This document discusses Wix's transition from a monolithic eCommerce system to a microservices architecture using event sourcing and CQRS patterns. The old system had scaling issues as a single monolith. The new system decomposes functionality into independent microservices that are easier to develop and scale. It addresses problems like single points of failure, deployment challenges, and improving developer velocity with event sourcing and CQRS. Lessons learned include the complexity of these patterns, importance of frameworks, and handling data growth. The transition solved scalability and development speed at the cost of additional architectural complexity.