A microservice composition approach based on the choreography of BPMN fragments

Abstract Context Microservices must be composed to provide users with complex and elaborated functionalities. It seems that the decentralized nature of microservices makes a choreography style more appropriate to achieve such cooperation, where lighter solutions based on asynchronous events are generally used. However, a microservice composition based on choreography distributes the flow logic of the composition among microservices making further analysis and updating difficult, i.e. there is not a big picture of the composition that facilitates these tasks. Business Process Model and Notation (BPMN) is the OMG standard developed to represent Business Processes (BPs), being widely used to define the big picture of such compositions. However, BPMN is usually considered in orchestration-based solutions, and orchestration can be a drawback to achieve the decoupling pursued by a microservice architecture. Objective Defining a microservice composition approach that allows us to create a composition in a BPMN model, which facilitates further analysis for taking engineering decisions, and execute them through an event-based choreography to have a high degree of decoupling and independence among microservices. Method We followed a research methodology for information systems that consists of a 5-step process: awareness of the problem, suggestion, development, evaluation, and conclusion. Results We presented a microservice composition approach based on the choreography of BPMN fragments. On the one hand, we propose to describe the big picture of the composition with a BPMN model, providing a valuable mechanism to analyse it when engineering decisions need to be taken. On the other hand, this model is split into fragments in order to be executed through an event-based choreography form, providing the high degree of decoupling among microservices demanded in this type of architecture. This composition approach is supported by a microservice architecture defined to achieve that both descriptions of a composition (big picture and split one) coexist. A realization of this architecture in Java/Spring technology is also presented. Conclusions The evaluation that is done to our work allows us to conclude that the proposed approach for composing microservices is more efficient than solutions based on ad-hoc development.