Use PHP to develop enterprise service systems. Different versions of the system must be provided for different customers. The system requirements of each version are mostly the same. How to avoid repeated development and maintain multiple versions, and how to design the front-end and back-end PHP. Can it improve scalability? The current idea is probably to split functions, modularize the front-end and add routing, dynamically generate pages, and split the backend into subsystems, modularize, and have finer granularity. However, there is no specific plan. Where can I find a reference?