Abstract

Microservice-based systems instantiate an architectural style that conceives of systems as sets of modular, customer-centric, independent, and scalable services. These systems express a similar essential structural organization and seems appropriate to design them using architectural patterns because these combine an understanding of the system domain and good practices. Code repository platforms provide the developer community with ideas and examples about microservice systems, but since they are in early adoption, there is still no clear notion of which actual microservice systems incarnate architectural patterns (if any), reducing the use of frameworks and the achievement of quality attributes. This paper extends a previous study on architectural patterns for microservices in academic and industry sources. We explored which architectural patterns for microservices are used in actual microservice-based open source systems, by subjecting thirty well-known open source projects to a comprehensive multicriteria code and design review. We found that (1) open source projects use only a few architectural patterns broadly; (2) most projects use the same few frameworks; (3) there are very few microservice architectural patterns as such; and (4) what most projects use (what was previously called) are SOA patterns. This study shows that microservice systems builders do use architectural patterns, but only a few of them. It remains to be determined whether additional patterns would be productively used to build microservice systems, or the few ones currently used are the only ones actually necessary.