monolith to microservices?

DDD (Domain-Driven Design) is an approach to software development focused on a deep understanding of the subject area and modeling its entities in code. When migrating from a monolith to microservices, DDD helps define the boundaries of contexts (Bounded Contexts), which become natural services.

Applying DDD during migration includes:

• Analyzing the subject area and identifying key aggregates and entities.
• Defining Bounded Contexts — areas within which models and terminology are unambiguous.
• Splitting the monolith into services based on these contexts to minimize coupling.
• Using Ubiquitous Language — a common language between developers and business for each area.

This enables creating microservices that reflect business logic and can be easily developed independently.