SOLID principles should better be applied when designing business objects, as soon as maintainability and modularity are needed. They bring uncoupling, abstraction and clean design to Object Oriented Programming. Microservices could be seen as SOLID principles applied to the Service Oriented Architecture. In respect to a classical monolith server, thanks to uncoupling and better granularity, you may enhance deployment, ease cooperation between dev teams, introduce Domain Driven Design and/or Event Driven Design, scale horizontally and still incorporate existing code and services.
After a quick and practical review of SOLID principles, we will see how they may apply to SOA, and how Microservices could be defined using the Open Source mORMot framework interface-based services, on Windows or Linux.